 Hello everyone, welcome to Shankara AS Academy. Today we are going to discuss previous year science and technology question papers. Science and technology we will have two videos. Part one we are going to discuss three topics that is space science, astrophysics followed by that defense and green energy technologies. In part two we will be discussing biotech and other associated topics. So today we will start with question number one. From 2011 preliminary examination, satellites used for telecommunication delay or kept in geostationary orbit. A satellite is said to be in such orbit when and they have given four characteristics of the orbit. First one the satellite is geosynchronous. First we have to understand what is geosynchronous and then what is geostationary. To understand this we have to talk about the classification of the satellites. The satellite orbits or the satellites they can be divided into two types based on two factors. In fact first one is based on altitude, second one is based on orientation. So altitude means if you take the surface of earth how far the satellite is going to be located or at which altitude it is going to be located that is the first classification. And the second classification is based on orientation which means in which direction it is going to orbit. For example a satellite can orbit from pole to pole or a satellite can orbit in a slanting manner or a satellite can orbit right above the equator. So first classification is based on altitude, second classification is based on orientation. First starting with classification based on altitude. So lower orbit means a satellite which is placed up to 2000 kilometer from the surface of earth it is called as lower orbit. And a satellite which is placed from 2000 kilometer up to 35000 kilometer it is called as a medium earth orbit. And if a satellite is placed above 35000 kilometer and giving the approximate value then it is called as high earth orbit. Now coming to the next one polar orbit satellite means like I told you if this is the earth and if this is equator we are not considering the tilt of earth here. And if a satellite is going to orbit from north to south or from south to north that is from pole to pole then you call it as a polar orbit satellite. Now coming to the next one geosynchronous and geostationary earth orbit what is the difference between GSO that is geosynchronous orbit and GEO that is geostationary earth orbit. To understand this first you can write a general characteristic if time period of the satellite equals to rotational period of the earth which again equals to approximately 24 hours. When you read in geography you would have read 23 hours 56 minutes and 4 seconds so approximately we are keeping it as 24 hours. So if a time period of the satellite denoted by T equals to rotational period of the earth which again equals to 24 hours then you call it as geosynchronous orbit that is the earth is rotating and the satellite is also rotating in a synchronized manner so you call it as a geosynchronous orbit. Now geostationary earth orbit this is also a type of geosynchronous orbit but a special case so what is that special case see here geosynchronous orbit that is GSO it will not be placed above the equator generally but if you are going to place a geosynchronous orbit above the equator then you call it as geostationary earth orbit so I will repeat once again geosynchronous orbit means time period of the satellite equals to rotational period of the earth wherein geostationary earth orbit means it fulfills the same condition that is time period of the satellite equals to rotational period of the earth but at the same time it is going to be placed above the equator so this has a inclination that is GSO as inclination with respect to equator then if you take geostationary earth orbit inclination is 0 degree with respect to equator I hope you understand this Geo is a special case of GSO now based on this take a look at the statements given here first one the orbit is geosynchronous yes geostationary earth orbit is a type of geosynchronous orbit first one is correct the orbit is circular this is also correct the orbit is circular the orbit lies in the plane of earth's equator this is true geostationary earth orbit is a special case of geosynchronous orbit repeat geostationary earth orbit it's a special case of geosynchronous orbit and it is placed right above the equator which means the third one is also correct fourth one they have given orbit the orbit is at an altitude of 22,000 km no ideal should be 22,000 miles or 35,000 km so the third statement is wrong first, second and third statements are correct answer is 1, 2 and 3 coming to the next question. So this is a polar orbit satellite it is orbiting from pole to pole you call it as a polar orbit satellite but if it is going to orbit at a rate equal to the rotation of earth you call this geosynchronous and if it is going to be placed above the equator you call this geostationary earth orbit I hope you are clear about the satellite orbits coming to the next question. An artificial satellite orbiting around the earth does not fall down this is due to okay so to understand this keep in mind two important forces one is called as the centripetal force the other one is called as centrifugal force so centripetal force means the force that act that acts towards the center when something is falling down or when an object is in rotatory motion the force that acts towards the center it's called a centripetal force and the force that acts away from the center it's called as centrifugal force wherein here if you take this black dot to be satellite and this is earth now the gravity of the earth it tries to attract the satellite that is it provides acceleration due to gravity for the satellite to fall down but at the same time the satellite is propelling itself in a horizontal direction you can see two things here denoting V and A so A is the acceleration provided by the earth wherein V is the velocity of the or velocity provided by the satellite or the horizontal velocity provided by the satellite V's velocity is acceleration due to gravity now based on this the answer here should be it provides necessary acceleration for the motion that is attraction of the earth it is providing necessary acceleration for the motion so answer is D coming to the next question a question from 2011 UPSC preliminary examination they're asking the difference between asteroids and comets so first let's talk about asteroids asteroids they're generally called as minor planets wherein comets they're generally called as tail stars now second one if you take an asteroid generally it will be it will be made of rocks metals and other minerals wherein if you take comets they'll be made of or they will contain rocks metals minerals they will contain ice that is water and they will also contain hydrocarbons next talking about their origin if you take asteroid asteroids will be generally present between Mars and Jupiter but also keep in mind this is not the only place where the asteroids are present asteroids are present throughout the solar system we have near earth asteroids we have frozen asteroids there are different classification of the asteroids so generally the most of the asteroids are present between Mars and Jupiter coming to the comets they originate at a place called the Oot cloud which is outside the Kuiper belt and from here they orbit the Sun wherein the main similarity between these two both of them orbit around the Sun but if you take asteroids they almost have a elliptical orbit so it is mildly eccentric orbit repeat it has a mildly eccentric orbit then if you take a comet it has highly eccentric orbit these are the key differences now the main reason they get tail is the comets the main reason they get their tail is and they approach very closer to the Sun like this and they reach very closer to the Sun then the temperature increases since the temperature increases what happens the hydrocarbon starts burning or the ice starts melting and because of that it forms a dust type that's why we call them as the tail stars this is a key difference this is the path taken by a comet wherein generally asteroids will be taking a path like this mildly elliptical path wherein like I told you comets are present in Kuiper belt wherein asteroids they are present mainly between Mars and Jupiter but they're also present throughout the solar system in form of Trojan asteroids and other asteroids so based on this first one asteroids are small rocky planetoids while comets are formed of frozen gases held together by rock and metallic minerals this is definitely correct we saw the difference between these two first one is correct second one asteroids are found mostly between Jupiter and Mars while comets are found between Venus and Mercury this is wrong so first half of the statement is correct but the second half of the