 Induction quiz number one here we go a circular loop of wire has a diameter of point one meters if it's removed from a point five Tesla magnetic field in ten a point one seconds what's the average induced EMF so we're talking about a coil of wires in which case EMF is equal to negative N change in flux over change in time what's N I heard it you're right what yeah ah loop N is one be alert for that because they'll do that quite often because it makes the math easier but a lot of kids I can't see N anywhere well the word ah means one if they don't mention any other torments of wire so N is gonna be one what's the change in time point one seconds what's the change in flux that's what I'm gonna spend most of my math doing I'll do that over here change in anything is final minus initial and flux is magnetic field final times area minus magnetic field initial times area if I'm removed from the magnetic field what's my final magnetic field Jacob zero so as it turns out my change in flux is going to be zero minus my initial magnetic field which was point five times the area that was in the magnetic field I said they're gonna give you three shapes circle rectangle or square this time it's a circle and it's pi r squared now I have to be a bit careful they gave me the diameter so what's the radius point zero five and I'm running out of room mr. Dukes point zero five squared zero minus point five times pi times point zero five squared my change in flux is that there negative point zero zero three nine negative point zero zero three nine and now I'm gonna go walking back over here negative one negative point zero zero three nine but Erwin I'm gonna use my calculator value divided by point one the voltage that this would generate negative one times that answer divided by point one you get point zero three nine volts or am I wrong no one nodding yes zero point zero three nine volts not very much but rotating it at point one seconds is pretty small and that's a pretty small loop a point five meter long wire moves perpendicularly that's good that means it will have a voltage induce a voltage through magnetic field at a speed of 20 meters per second what's the induced EMF so the induced EMF BLV magnetic field is point four length of wire is point five the velocity is 20 point four times point five times 20 how many volts will we get four volts now be careful those of you that writing the provincial exam why would you lose a half mark stupidly here it's yeah one sig fig a lot of these may work out evenly don't forget two or three sig figs check your mock check your tests check your provincial those you're right eventually before you hand it in now I marked the physics 12 provincial once and on the physics 12 provincial on the actual marking day they decided that they would ignore sig figs but that was not in the rulebook that was just decided then so go over it those either right and provincial if the wire is part of a circuit with resistance six ohms what's the current okay current is voltage divided by resistance we have four volts divided by six ohms point six six seven amps two thirds of an amp number three okay here's back voltage armature of a DC motor has resistance of 1.6 ohms when it's stationary it's connected to a 12 volt battery at full speed the motor draws point six two amps of current what's the back emf well let's see the back emf is equal to the full voltage minus whatever is left inside the armature do I know my full voltage here 12 minus do I know the current when I'm running at full speed point six two do I know the resistance of my arm now I do often they won't tell you this often what they'll do is they'll tell you the current when it's stationary if you know the current when it's stationary what's the back voltage when it's stationary zero you'll know the source voltage and you can solve for the resistance this one here is just straight plug-and-chug though 11.9 am I wrong oh I did times thank you try that again 11 even 11 volts so there's still one volt in the actual arm of the motor that means there is still a net positive current in the arm of the motor some heat will still be generated but not much an ideal step-up transformer that means my secondary voltage is going to be bigger has 50 terms secondary coil has 100 sorry 1500 turns primary emf is 12 volts what's the secondary so voltage primary divided by n primary equals vs over good gosh mr. do it v yes this works what am I doing here try this again voltage primary over secondary equals n primary over n secondary the other way works as well but I was cross multiplying already I didn't need to we're gonna get a primary voltage of 120 secondary voltage is a mystery primary number of coils is 50 secondary number of coils is 1500 the secondary voltage is gonna be 120 times 1500 divided by 50 3600 volts is that right if the secondary current is 3 amps what's the primary current okay so I'm gonna use the number of coils because that's what they gave me the number of coils on the primary divided by the number of coils on the secondary equals the current on the secondary divided by the current in the primary and Evan you'll notice for current the S's and the P's don't line up current is the one that's opposite on your formula sheet but now it is straight straight plug-and-chug and cross multiply it's going to be 50 on the primary 1500 on the secondary equals current in the secondary is 3 primary current is don't know primary current is 3 times 1500 divided by 50 primary current is 900 or 90 90 there it is give yourself a score out of count them nine so some question and answers here number 16 from the induction review says the diagram below shows two coils in a magnetic field one where there is a flux one where there's a flux of zero an electric current can be induced in the coil oriented with its plane now a is wrong and the reason a is wrong is we said it's not the magnetic field that causes voltage the changing