 How do you figure out the direction of the earth's magnetic field say in your room? How would you figure that out? Well, you might say let's just use a compass Here it's reasonable to think since the North Pole is pointing in this direction Maybe the magnetic field in my room is in that direction, but that did not be true This may not be the right direction. Can you pause and think a little bit about why that could be the case? Okay, the reason is because we are living in three-dimension and our compass needle is only allowed to spin in the horizontal plane So in this room our magnetic field could actually be pointing up like this at some angle and our compass would still show this direction Simply because the needle is not allowed to turn in the vertical plane Similarly, the magnetic field could also be pointing somewhere downwards below the horizontal Now this is not drawn properly. It's a little hard to see this from this angle So I can show you another angle if your compass shows this way your magnetic field can be above or below at some angle and This angle made by the earth's magnetic field with respect to the horizontal is what we call magnetic dip or inclination And if you think about it the name kind of makes sense It's basically telling you how much the magnetic field is dipping with respect to the horizontal So if the magnetic field is actually dipping downwards that this angle will call that as the positive angle And if the magnetic field is not dipping down but say it's you know, it's above the horizontal Then we can still say it's a dip we can call that as a negative dip So this could raise a lot of questions now and one of them could be how do you measure this magnetic dip at a point? Mainly because we just discussed in a compass the needle is only allowed to spin in the horizontal So a compass would be useless, right? But what you can do is you can just flip it and make it vertical and then see where the needle points in this example And it is pointing downwards. So you're giving some positive dip at this place, but I don't think this is very accurate I checked I tried and it gives you various different answers if you shake it mainly because there's a lot of friction over here It's not designed to give you the dip value and it's also extremely hard to keep your compass You know make sure that your compass is aligned vertically, right? So it's really hard to do that. So there are compasses built to actually measure magnetic dips Vertical compasses basically and they're called dip circles or dip needles. Here's an here's an example of that It's basically a compass in which the needle is only free to move in the vertical plane Another question or confusion that I always had was what's the difference between declination something We learned in the previous video and dip because both are angles. I'll just to recall declination gives you the angle between the direction of the true north pole or the geographic north pole and the magnetic field because magnetic field always points towards the Magnetic north pole. All right. So this is the angle in the horizontal So the angle between the magnetic field and the true north pole dip is the angle between the magnetic field and the horizontal itself so declination is the angle in the horizontal plane and Dip is the angle in the vertical plane and if you ever get confused just remember one dip is a very nice word It literally tells you how much the magnetic field is dipping with respect to word with respect to the horizontal So I remember that and I then I remember the declination is the other angle the horizontal angle Okay, now comes the most important question that you are thinking about is why should we care about magnetic dip, right? I mean declination value for example We spoke about that in the previous video and we saw how important it is for navigation With the declination value one can and and the compass you can now figure out where the true north pole is Where the geographic north pole is she's super useful for navigation, right to course correct yourself and everything But what about magnetic dip? Why would that be? Where would that be useful? But there are multiple uses for that one of the uses is even magnetic dip can be used to figure out where you are on the planet You can tell whether you are close to the equator or you're in the northern hemisphere or the southern hemisphere or you are close to the poles How does that work? How does the dip value help you in giving that? Well for that I have a question for you Here's the magnetic field of the earth something we saw in the previous video where we can imagine There is a giant bar magnet with its, you know magnetic poles reversed compared to the geographic poles What I want to do now what I want you to do now is look at this and Guess or actually try to figure out What would be the values of the magnetic dip at different parts of the world at the poles the equator The northern hemisphere and in the southern hemisphere and think in terms of whether it's gonna be a positive value or a negative value Is it gonna be a very high value or low value? So can you pause and think a little bit about this? All right, so what I like to do is pick a few locations and draw Horizontals over there Horizontals are drawn in the dotted lines which are basically tangent to the earth's surface, right? Now if you look at the poles You can see over here for example, not pole the magnetic field is pretty much vertically downwards meaning the dip is 90 degrees. It's positive because it's down Similarly, if you look at the south pole, it's exactly reversed the dip is negative 90 meaning it's dipping 90 degrees upwards So you know at the poles So if you ever find the dip to be close to 90 degrees, you know for sure you're at the poles Okay, what happens when you come closer to the equator notice the dip angle starts reducing So smaller the dip angle closer you are to the equator and close to the equator The dip is almost zero because the magnetic field lines are pretty much parallel to the ground Finally, how do you know whether you're in the northern hemisphere or the southern hemisphere? Well, notice in the northern hemisphere the dip is downwards. It's actually dipping below the horizontal So it's positive dip. In fact, let me draw the magnetic needles over there. It'll make it very obvious See now the hemisphere is you have positive dip values in the southern hemisphere It's the magnetic field lines are pointing upwards compared to the horizontal And so you have negative dip values So just by looking at the dip values, you can figure out Relatively where you are on the planet close to poles or equator northern or southern hemispheres incredible, isn't it Another super important use of the magnetic dip values is it helps us calculate the horizontal and the vertical Components of the magnetic field. Okay, what do I mean by that? So let's take an example Let's say we are somewhere in the southern hemisphere and the magnetic field is pointing upwards So this is the magnetic total magnetic field of the earth But most of the times when you're doing an experiment, let's say you're doing an experiment on a tabletop And where you want to use the field of the earth in that case, we don't care about the total field We only care about the horizontal Component of that field because that's the only field that's gonna affect our experiment in that case We want to know what the horizontal component is Similarly in certain experiments there we might be interested in figuring out what the vertical component of the magnetic field is right So knowing the dip value if you know what the total magnetic field value is you can figure these out And I want you to think a little bit about how to do that requires vectors and trigonometry And I think you have been introduced to both of them So let's say the magnetic field of the earth at some place where we are somewhere in the southern hemisphere Let's say over here is B. Let's just call the total magnetic field strength is B It's pointing upwards and let's say that the dip value is let's put some alphabet. Let's use I We're using I because D is used for declination already we're using inclination I so you know this and you know the total field Can you tell me what the horizontal value and the horizontal component and the vertical component of the fields are going to be? You can use this figure if you want. It's a little easier to see. This is the total field Let's say ignore the bottom one and I want us to figure out what the Horizontal component is going to be and this value is I this angle So can you pause and think a little bit about how do you calculate that? Okay, we may have learned in the about components in vectors and how do we take component? Well, we just drop a perpendicular From the tip of the vector on to the direction where we want to calculate the component And if you do that you can do that over here or you can do that over here Now you get a nice right-angled triangle where this becomes the hypotenuse and now you have to figure out what the adjacent side is Adjacent side is cos and so if you do a little trigonometry you will get pH equals the Earth's total magnetic field B times cos of what The declination or the dip of the dip dip is what matters to us And similarly the vertical component would be B times sine of I So it so the dip values the dip value helps us in figuring out the horizontal and the vertical components of the magnetic field Okay, so to put it all together to completely represent the magnetic field of Earth at any point We need three numbers three because we're in three dimensions So we have two angles the declination angle will tell us where the magnetic field is in the horizontal with respect to the north pole True north and the inclination will tell you how where the magnetic field is or dip will tell you where the magnetic field is With this in the vertical plane so the two angles will help us figure out lock Exactly the direction of the magnetic field and then we often like to represent the horizontal component of the magnetic field because that's most Often used that will tell us what the what the The magnitude of the magnetic field is so these three the horizontal component the declination and the dip are what we call the magnetic elements of Earth's magnetic field and if you know say the horizontal component You can figure out what the total magnetic field is and you can figure out what the vertical component is and so on and so forth