statement is wrongly given which means ultimately the second statement is wrong coming to the third statement comets show a perceptible glowing tail while asteroids do not show this is correct so which means answer should be one and three only answer for this one is one and three coming to the next question from UPSC preliminary examination 2012 they're asking which of the following is cited by the scientist as evidence or evidences for continued expansion of universe basically there are three different theories that talks about the origin of universe first one is the expanding universe theory you'd have heard about the big bang theory that talks about continued expansion where everything started from a very tiny point and the universe keeps on expanding the second one is called as the pulsating universe theory which says the universe keeps on expanding and at some point it'll again contract the other one is called as the static universe theory which says the universe is neither expanding nor contracting wherein the most widely accepted one is the expanding universe theory mainly because of its theoretical as well as practical evidences now here they're asking which of the following are evidence or evidences for continued expansion of the universe first one detection of microwave in space this is true I will explain about it second one observation of redshift phenomenon this is correct movement of asteroids is because of gravity not because of expansion of the universe third one is wrong occurrence of supernova explosions this happens when the stars massive stars reach the end of their life cycle so answer here should be one and two only now first of all what is cosmic microwave background or detection of microwaves in the space so there is a concept that you have to learn it's called as cosmic microwave background radiation CMBL so what happened is when everything started from a tiny point what we call as the big bang that happened approximately 13.8 billion years before the present date the universe was extremely hot repeat the universe was extremely hot and then slowly over time the universe started expanding and also it started cooling down so the initial radiation that formed before 400,000 years before the present date it is still emanating the space or it is still permeating the entire universe that radiation is called as cosmic microwave background basically if you are going to set up a microwave antenna and if you are not going to tune it to a particular satellite or anything still the antenna will heat that's because it will receive this radiation called as cosmic microwave background radiation basically microwaves are present in space wherein they do not come from astronomical object but they basically are emitted by the space itself that's because they were the initial radiation that formed in the universe these are called as cosmic microwave background which means this is definitely correct now coming to the redshift phenomenon so I told you the universe is constantly expanding starting from here the universe is constantly expanding which means let's say there is object A and then there is object B let's say this is a star if the light is emitted from the star before it reaches B what happens is the universe is expanding which means the space between A and B it just keeps on stretching you have to imagine space like a fabric even though you would have been imagining you know space like a empty thing understand space behaves like a fabric we call it as a space fabric so this fabric keeps on stretching or in other words it keeps on expanding when the fabric is expanding what happens the radiation emitted by this this also gets stretched out on other words the wavelength increases now if you take the visible light that is the part of the electromagnetic spectrum that is visible towards to the human eyes you generally call it as the whip jar so while it has shorter wavelength but red has longer wavelength so I'm writing lambda wavelength is higher for it lambda why wavelength is lesser for while it what happens here is when light is emitted from B towards A the space keeps on stretching which means since the space is stretching out the radiation appears to be shifting towards a red end of the spectrum so basically when there are two objects in space and if they are moving away from each other the light emitted by them it shifts towards red end of the spectrum now imagine the other way let's say two objects are approaching closer to each other so in this case light emitted by the object will appear to be shifting towards blue end of the spectrum that's called as blue shift so red shift means something is moving away from you blue shift means something is moving towards the observer this phenomenon is observed in all the galaxies that is if you observe a star not necessarily sun because we are in a single solar system when if you observe any galaxies or stars so if it is showing a red shift it means the object is moving away from us the astronomical object is moving away from us wherein if it is exhibiting blue shift it means the object is moving towards us based on this this is correct detection of microwaves this is correct observation of red shift both are evidences for expansion of the universe so the answer for this one is one and two only coming to the next question here the electrically charged particles from the space which are basically cosmic radiation whenever a star is exploring the cosmic rays will be emitted not to be confused with cosmic microwave background that is different that is just a microwave radiation here charged particles or highly ionizing particles which are emitted by the explosion of stars and other means they will be traveling towards the earth and here they are asking what prevents them from reaching the surface of earth so it is because of the earth's magnetic field there are two reasons or there are two main factors that are protecting us from all these ionizing radiation and also from these particles the first one is the earth's magnetic field I will summarize it here first factor is magnetic field of yet because when the particles are reaching here the magnetic field generated by the earth it will divert the particle which means the first line of defense for us is magnetic field of the earth second important thing is atmosphere of the earth these are the two factors that are protecting us from ionizing radiations here even though they have given a statement related to atmosphere but they have specifically given moisture in the upper layer of the atmosphere moisture basically means water vapor even though it plays a minor role the earth's magnetic field has a even more greater role and because of this the most relevant option here would be A that is the earth's magnetic field is diverting them towards its poles most towards the poles and then it is diverted and in fact this is the main reason we have evens like auroroborealysis or aurorostralysis because the particles are excited by the ionizing particles that is the particles in the atmosphere are excited by the ionizing particles go through it in your geography lesson now coming to the next question again from 2012 a person stood in the desert on a lone on a dark sky and he wants to reach a location which is located 5 kilometer to the east from the point okay so now he wants to in which location he should travel and he has to determine this based on pole star so the term pole star means wherever you stand in the earth the pole star will always be towards the north we call it as the pole artist star or pole star it will be always towards the north so imagine if you are standing somewhere and then if you are looking up and let's say the pole star is located in a particular direction so you have to align yourself towards the pole star and that will be the north direction if you are aligning our head straight towards the pole star that is the north direction now once the person turns towards the pole star he will be facing the north now he has to travel to the east which means he has to turn which means his left hand should be towards the pole star and based on that he has to walk so that he will just turn like this that is if he is turning like this his left hand will be towards the pole star and he has to walk straight in that direction based on this answer he should be direction keeping the pole star to his left repeat he should keep pole star to his left so that he will be walking towards the east end direction because his village is located five kilometer to the east answer is c coming to the next question question from 2015 in the context of modern scientific research consider the following statements about ice cube so ice cube it's basically observatory first one it's the world's largest neutrino detector encompassing a cubic kilometer of ice this is true basically the observatory is present in in the deep ice region it's very deep