flux which is usually a changing magnetic field so a is wrong c is wrong okay either B or D now both of these have a changing magnetic field which of them then therefore also has a changing flux flux was what times what cross-sectional area what's the area here what's the flux here how many lines are going through this particular shape here so you know what you're not going to be able to generate a current right here so parallel note changing magnetic field here would do it in fact this would be exactly the same as when you move the magnet closer and closer to the coil that'd be an easy way to change the magnetic field move the magnet closer that means the magnetic fields getting stronger because you're getting closer D which I haven't circled but D is it okay next so I've had a request for kinematics for me or torque so let's try this first of all let's pause the recording for a second so I've been asked to do some kinematics review projectiles in particular so these are from old provincial exam questions you probably already have these somewhere in the kinematics review another teacher made these up but I'd already done mine but here's a good example a 15 kilogram rock is projected a projectile horizontally from a very high cliff with a speed of 65 meters per second we said Alyssa here was our strategy for projectiles we always broke everything into horizontal and vertical components and there was three well in particular two key ideas the fact that you knew the horizontal acceleration and you knew the vertical acceleration what's the horizontal acceleration of a projectile in our magic physics world where everything works nice zero what's the vertical acceleration in our magic physics world if we ignore air resistance negative 9.8 then almost always I said I'd like to know my horizontal velocity and my initial vertical velocity Aaron why didn't I put an initial right here well because the acceleration is zero there is no initial and final the horizontal is constant so in this diagram here why can I say that the split second I leave the cliff have I started falling yet so the split second I leave the cliff what's my initial vertical velocity zero my horizontal is that then often they'll give me a displacement in this question this time they didn't but if they gave me a displacement it would either give me the range horizontal I'd write it here or they'd give me the height negative because I've ended up below from where I started from I'd write it and then I'd ask what they want me to find almost always you're going to use this to find time and then use time to find whatever distance they want the only other question they're going to do is they're going to give you the time okay in which case that's usually easier now here they've given me what is the speed of the rock after it has fallen they've given me a vertical distance of so why is this wrong negative okay as soon as I have a vertical or horizontal displacement I bend my interest on that side to finding time of flight what equation do I have that has a v d and t in it ah the gold no d d equals vi t plus one half a t squared conveniently vi is zero so this whole term vanishes and in fact I really have here is d equals a t squared over let's get t by itself times by two divide by a square root that okay t is going to be times by two divide by a square root it's going to be the square root of two times negative thirty five divided by negative nine point eight my negatives cancel is a good thing two times negative thirty five divided by negative nine point eight square root time of flight is two point six seven three seconds now they could have asked me to now find the range the range would be this what happened to the half a t squared this zero on this side now they didn't ask me to find the range instead as an added twist what they're telling me to find is the oh you don't have the question in front of you speed okay I think the speed is this number right here this thing how can I find that oh it's a vector I think I can find it by going horizontal plus vertical the speed is right there it is oh what's the horizontal always sixty five what's the vertical is it zero no it wasn't the beginning now it has some downward velocity and in fact really I'm going to spend more time on this question finding a v y final v y final equals v y initial plus a t I think is what I'm going to use here I know is what I'm going to use here v y final is zero zip zilch nada explain it a is what negative nine point eight t is two point six seven three I'll get a negative answer which is good because it's going down negative nine point eight times two point six seven three so this number times negative nine point eight negative nine point eight mr. do it not times 98 you get twenty six point one nine six zero one seven one so negative negative twenty six point two so right here I can put a twenty six point two I can ditch the negative now because the arrow says it's pointing down how would I find v no that'd be to find an angle what I find v math eight I think it's girl v squared is going to be sixty five squared plus twenty six point two squared because I think in this question yeah they asked for speed not velocity velocity would then also require me to find an angle theta and then say that that angle was below the horizontal and it would be this angle right here but they didn't ask me to find that angle that should be the answer I hope I think I hope I think I hope Troy the clever boy he says mr. do it look I know horizontally is sixty five the vertical is going to get bigger and bigger and bigger which means my hypotenuse is going to get bigger and bigger and bigger and bigger what's the only hypotenuse bigger than sixty five in the question yeah Troy's irritating sometimes I should have spotted that actually well played you know what I'll even say that that's worth a candy so here's a classic written question stunt vehicle when our