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Ch 29: Magnetic Fields and ForcesWorksheetSee all chapters

# Magnets and Magnetic Fields

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Sections
Magnets and Magnetic Fields
Summary of Magnetism Problems
Force on Moving Charges & Right Hand Rule
Circular Motion of Charges in Magnetic Fields
Mass Spectrometer
Magnetic Force on Current-Carrying Wire
Force and Torque on Current Loops
###### How Magnets Work Concept:

Concept #1: How Magnets Work

Transcript

Hey guys. So, now we're going to start talking about magnetism and in this first video I'm going to keep it really simple and briefly explain to you how magnets work, let's check it out. Alright, so a long time ago, we found out that there«s some metals that would sometimes attract each other, they sort of magically get stuck, and this was first found in the Greek island of Magnesia, so these magic metals were called magnets. The metals that are most commonly, that most commonly have this magnetic property of getting stuck to each other are iron, cobalt and nickel but you should know that not all pieces of iron, cobalt and nickel are always magnetic, okay? Electricity and magnetism are very similar, there's a lot of analogies we're going to draw between the two. The first one here is that forces, electric forces can only exist between charged materials, meaning if you have two objects next to each other, they're only going to interact electrically if both of them are charged, if they both have charges, same thing with magnetic forces. So, you're gonna have magnetic forces if the two objects have this magnetic property. So, if you have two objects close to each other that are non-magnetic, you get no force, one magnetic and one non-magnetic you get no force and only in a situation like this you're going to get a magnetic force, very straightforward. Remember also the electricity, in electricity the forces could be attractive or repulsive, the same thing is going to happen with magnetic forces between magnets depending on the ends of the magnets, okay? So, let's say you have an iron bar here and then you have another iron bar here and when you bring them close to each other, they are attractive, they attract each other, there's an attractive force. Now, let's say you flip, you get the second bar and now you flip it, now you flip that bar and then you see that this force is actually now repulsive, so these guys will repel each other. And just from this observation, you can conclude that there must be two different types of sides, okay? Because the two sides are behaving differently, there must be two types of sides which are called magnetic poles. So, pole is just one of the sides of the bar. So, we could do something like, let's call the side A and B and then here with flipped and then this is going to be B and A. So, that's the first thing you need to know about magnets, is that they have two different sides, okay? Now, in electricity these sides were called, you had positive and negative charges and in magnetism these sides are going to be called North and South poles. Pole, again, is just a word for side or end of the magnet bar. You may remember that these names are arbitrary, positive could have been called good and negative could have been called evil or yellow or blue or whatever, but that's what they chose and same thing with North and South, this could have been called the positive side, could have been call the negative side but they chose North and South, so those are the names. And the last thing I want to talk about is what happens if you get two metals, two magnets that are identical. So, these guys here are same as left, what happens if you face different faces, different ends of the metal. So, if you were to get to two magnets and do this experiment, what you would see is that if you have the A side with the A side, these guys would repel each other, but then if you flip this and you have the A end or the A pole with the B pole they would attract, if you flip both so you have B and A they will also attract and finally, if you have B and B they would repel. So, hopefully you see a pattern here, which is that whenever the sides are different A and B, B and A they will have an attractive force and you may remember this from electricity, in electricity opposite charges would always attract, similarly in magnetism, opposite poles will also attract, cool? So, the same that opposites attract holds true for both electricity and magnetism and that's it for this one, let's keep going.

Concept #2: Magnetic Fields and Magnetic Dipoles

Concept #3: Compasses and Earth's Magnetic Field

Transcript