inside ice first one is correct basically second one it is a powerful telescope to search for dark matter this is true so dark matter approximately 70 percent of the universe is made up of dark matter but we practically don't know what it is made of so we are trying to detect dark matter and then coming to the third one it is buried deep in the ice all the three statements are correct factual question all the three statements are correct related to the ice cube experiment answer is D coming to the next question related to goldilocks zone the term goldilocks zone is often seen in the news in the context of this is a very familiar question for science and they will pick one very important term and they will ask what is the context or what is the why it is seen in use similar to this single line question but if you don't know the concept you won't be able to answer now coming to the goldilocks zone concept imagine something like this if you take this as sun mercury is here and then venus earth Mars and then Jupiter I'm roughly drawing it here imagine the first scenario where earth and mercury are swapping their position that is mercury becomes the third plant in the solar system and earth becomes first plant in the solar system closer to sun what will happen the temperature will be extremely high which means the water will evaporate probably maybe the atmosphere will also escape which means it becomes a unhabitable planet so or in other words earth cannot be habitated if it is moving towards the sun like this imagine the next scenario where earth and Jupiter they're swapping their position what will happen in this case the temperature will drop that's because earth and Jupiter are swapping earth is moving away from the sun which means the water will become frozen and again the living condition will not exist on the earth so the region where the possibility of finding a habitable planet is more for example if you take venus earth and mars in case of the solar system they're not very close to the sun and also they're not very far away from the sun so that's called as a goldilocks zone the place where the possibility of finding habitable planet is more or in other words liquid water can exist such zone is called as goldilocks zone in fact goldilocks zone is not only for sun you take any star and if you move to a particular distance there will be a goldilocks zone but finding a planet is a different thing but goldilocks zone is there for every star it's not exclusive only to the sun based on this the limit of habitable zone it's for the search of earth like planets in the outer space that's because whenever we find a star the first thing we do is find its goldilocks zone and then search for a planet in that particular place because mostly those planets will have habitable conditions neither too hot nor too cold so this term is seen in the news because for the search of earth like planets in the outer space answer is c coming to the next question related to indian remote sensing satellites they're asking what what are the following which of the following activities can be carried out by indian remote sensing satellites generally the satellites of india can be divided into two if you visit the isros website they would have given two classification one is earth observation satellites any satellites that's used for recording a data or any satellite that's used for capturing a photograph using visible spectrum microwave or any spectrum you call it as earth observation satellite and the other one is communication satellites for understanding purpose i will give you a few examples earth observation satellite it includes all the mapping satellites or all the satellites used for espionage or spy purposes all these are or any satellite that's used for general civilian remote sensing they fall under earth observation satellites where in communication satellite it includes tv and radio broadcast or the telecommunication satellites or the weather monitoring satellites all these falls under the communication satellites wherein based on this take a look at this one assessment of crop productivity yes possible using remote sensing satellites that is the earth observation satellites locating groundwater resources yes it is possible mineral exploration yes it is possible we have satellites such as resource sad that are capable of doing it third one is correct telecommunication this should be eliminated because telecommunication falls under communication satellites so the answer here should be one two and three in fact the official answer key was one two and three but with a small change because for the 2015 timeline the answer is one two and three but for the present trend that is 2023 you can write answer should be one two three and five also performing traffic studies this is also possible using remote sensing satellites because we have very precise satellites such as Cartosat one of the it's called as India's eye in the sky provides the clearest image for civilian remote sensing so even though the official answer key given by UPSC for the 2015 year is one three and five understand if such question is asked in the present day the answer should be one two three and five coming to the next question these are the earth observation satellites of India before going for the examination try to learn about these three satellites Cartosat, Heises and Risat Cartosat is optical imaging satellite or it uses visible spectrum and then Heises it uses infrared plus visible spectrum Risat stands for radar imaging satellites it uses microwave for producing images these three are very important satellites please go through them coming to the next question the term in dark seen in the news it's in the context of dash so with respect to this the answer here should be India's underwater observatory to scientifically study the Arctic region ARC stands for Arctic region where in scientific establishment in Antarctic region it can be eliminated because in dark it stands for Arctic research so in fact this particular observatory it is placed between Norway and North Pole in dark is located here between Norway and North Pole when it is to study about the Arctic's climate and also to study about its influence on the monsoon so answer here is D coming to the next question 2016 preliminary question they have asked about Astrosat while we are familiarly or we are very interestingly following about Hubble Space Telescope or the James Webb Space Telescope please keep in mind India also has a space-based astronomical observatory in fact India's only space-based observatory it is called as Astrosat launched in the 2015 and it was asked in question 2016 it is active till now I repeat Astrosat is active till now based on this two statements are given first one other than USA and Russia India is the only country to have launched a similar observatory in space this is a wrong because many other countries Europe Japan they have space observatories which means the first statement is wrong Astrosat is a 2000 kilograms satellite placed in orbit 1,650 kilometer above the surface this is a wrong even though it may look like a very memory-based question there is a small analytical aspect to this because Astrosat for people who were writing the exam in 2016 they were very familiar with Astrosat. Astrosat was launched using PSLV that is the Polar Satellite Launch Vehicle and if you see the launch capacity of Polar Satellite Launch Vehicle to the lower th orbit that is up to 2000 kilometer like we discussed in the very first question to the lower th orbit it can carry up to 750 kilogram and then to the geostationary transfer orbit it can carry up to 1425 kilogram which means it is impossible that India would have launched a 2000 kilogram satellite using a PSLV which means Astrosat should be less than 2000 kilogram based on this you can eliminate this option answer for this question is neither one nor two both the statements are wrong the next question is about Mangalyan mission 2016 UPSC question the first statement they have given the Mangalyan launched by ISRO is also called as Mars Orbiter Mission this is true Mangalyan is also called as MOM that is Mars Orbiter Mission first statement is correct second made India the second country to have a spacecraft orbit the Mars after USA no here they are not talking about landing here we are discussing about general Martian mission which means many countries have sent orbiter missions second one is wrong made India the only country to be successful in making its spacecraft orbit the Mars in its first attempt or maiden attempt this is also correct answer is one and three answer is one and three first statement is correct because it's called as Mars Orbiter Mission second statement is wrong because many countries have sent orbiters third statement is correct because India was the only country I repeat India was the only country to be successful in a Martian