velocity was at an angle what did we do we never used it we're not going to use the 35 what did we do instead components and then it was going to be horizontal and vertical so the very first thing I would do and because I'm going to try and keep this all visible I'll do it over here so I would say here's 35 this angle I don't know if you guys can see is 28 degrees because it says I have v y initial and vx why didn't I put an initial on the vx because the horizontal never changes opposite hypotenuse adjacent I think v y initial ends up being sine fact it ends up being 35 I'm cutting corners here Melissa if that's okay 35 sine 28 and I think vx ends up being 35 cos 28 horizontal vertical and I've already answered a one of the vehicles oh well I haven't I haven't crunched the numbers yet mr. dook yeah thank you captain obvious make sure I'm in degrees I'm not done radians nice try 35 sine 28 16.43 I would go to two or three sig figs when I wrote my answer in a but I'm gonna spin extras because I know I'm gonna be using this 30.9 so vx 30.9 v y initial is 16.43 I also know both accelerations automatically if I'm in my magic physics world ignoring air resistance acceleration horizontally is what zero and vertically is now if I read this quiz question somewhere they gave me a distance they either gave me the range well I look actually know it looks like you're asking me to find the range so I doubt they gave it to me or they gave me a vertical distance the height of my job what is the vertical distance 52 so what's my vertical displacement negative 52 how many pieces of information do I have horizontally 2 how many I have vertically 3 here's where I can find time and here's what I'm gonna use d equals vi t plus a half at squared you're gonna get negative 52 equals vi 16.43 t minus 4.9 t squared where'd the negative 4.9 come from I did a half of 9.8 in my head because I've done it so often and I'm trying to save 30 seconds here wherever I came what kind of an equation is this why it's a quadratic how do I know go to squared how would I solve it make it equal to zero and then absolutely I would use the quadratic solver now having said that all of you listen up for a second you are totally allowed to use the quadratic solver but if you do use the quadratic solver just to fit to the marker you have to do this somewhere otherwise they may just assume that you cheated and copied the answer meanwhile I'm gonna use technology here's silver Paulie Smoltz press any key polynomial root finder degree 2 a negative 4.9 b 16.43 sorry those of you watching at home I don't have a I don't have a program installed on my virtual TI C 52 so I'm getting 5.34 and one more value that's negative that I will reject so I found B time of flight what does C want me to find C wanted me to find the vehicles range use DX equals BXT my horizontal was 30.9 time was 5.34 30.9 times 5.34 and I get 165 yards meters so there's a classic project watch but I would like to talk about what shows up on the written section so the first question on your written section of your mock exam and if you're writing the provincial same idea is either going to be kinematics and for kinematics it's almost always a projectile or airplane in a in a cross breeze so what's the ground velocity or often they'll give you the ground velocity and the and say subtract the vectors to find the airspeed or forces now for forces it's either going to be two masses or a ramp let me see if I can find you a good example of a question like that so the types of forces questions that you'll see on the written section so stuff like this make this a bit bigger so you can see a little easier okay here's a can going up a ramp with an initial velocity eventually it's going to come to a stop when will it come to a stop I think you'll need to find out the net acceleration by going winner minus loser components components components this is where we had parallel and perpendicular components or something like question number two where you have a ramp and the hanging mass an Atwood machine we called this so here you would have in fact let's do question number two together really quickly as an L quick review so it says find the acceleration and as a part B they can ask you to do something with the acceleration using DVT and VF and VI and all that stuff but here I would go like this I would say okay I have M2g and tension I would start there because that's the easiest mass and now I feel better and I called it M2 because we said we usually they will ask us from left to right what are the forces acting on this one here while I would have Mg down tension normal force at 90 degrees and friction however airy we said this this is good perpendicular these two are good because they're parallel to the rope gravity is the real issue we would break gravity up into Mg perpendicular to the ramp and Mg parallel to the ramp where this angle here was this angle here I think Mg parallel often ended up being cosine and sorry perpendicular often ended up being cosine and parallel often ended up being sine but do the trig your equation would look like this who's winning well this is six kilograms even if this was hanging straight down would it be winning next to a 10 kilogram mass and since it's not straight down it's partly level the 10 kilogram has to be winning so we would say this winner and I've decided down when I get here is winner so the first tension is loser but Aaron this second tension when I follow it across ends up being a winner yeah tension cancels I'd make some joke about relaxing when tension cancelled or something like that if I recall and then I have two loser forces I have minus friction and minus Mg parallel that equals M1 plus M2 times a M both a there's your equation tension cancels you would find the purpose of the parallel component doing a bit of trig friction is what times what mu times the normal force I don't know the normal force oh but look look