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### Course: MCAT>Unit 9

Lesson 13: Magnetism

# Magnetism - Part 4

Learn how magnetic force functions as a centripetal force. See how to calculate the radius of the path traveled by a proton. Explore some applications of magnetic force, including cathode ray tube (CRT) monitors and cyclotrons in particle accelerators. Created by Sal Khan.

## Want to join the conversation?

• Two things:
1. It would probably be better not to use a calculator in example problems since we cannot use a calculator on the MCAT.
2. Do these four videos on Magnetism cover all of the content concerning magnetism that the MCAT will test on? What about the magnetic fields caused by current carrying wires and how magnetic fields affect each other?

Keep up the good work!
• These videos have been up for years. They have been nicely organized to cover the MCAT content, but not all of them were specifically created for the purpose of the MCAT. You should check the AAMC website for an exact breakdown for the content you are required to know.

Make sure you do lots of practice on your own.. MCAT math is not simple math. The numbers are complex and ugly- this is done on purpose..it is supposed to be hard. Try pausing the video and challenging yourself to get the answer on your own without a calculator. Be sure to do lots and lots and lots of practice.
• Did Sal ever make a video about how TVs work?
That would be really interesting.
• If you look at the top left corner at you see Sal's most visited sites and it says "America's next top model" lOOOOOOol
I guess he is a fashion guru as well
• no calc on MCAT...
• Starting at about , I get a little confused as to how we would come up with the direction of the force on the electron using the right hand rule. I understood how we got the direction for the proton, and I understand that the direction of the force will be opposite of that of the proton since it's negative. But I don't know if I fully understand how we would find it if we did not already know the direction of the proton.
When using the right hand rule, we are using our pointer finger for the direction of the velocity, and we are using our middle finger for the direction of the magnetic field. Since those will still be the same, we will still have our thumb pointing downward, right?
So, it's only the fact that our force is negative that we change the direction of the force to the opposite direction? Is this correct? So, anytime we end up with a negative force, we automatically change the direction obtained from from the right hand rule to the opposite direction? Or is this only if we have a negative charge? In any case of having a negative force, couldn't we just use our left hand instead and get the right direction without having to change it?

Sorry if my explanations are long and confusing, I just want to know if I am understanding this part correctly. :)
• 1. apply the same concept with the left hand

or

2. use the right hand and take the opposite of the direction of the force you find.
• is there ever going to be a section dedicated to AP Physics C? I see that there is an AP Physics 1 and 2, and so i was wondering if there is going to be an AP Physics C in the future
• Hey khan academy, please stop using calculators when we can't even use them on the MCAT..
• As someone else has pointed out, this video was not created exclusively for the MCAT but was included in this playlist to help viewers gain a deeper understanding of the concepts.