mission in its maiden attempt so for 2016 timeline the official answer key was one and three now if this question is asked in 2023 the answer should have been one only why that's because recently a mission called al-amal was sent al-amal or otherwise called as the Hope Mars Mission al-amal or Hope Mars Mission so this is a Martian Orbiter which is operating right now first one name of the mission second one it's a Martian Orbiter third important thing it was built by United Arab Emirates the first Arab nation to design a Martian mission fourth important thing this was launched by Japanese Aerospace Exploration Agency this was sent in there 2020 and it was successful also basically three important missions were sent in 2020 to Mars first one is the Mars 2020 by NASA second one was Tianwen which was sent by Chinese National Space Administration third one was al-amal mission which was sent by United Arab Emirates and all the three were successful in there 2020 even though it was launched in 2020 but it reached a bit later so this statement is wrong for the present timeline that's because the statement should have been made India the first country to be successful in the maiden attempt because right now this record is shared between India and United Arab Emirates so which means as per the official answer key answer is one and three but based on the updated data the answer should be one only is it clear can you go to the next one coming to the 2017 question the terms event horizon singularity string theory standard model all these are seen in news related to observation and understanding of the universe so first we'll talk about event horizon and singularity if you take a black hole the centermost part of the black hole is called as singularity so what exactly is singularity we don't know it is considered to be a point mass which means it's a it's a it's a point where the entire mass is compressed it's not three-dimensional there is no volume but still it has a lot of materials inside so singularity is a single point where everything is compressed and then the outermost border of the black hole on other words the outermost field of influence exhibited by the black hole that is called as event horizon now why event horizon is important because if any object is traveling closer to the event horizon I repeat closer not inside the event horizon but closer to the event horizon because of the warping of the space time it will bend let's let's take a light is traveling closer to the event horizon it's going to bend but if a light or any radiation is going to enter into the event horizon understand this will be trapped inside this just gets compressed and stored inside the singularity so near the event horizon it will bend inside the event horizon it will be trapped so both event horizon and singularity these are the terms related to black holes okay now coming to so the string theory the theory basically says particles are not like objects but rather it's like a one-dimensional string that's going to vibrate frequencies which means all the objects they're not to be considered as a particle they are particles but they're not like objects but rather they just emit different frequencies the theory is called a string theory wherein the vibration it depends on masses and also depends on property of the matter this theory is called a sting theory a very complex theory but we'll learn about it later and then so which means sting theory is related to particles particles emitting a particular frequency now coming to the standard model so under standard model we have different particles elementary particles which are divided into fermions and bosons basically quarks are the materials that make up headrons such as protons and neutrons where an electrons belong to leptons wherein standard model it's a it's a theoretical framework that talks about behavior of the subatomic particles so again coming to this point standard model it talks about behavior of subatomic particles even though you might not be very clear about the theories here still you can answer this question because even horizon and singularity is related to black hole sting theory is related to particles and the frequency emitted by them standard model is related to behavior of subatomic particles so the most optimum answer here should be observation and understanding of the universe answer is a coming to the next question the famous question related to elisa evolve the laser interferometer space antenna so what is the purpose of elisa experiment it is to detect gravitational waves what do we know about the gravitational waves first important thing is gravitational waves they are ripples created in the space due to high energy events for example collision of black holes collision of neutron stars or a single neutron star that may be spinning at a high velocity all these will create gravitational waves now these gravitational waves they travel at the velocity of light repeat they are more like a shock wave but they travel at velocity of light now the most important property of the gravitational waves is they will subject the objects to stretching and squeezing which means the objects will get elongated horizontally and compressed vertically and then next instant it will be elongated vertically and then compressed horizontally so it is a very lengthy concept you can search and learn this wherein the gravitational wave will subject the space and also objects to a moderate amount a very tiny amount of stretching and squeezing so based on this we designed or I mean the man can design observatory called as elisa evolve the laser interferometer space antenna which means it contains three spacecrafts the first spacecraft second and third and all of them they are separated at least by one million kilometer they are present in the space they form a triangle and they are separated by one million kilometer each and they will be shining laser light between them now what happens here is whenever gravitational waves are passing through the elisa experiment it will subject all of them through a small amount of stretching which means the distance between the spacecraft one two and three will be mildly altered and this alterations are recorded and it is taken as a detection of gravitational wave just like how we have the LIGO experiment where one is also constructed in India so LIGO or KAGRA or you say GEO 600 or Virgo all these are designed for gravitational wave observation but understand all these are present on the ground these are ground based observatories wherein elisa is a similar observatory but it is placed in space so answer here is to detect gravitational waves answer is B coming to the next question interestingly this was a question asked in 2017 they asked the purpose of the experiment and in 2020 they asked the same question but in a different manner so remember this elisa three spacecrafts they're flying in a triangular form and then if a gravitational wave is passing the distance between them will change now read this statement 2020 UPS equation the experiment will employ trio of spacecraft flying in formation of a equilateral triangle separated by 1 million kilometer laser is shining between them so which means it is elisa experiment evolved a laser interferometer space antenna experiment answer here is D it's a it's a concept that was repeated this is the main reason we tell you to revise old question papers because 2017 from elisa experiment again from 2020 a question was asked from elisa experiment please go through old question papers coming to the 2019 UPS equation related to IRNSS that is indian regional navigation satellite system so based on IRNSS which is right now renamed as navigation of indian constellation three statements are given IRNSS has three satellites in geostationary earth orbit and four satellites in geosynchronous orbit do you remember geostationary earth orbit and geosynchronous the one that is filtered from equator it's called as GSO and the one that is placed above the equator it's called as GEO the first statement is correct till date even right now we have three satellites that are located in geostationary earth orbit and then we have four satellites that are located in geosynchronous orbit so the first statement is definitely correct coming to the second one IRNSS that is a navik system it covers entire india and about 5500 square kilometer beyond its border this is wrong basically it covers entire india there is no doubt in this but it covers somewhere around at least around 1500 square kilometer from the border 5500 kilometer is not officially confirmed which means first one is correct second one is wrong third one india will have its own satellite navigation system with full global coverage by middle of 2019 this is wrong because india set targets to somewhere around 2030 which is further extended so answer here is one and two only understand this is a