look look look I know another force the same size as the normal force what Mg perpendicular minus Mg and you know what it's mass 1 mass 1 I should include that G parallel that equals a divided by mass 1 plus mass 2 and now Matt Dylan you'd be on to just doing the trade be sine and cosine that's a classic forces type of a question okay other ones they like to ask for forces so here's number three another two-body mass question this time it's a bit easier but as a twist they're asking you to find the tension to find the tension once you have the overall acceleration to find tension you would probably go to this because it's got fewer forces and you would go winner minus loser equals and since you're only looking at one mass M2 a and now you could solve for tension because you know M2 you know G and you just figured out a other good forces questions something like number 23 where they ask what distance will it move before it comes to rest you have to find the overall acceleration first and then I guess it's slowing down so you'd make the acceleration negative to make it slow down the final is 0 the initial is 7 and you could solve for D I think Vf squared equals Vi squared plus 280 the other one that I've seen can I find one here let me look be prepared for them to give you a question like this maybe with one mass but instead ask you to find mu the coefficient of friction so give you enough information that you know oh I can for example if this was sliding down the hill if they gave you be initial and be final and the distance you could say oh I can find the acceleration and if I know the acceleration I could solve for mu as well so going forwards or backwards metallic on forces okay that's going to be the first question on the written forces or kinematics oh also kinematics up here for kinematics don't don't don't forget the last question on the review that was where we had the cannon hitting a wall at a certain height and we asked how far what was the range or something like that that one showed up more often recently okay so lesson 1 and lesson 2 are combined as are lesson 3 and lesson 4 so that was what shows up on the test 1 2 energy and momentum energy and momentum what are classic written questions on energy and momentum definitely one of the favorite ones is collision at an angle like number one here okay this is where you had to realize that you were doing vectors and this is where we found the cosine law really Sean and then to find an angle it was often sign law so make sure you look at those now this one's a bit of a twist instead of giving you the initial velocity they gave you the initial kinetic energy but if you know the mass and you know the kinetic energy can you find the initial speed it's a half MV squared square root right the other ones they like are these type of conservation of energy questions like in number two kinetic energy initial plus potential energy initially equals kinetic energy final plus potential energy final now I've been very very careful the questions that you're going to see on your mocks are either from provincial exams that you've never seen that are no longer available online that also haven't showed up on any of the views that I gave you or their questions that I've typed up myself and spent the time doing the graphics to do or they are questions from old Alberta provincial exams so look at your reviews but be prepared for oh I haven't seen that specific type of that specific question before you'll have seen that type of question before okay momentum collision the last one is like number three where they give you a collision now it's all linear so you don't have to do vector momentum but you have a change in momentum change in speed and then use potential energy at the end to figure out how high they go we did something like that on the review as well like I think I had one like that on your cast can't remember now so energy and momentum be alert for collisions if they are at angles use vectors and cosine law was the most common one explosions the initial momentum is zero so the final vector triangle comes back on itself right it was a close triangle where you ended up back where you started from if we had three pieces coming out of an explosion okay and then for energy conservation of energy kinetic energy initial plus potential initial equals to the final plus potential energy final and the work energy theorem which was work equals change in potential plus change in kinetic you guys can write the deltas but I don't know where the delta symbolism this program and often not always metallic but often one of these change in was zero just to make it easier last thing squared the number of dumb mistakes we made in this unit because it's a half MV squared and we either forgot to square it or when solving for be we forgot to square root that's gonna be your second written question your third written question it's going to be equilibrium probably torque so let's do one since I've had a request so there was two types of equilibrium questions there was one like this and a question like this are there is there a beam no so you would say use forces and you would say to yourself self oh heck mr. do it copy and clip it what are the forces acting on this get get the obvious ones and then we have tension one and tension to Kyle is this thing accelerating at all what's my net overall force then how does that show up in my diagram now I have three forces I always draw the easiest one first this one then I always draw the yuckiest one next I think the yuckiest one is this one here and then I draw the third one but because the tally the force is zero what this means is my vector has to come back to where I started from that's what zero looks like as a vector and this question says the tension in cable 2 is how big 12,000 I gotta do now is find some angles well let's see how big is the angle between mg and tension one how big is that angle right