regional navigation satellite system so basically navigation systems they can be broadly divided into two one is global navigational satellite system the other one is regional navigation satellite system so GNSS global navigation system means they coverages worldwide that is starting from Arctic to Antarctic you can use the navigation system so we have four global navigation systems right now one is the GPS owned by USA the other one is GLONASS owned by Russia the other one is GALAILIO owned by the European Union owned and operated by European Union the fourth one is Baidu that is owned and operated by China okay four global navigation systems and there are many regional navigation systems I'm listing two of them first one is IRNSS that is Indian Regional Navigation Satellite System or otherwise called as NAVIC second one is quasi-zeneith satellite system that is owned by Japan these are regional in nature so first one is correct second one is wrong third one is wrong because we don't have a full global coverage when if you see here the dotted circle here I repeat the dotted circle shown in shown on the map here these are considered to be primary service area where the accuracy will be high wherein the dotted square here these are considered to be secondary service area where the accuracy will be modded but still you will get coverage but once we cross this dotted square that is once you cross this region you will not receive the signals at all let's say you are present somewhere in France or Spain here IRNSS coverage will be totally absent or in other words the coverage will not be received the signal will not be received which means it's a regional navigation system answer for this question is one only coming to the next question related to light 2018 question first one light is affected by gravity this is definitely correct because understand there is a concept called warping of space time which means space is like a fabric and let's say there is a heavy object with a particular mass and gravity the space will basically bend something like this if you take earth earth is also heavy so earth is also basically bending the space second one the universe is constantly expanding this is true which was proven by Hubble's law but it was also predicted by Albert Einstein's general theory of relativity so they're asking which of the following are prediction or predictions made by general theory of relativity first one was predicted by Einstein that is light is affected by gravity it was predicted by Einstein second one universe is constantly expanding this was also predicted by Einstein matter warps its surrounding space time this is also true this was also predicted by Einstein's theory of relativity which means answer here should be one two and three so everything in the space it is warping the space time and when a light is traveling around it let it be a star or be it a galaxy they will be subjected to bending or warping answer is all the above coming to the next question which of the following is the reason why astronomical distances are measured in light here it's because speed of light is always same we can eliminate other things distance among the stellar bodies do not change this is wrong because this is against the expanding universe theory which means this statement can be eliminated gravity of the stellar bodies do not change no gravity of the stellar bodies can change let's say they're undergoing collision a larger object is formed and because of other fluctuations gravity will change light always travels in straight line no because we saw in the previous question light is affected by gravity wherein speed of light is always same which means keep in mind you have studied that velocity of light is 3 into 10 per 8 meter per second but this is applicable only for vacuum not in all the mediums if you take different medium so the velocity of light keeps on decreasing if the density increases the velocity velocity it decreases for the light so here you have to implicitly understand speed of light is always same in vacuum or space and that is why we use it for measuring astronomical distances answer is d even the official answer q was d answer here is speed of light is always same coming to the next question related to India's satellite launch vehicles first statement PSLV satellite launch vehicle is useful for earth resource monitoring whereas GSLVs are designed mainly to launch communication satellites generally speaking this is true that's because the maximum launch capacity of PSLV like I told you it's up to 1750 kilogram but if you take the GSLV mark 3 for example the heaviest launch vehicle of India this can carry up to 8000 kilogram to the lower th orbit repeat to the lower th orbit so lower th orbit is where you place generally the earth observation satellites but when it comes to communication satellites for example this can carry only up to 1425 kilogram to the GTO which means it's very lesser but GSLV mark 3 can carry somewhere up to 4000 kilogram to the geostationary transfer orbit so keep in mind lower th orbit generally for earth observation satellites GTO or higher th orbit generally for communication satellites so based on a very generalized understanding first statement is correct second statement satellites launched by PSLV appears to remain permanently fixed in same position so here they are giving the description of geostationary earth orbit geostationary earth orbit satellites are usually launched by GSLV so which means this is wrong if a satellite look appears to be fixed it means it's geosynchronous that is like I told you earlier time period of the satellite equals to rotational period of the earth which equals to 24 hours and also you're going to place it above the equator if two conditions are made they're called as GEO and PSLV generally does not take satellites up to GEO second statement is wrong third one GSLV is a four state GSLV mark 3 is a four stage here itself it is wrong because it's a three stage one with first and three stages using solid and liquid motors that is first and third are using solid second and fourth are using liquid the entire statement is wrongly framed so answer for this question is A1 only the first statement is wrong keep in mind India uses three types of fuels that is it uses solid fuel generally HDP be hydroxyl terminated polybutadiene and we also use India uses liquid propellant this is generally useful for exo-atmospheric that is once the satellite launch vehicle crosses atmosphere it requires oxygen supply so these liquid propellants use two combination fuel plus oxidizer fuel is for providing energy oxidizer is for providing oxygen supply the third one is we also use cryogenic fuel so here also there will be a fuel plus oxidizer combo wherein we use liquid hydrogenous fuel and liquid oxygen as oxidizer now the list of all solid liquid and cryogenic fuels are given here you can go through it but please don't memorize it is not required based on this GSLV mark 3 it uses cryogenic engine and liquid propellant which means it uses liquid hydrogen and oxygen along with one of these liquid propellants so the third statement is wrong it is not using a solid rocket motor and it uses liquid but not in second and fourth stages initially it will be using different stages so GSLV mark 3 like I told you it uses a mix of solid liquid and cryogenic repeat please change the statement which I told you earlier it uses solid only the boosters are solid boosters or the strap on motors it uses solid followed by that the second stage will be liquid that is the main stage will be liquid and then the cryogenic stage will be cryogenic propellant so it uses all the three it's only three stages but the first stage is solid there is a booster second stage is liquid third stage is cryogenic so answer here is one only coming to the next question 2019 recently scientists have witnessed the merger of giant black holes whenever black holes merge they will emit gravitational waves we have discussed it earlier any high energy event it will emit a gravitational wave collision of black holes collision of neutron stars or a fast spinning neutron stars all these it emits gravitational waves so especially when these waves or when these black holes merge together they emit something called as compact binary in spiral gravitational waves a particular type of transient gravitational wave called us compact binary in spiral so answer is b other things you can easily eliminate because Higgs bosons no when black holes merge they do not emit particles so it's not possible to detect Higgs boson possibility of intergalactic space travel you can very well see that it should be wrong we have not discovered anything like that it enables the scientist to understand singularity this is wrong because singularity it's like a dividing by zero error we don't know what exactly singularity singularity is purely theoretical we don't know what exactly singularity coming to the next question so when the black holes merge understand it emits cosmic chips or otherwise called as gravitational waves coming to the next one 2019 question recently there was a growing awareness in the country about importance of Himalayan nettle it's a type of textile fiber answer is d type of factual question it's a textile fiber which is grown in the Hindukush Himalayan region when the importance of this one is it has a very high demand in national and international market because of the texture of the cloth it is grown in Nepal and Hindukush Himalaya's region where in the bedspreads or any other not the garments but the cloths made of the Himalayan nettle they are of high demand both in international and the national market so answer for this one is textile fiber coming to the next question 2014 question we are going to talk about Agni4 missile Agni4 missile which of the following statements are correct first one the surface to surface missile definitely is Agni4 can be surface to surface also second one it's fueled by liquid propellant one you know it is propelled by two stage solid propellant third one it can deliver one ton nuclear warrant up to 7500 kilometers this is wrong wherein we have been testing different versions of Agni wherein Agni4 it has a claimed range of up to 4000 kilometers Agni5's intercontinental ballistic missile which means it can reach up to 7000-8000 kilometer even though the data is not publicly disclosed so first is correct second is wrong third is wrong answer should be one only answer for this one is one only coming to the next question related to INS Astradharini so INS Astradharini it's a torpedo launch and recovery vessel developed by India which means torpedo means these are underwater missiles which can generally target two things one is it can target submarines second it can target other ships it can destroy the ships based on this answer should be torpedo launch and recovery vessel answer for this question is C coming to the next question what is terminal high altitude area defense third sometimes seen in the news it's basically American anti missile system in recent times you have been learning about S 400 missile system which is imported or which is exported by Russia to India similar to that you would be learning about S 500 also which is being developed by Russia and similar to that you also would have heard about iron dome iron dome rocket defense system which is developed by Israel these are by Russia similar to that there's a system in USA called third system which means Israeli radar system they have given this to confuse this is iron dome rocket defense system basically these are interceptor systems which means if a ballistic missile or if the cruise missile is approaching a particular area so we can launch anti ballistic missiles or anti missiles that can destroy the oncoming missile system so third is a American anti missile system generally these setups will have a radar and then it will have a fire control system and then it will have a launcher system so if there is an incoming threat first that radar will lock the target and then the control system will tell to fire and then the launchers will launch the missile that's how it generally works you can go through the S 400 system also since it's very important for the upcoming examination the last year we had it in UPSC mains so this year you may get it in problems also please go through it coming to the next question the last year question related to fractional orbital bombardment system so in this case a missile put into a stable orbit that around the earth and deorbit over a target on the earth answer is C so what is the difference between a normal bombardment system and a fractional orbital bombardment system what happens here is let's say you are launching a missile from point A to point B and let's say there's a curvature of earth like this generally what happens is on B there will be a radar system so if the missile is traveling like this the probable direction if it is traveling they can detect it using the radar and they can even use a counter attack anti missile system when in case of fractional orbital bombardment it is first stabilized just similar to a satellite that is point A to point B but we are not using the target like this we are not approaching like this but instead what happens is first it is stabilized like a satellite and then it makes orbit around the earth outside the atmosphere it is exo atmospheric that is it travels outside the atmosphere and then when it is very closer to the target this will just deorbit and then it will hit the target what happens you are approaching a particular target from an unexpected location to make a surprise attack and most importantly the missile system initially will look like a satellite system because it is orbiting around the earth it looks like a satellite system it's more like a method of surprise attack answer is C a missile put in stable orbit around the earth and deorbit over a target on the earth coming to the next question so we have completed space science astrophysics and defense if you have been following properly and this one we are starting with green energy technology from this question it is green energy technology in union budget 2011 and 12 a full exemption for basic custom duty was extended for bio asphalt so they are asking what are the importance of the material unlike traditional asphalt bio asphalt is not based on fossil fuel this is true it's not based on fossil fuel it is generally manufactured from renewable sources such as sugar or any other crop materials or even agricultural residues bio asphalt can be made from non-renewable sources no if you are making from non-renewable sources that will not be accounted as bio asphalt and no exemption for customs duty is given second one is wrong bio asphalt can be made from organic waste material this is true any organic waste material like wasted food grains or spoiled food grains or even any biological material can be used for making bio asphalt it's a co-friendly to use bio asphalt for surfacing the roads this is true so answer should be one three and four answer is b answer is b so it is generally made from sugar molasses rice corn potato starches it is generally manufactured from renewable sources not from non-renewable sources answer is one three and four coming to the next question next we have question related to microbial fuel cell 2011 microbial fuel cells are considered as a source of sustainable energy definitely yes they're asking the reasons first one they use living organism as catalyst to generate electricity from certain substrates this is true because it generally uses geobacter or it uses the schwannler type of bacterias to produce electricity so first one is correct second one they use a variety of inorganic materials as substrates generally organic materials are used as substrate here see here they're capable of transferring electrons from organic matter to the electrode these bacterias they generally work only on organic matter not on synthetic or non-organic matter which means second statement is wrong coming to the third statement the third statement says they can be installed in wastewater treatment plants to cleanse the water and produce electricity this is true wherever the microbes can be accumulated they can cause electron transfer which means third statement is correct first statement is correct but the second statement is wrong answer is one and three only one and three only if you want you can pause the video and you can quickly go through this coming to the next question we have a question related to CFL and LED lamps 2011 question to produce a light a CFL uses mercury vapor and phosphor where LED uses semiconductor material this is true one important thing you have to understand about the CFL lamps is CFL generally emits ultraviolet I repeat CFL produces ultraviolet what happens is first of all ultraviolet radiation will be produced but human eyes are not sensitive to ultraviolet so we have to convert it into visible light what happens is if you have a CFL lamp or if you take a tube light first ultraviolet is emitted but this ultraviolet it is going to strike the phosphor coating that will excite them phosphor or mercury vapor coating that will excite them which will then emit visible light if you see here initially ultraviolet radiation is released and then ultraviolet radiation is exciting the phosphor or mercury vapor then it is converted into visible light so the first statement to produce light a CFL uses mercury vapor and phosphor true LED lamp uses semiconductor material true because it uses a PN junction diode a forward biased PN junction diode is used P type semiconductor and N type semiconductor joined together first one is true average lifespan of CFL is much longer than LED logically you can eliminate this