there can you read that Troy and how big is this right here so you know what I think it's a hundred and twenty degrees right there I'm not quite sure what this is but this is next to a vertical line here is next to a vertical line how big is that angle right there oh I see a Z see it now this angle up here is 20 degrees so every triangle adds to 180 this angle down here is 40 degrees and now because I have a pair right here I can use the sign law what I want me to find they want me to find mg the weight of the wrecking ball sign of that over that equals the sign of this over that so that's one type of written question but you guys really wanted me to do a torque question you wanted me to talk about torque tough audience yet I am something like number four a uniform blah blah blah blah blah blah blah blah is there a beam torque let's label all the forces on this beam and if this was a small diagram I would redraw it really huge but this is a pretty big diagram what are the forces acting on this beam get the obvious ones okay which always goes center of mass right about there that's going to be the mass of the beam times G then I also have M1 G and then I have tension the problem is none of these are perpendicular to the beam oh by the way there's probably a force here because I'm seeing two downwards forces and no upwards forces I'm sure there's a big force there but I'm gonna put my pivot there so no torque so who cares oh and I'm seeing a force to the left which also means this guy is also probably pushing to the right who cares it's right by the pivot area so no torque but to do torque we had to break everything up into perpendicular components torque was the perpendicular force I'm running out of room here a little bit so let's do this this is M1 G perpendicular and tension perpendicular coming back to you a little bit Alyssa we then said what did we write on every torque question what was our standard approach give you a hint the sum of all the torques clockwise in this direction equals the sum of all the torques counterclockwise in that direction clockwise what would cause it to spin around the hinge right there this way ah tension perpendicular right times its distance from the pivot which is 2.4 equals counterclockwise M1 G perpendicular times its distance from the pivot which is 2.4 minus 0.5 1.9 plus the mass of the beam G perpendicular times its distance from the pivot which was oh center of mass 1.2 okay how would I get tension perpendicular by itself okay then I would carefully do the trig both of these are going to be sine or cosine I'll let you try that yourself that would give you tension perpendicular I would put that there and I would do the trig here oh by the way this angle is 35 degrees so oh this is a tough one let's turn on my use pen as pointer that's this thing right here right ready how big how big zed how big 90 minus 35 how big 35 that's 35 and that's 35 up there what about in my tension triangle oh okay how big 35 now I've got a zed 35 who knew that high school grade 11 geometry would come in handy is that enough of a because I'm running out of time is that enough of a review okay then we come to circular motion gravitation what kind of questions can you at expect orbit orbits yeah I feel like I'm gonna die it's an orbit no orbits obrits good gosh or bits okay fc equals f net questions note and I still saw this on the magnetic forces test that we haven't gone over that I could have gone over today and just thought of that right now but that's okay I still see this I still see this f equals V well I'll just write it I'm still seeing f equals V squared over our garbage that's never been a force look on your formula sheet what is V squared over our acceleration how can I make an acceleration into a force apparently I forgot to turn that thing off also note if in space station normal force equals fc in a space station that was rotating it was the normal force that worked out to your centripetal force we said that centripetal force was always your net force it never shows up on the free body diagram it shows up in the winter minus is equals something okay also for orbits work energy orbit questions how much work to lift something up remember work is change in kinetic plus change in potential but now we had to use the cosmic potential which was negative big g big m the lem over r squared then there is going to be an electrostatic question voltage electric field all that good stuff then there's going to be a circuitry question magnetic forces or induction question they're technically the same unit then there's going to be a analyte come on mr. do it analyze a graph question that's number eight it's either going to be the slope or the area if it's a slope divide the formula or divide the units to figure out what the heck the slope is if it's an area multiply the variables or multiply the units to figure out what the area is and then the very last written question is going to be a using principles of physics right to explain question that's the written nine questions to get a good idea of what it's going to look like look at the four exams that I gave you there's some of them are still sitting here and you'll notice they all follow that pattern you'll notice oh yeah number five is electrostatics almost every time oh yeah number seven is magnetic forces almost every time which also means you can kind of figure out what topic you're in by what number you're on which might help you look at a certain spot on the formula sheet if you want to go through your magnetic forces test I am around today after school I am around tomorrow after school I'll be in Wednesday morning at like eight I'll be in at lunch as well but that won't help you because you guys are writing before like no you guys are writing after lunch so I'll be in my room Wednesday at lunchtime if you have any induction questions if you need me to induce knowledge out of induced voltage that it is