because since LED is more efficient and also they have a longer lifespan that's the reason mainly we are installing it in street lights also generally LED lamps have longer running hours than CFL lamps second one is wrong CFL is less energy efficient as compared to LED true LED uses only a fraction of power compared to the CFL lamp considerably lesser answer is 1 and 3 only answer is 1 and 3 coming to the 2012 question related to biomass gasification so biomass gasification means it's a process that converts biomass you take wood or agricultural waste or any other thing it is converted into a gas it's called as the sin gas or sometimes synthetic gas or sometimes it called as the producer gas you are burning the biomass in limited supply of air and then you are converting it into energy intensive gas biomass is converted into gas the advantage is whenever we require heat in an industry instead of burning the biomass we can burn the sin gas it emits very lesser amount of carbon monoxide that is the main advantage of this first one coconut shells ground nutshells rises can be used in biomass gasification true the combustible gas generated from biomass gasification consists of hydrogen and carbon dioxide only the problem is with the term only because it contains hydrogen carbon monoxide some amount of methane carbon dioxide it's a mixture of different gases not just carbon dioxide and hydrogen so the second statement is wrong first statement is correct second statement is wrong third one the combustible gases generated from biomass gasification can be used for direct heat generation true but not an internal combustion engines wrong it can be used in internal combustion engines also just like how we use a liquefied natural gas or compressed natural gas you can use this also even though a mild alteration may be required in the system sin gas can be used in internal combustion engines including the generators also so third one is wrong second one is wrong first one is correct answer here is A11D for biomass gasification answer is A11D coming to the next question you can pause the video and if you want you can quickly read it or otherwise we have provided the PDF you can go through the PDF also coming to the next question it is related to ultraviolet radiation uv radiation in water purification systems they're asking what is the role of uv radiation in water purification systems first one it inactivates or kills the harmful microorganisms true what happens is ultraviolet has a very short wavelength wavelength is lesser energy is higher and frequency is also higher so this could break the DNA or RNA present in the microorganism which means they are not capable of replicating and generally it kills the microorganism first one is definitely true it removes all undesirable orders no ultraviolet radiation will only purify the water but it will not remove the undesirable orders second one is wrong we generally use uvc ultraviolet C which is a low wavelength and high energy radiation third one it quickens the sedimentation of solid particles no maybe potash alum or other chemicals can do this it removes the turbidity it improves the clarity of the water it gives us characteristic taste but the taste order all these will not be altered by uv uv will only kill the bacteria or any other microorganisms present in the water answer for this one is A11D coming to the next question with reference to usefulness of byproducts of the sugar industry okay which of the following statements are correct baggies can be used as a biomass fuel for generating energy this is true basically the leftover product from the sugar industry after extracting the sugar can juice the remaining product is called as molasses so the baggies can be used as a biomass fuel for generation of electricity this is true second one molasses can be used as one of the feedstock for the production of synthetic chemical fertilizers it's a wrong that's because synthetic chemical fertilizer it is generally uses NPK that is nitrogen, phosphorus and potassium but if you take the molasses molasses will be rich in calcium it will have magnesium and then it will have a lot of iron wherein here we require sodium potassium sorry nitrogen potassium and phosphorus synthetic fertilizers it requires nitrogen phosphorus and potassium wherein molasses contains or it is rich in calcium magnesium and iron so because of this it cannot be used for manufacturing synthetic fertilizers first one is correct second one is wrong coming to the third one molasses can be used for production of ethanol this is correct answer is 1 and 3 only 2013 question answer is 1 and 3 only molasses cannot be used for manufacturing synthetic fertilizers coming to the next question related to solar power production with reference to the technologies for solar power production consider the following statements first one photovoltaic is a technology that generates electricity by directly direct conversion of light into electricity this is true we have a solar photovoltaic cells that contains p-type and n-type semiconductors generally n-type is kept on the top repeat p-type and n-type semiconductors n-type semiconductors will have extra electrons p-type semiconductors will have holes now the general structure goes like this we will draw it with little more clarity here you have n-type and then you have p-type n-type contains a lot of electron additional electron p-type p-type contains vacancy for electron and between these two you have a metal connection now what happens is whenever solar radiation is striking the n-type semiconductor the electrons will be knocked out now these electrons for virus connected here the electrons will travel from here towards the p-type which generates electricity and then the electrons will return to the n-type through the metal that is metal connection that is kept here this is how the solar photovoltaics will work the PV cells solar photovoltaic cells first half of the statement is correct solar thermal is a technology that utilizes suns rays to generate heat directly from it that is also true that is because it employs things such as concave mirror if you take a concave mirror the light will be focused at the point so at the focal point the intensity will be high since intensity is high heat generated is also high here what happens sunlight falls on the concave mirror everything gets converged at a place that is used for heating a water that again can get converted into steam it spins a turbine so similar to nuclear energy or any other forms of energy solar thermal is a method by a method of generating electricity by spinning the turbines in this case you are using water the water has to be heated heat is provided by the sunlight do you understand so photovoltaic sunlight knocks out electron and that is used for producing electricity solar thermal energy sunlight is used for heating water the water generates steam the steam is used for spinning the turbine which is attached to a generator which again produces electricity which means first statement is correct solar photovoltaic generates alternating current no solar photovoltaic generates direct current only when you use a generator it produces alternating current so the second one is wrong India has manufacturing base for solar thermal technology but not for solar photovoltaic no India has manufacturing base both for solar thermal and solar photovoltaic even though we depend heavily on imports we cannot necessarily say that there is no base at all second and third are wrong first one is correct answer is a 2014 question answer is a coming to the next question related to maize maize can be used for production of stars true oil extracted from maize can be a feedstock for biodiesel true alcoholic beverages can be produced by using maize this is also all the three statements are correct answer is the all the above all the three statements are correct coming to the next question with reference to fuel cells familiarly seen in news recently we have a hydrogen based fuel cells and we have different types of fuel cells first one understand how it works what happens is on one side we will be feeding hydrogen on the other side of the cell we will be giving oxygen wherein there is a polymer electrolyte membrane when hydrogen oxygen combined with each other so the hydrogen will emit electrons so the electrons will travel here since the electrons are emitted or electrons travel in the external circuit it produces electricity so generally you remember it has one side and it has other side that is hydrogen is capable of ionizing getting ionized so hydrogen is giving of electrons and then oxygen it is receiving electrons so electrons moves in the external circuit which creates a current this is how the fuel cell works a very simplified definition or understanding for a fuel cell first one if pure hydrogen is used as fuel the fuel cell emits only heat and water this is true because hydrogen and oxygen combines here they will form only steam here no other byproducts first one is true fuel cell can be used for powering buildings and also for small devices fuel cells can be designed in any sizes second one is wrong fuel cells produce electricity in form of alternating current this is also wrong because I like I told you if it is a generator it will produce alternating current wherein if it is a battery or anything it produces direct current batteries produce or battery store direct current third one is wrong answer is one only 2015 question answer is one only coming to the 2016 question related to bureau of energy efficiency star label they're asking which of the in which of the following you can find the bureau of energy efficiency star label basically in all electronic equipments all the electronic or all the consumer electronics you can find it so answer for this one is D12 and 3 2016 question answer is D12 and 3 coming to the next one 2017 question related to OLED that is organic light emitting diodes so they are used to create digital displays and they're asking what are the advantages of OLED OLED display can be fabricated on flexible plastic substrates true the main advantages it has a cathode and anode and it uses a type of organic compound that emits light when the advantage here is all these are very thin and mostly transparent layers the conductive layer and also the emissive layer they're mostly transparent which means they can be flexible they can be rolled up and most importantly they are transparent also all these are advantages of organic light emitting diodes first one it says it's flexible second one it says it can be rolled up into displays the third one it says it is transparent all the three are correct in fact right now we have folding type of phones you have the galaxy z fold and all these or the pixel seven fold that's coming up all these are based on oi LEDs that's because the display is very flexible answer is D coming to the next question related to biofuels 2017 question related to biofuels it's possible to produce algae based biofuel that's because if you see the different generations of biofuel the first generation biofuel it used sugar beet sugar cane second generation it used wood straws glass grass waste and everything third generation is based on algae fourth generation will be based on much advanced gas gasification processes or it may even involve genetic engineering now when we talk about algae based biofuels first statement production of algae based biofuel is possible in sea only no it can be produced in any water body even in a pond or in a lake first one is wrong setting up and engineering the algae based biofuel production requires high level of expertise in technology until the construction is completed this is true economically be viable production necessitates the setting up of large scale facilities which may rise ecological and ecological and social concerns this is also correct because generally open algal ponds it'll insect a lot of you know larvae invasion and because of that it rises ecological concerns because mosquito population or other insect population may rise because you're putting more algae in a pond and other thing is when the algae is filled in a pond so other life cannot survive let's say fishes or other things cannot be grown in that because hypoxia the sunlight will not reach oxygen production is also lesser so only the surface can have alga so there are many ecological concerns in this answer is 2 and 3 2017 question answer is 2 and 3 coming to the next question 2018 question with reference to the solar power production in India consider the following statements India's the third largest in the world in a production of silicon wafers no India's lagging in silicon wafers in fact there are many articles related to it we heavily depend on import from China Taiwan and other countries first one is wrong solar power tariffs are determined by solar energy corporation of India this is also wrong answer is neither one nor two because solar power tariffs they are determined by the Central Electric Regulatory Commission CERC which is a statutory body Central Electric Regulatory Commission it is regulating the solar power tariffs in India so both the statements are wrong coming to the next question a question from 2019 in the context of which one of the following are the terms pyrolysis and plasma gasification related they are related to waste to energy technologies which means if you have agriculture waste or any waste it can be converted into energy so pyrolysis if you take it's a thermal process basically it involves heating such as any biomass can be broken into smaller molecules and it can be used to convert into gas liquid or solid fuels that's called as pyrolysis coming to plasma gasification it's a high temperature process wherein it uses plasma that is ionized gases are used and then if the waste is fed into the ionizing gases then it breaks down into smaller constituent atoms or molecules which again can be used as fuel so both plasma gasification and pyrolysis they are related to waste to energy technologies coming to the 2019 question again related to green energy technology in the context of proposals to the use of hydrogen enriched compressed natural gas the main advantage of hydrogen enriched compressed natural gases elimination of carbon monoxide emission no whenever you see such extreme words like elimination or it is absent these words you have to be very careful because it reduces by 70% compared to the normal CNG if you take the hydrogen enriched compressed natural gas the carbon monoxide emission reduces by 70% but it will not be eliminated even in hydrogen enriched car you know compressed natural gas carbon monoxide will be emitted no elimination first one is wrong second one hydrogen enriched compressed natural gas as fuel reduces carbon dioxide and car hydrocarbon emission this is true here they're talking about reduction not about elimination second one is true hydrogen up to one-fifth of the volume can be blended with CNG yes one-fifth of the volume of the CNG can be hydrogen third one is true hydrogen enriched CNG makes the fuel less expensive than CNG this is wrong it is for the environmental concern that we are enriching but generally the cost of the hydrogen enriched CNG by a small fraction is always higher than the normal CNG answer for this one should be two and three understand especially in areas where the pollution is high areas like Delhi they propose setting up hydrogen enriched vehicles that's because for mainly because of environmental concerns not because of lesser fuel cost so this is mainly for better environment not for better cost of the fuel coming to the next question the next question 2020 question is related to the usage of drones the following activities three activities are given which of the following can be successfully carried out by using drones all the three activities can be carried out using drones when most of the people had a confusion related to this collecting the breath samples of whales this is also possible there are cases where they collect the breath samples of the whale that will contain a small amount of saliva and other body fluids that can be used for the DNA analysis so there are many drones that collect you know the DNA from the whales by the liquid or the fluid answer is one two and three all the three are answers here coming to the last question for the present session according to national biofuel policy which of the following can be used as raw material for production of biofuel you have to keep one thing in mind when while answering this in fact there is a recent amendment for the national biofuel policy in 2023 whenever crop has to be used for biofuel food crops should not be diverted generally food crops will not be diverted but if grain is spoiled or if a food is spoiled or in other words if it is unfit for human consumption then it can be diverted for biofuel production so cassava damaged wheat grains can be used groundnut seed horse gram their food crops cannot be used rotten potatoes sugar beet first generation biofuel so one two four and five should be the answer one two sorry one two five one six should be the answer answer is a one two five one six because these two are food crops they cannot be diverted but if they have given something like this you know rotten groundnuts or horse grams unfit for human consumption then that can be used in production of biofuels but if it is in good state it cannot be used answer for this one should be one two five and six all right so we have completed three major topics that is space science and astrophysics followed by defense and then green energy technologies wherein I will see in the next session we will come up with more questions thank you very much for watching please do subscribe to the channel for more contents