# AP Physics 1: Electrostatics Review

mr.p: Good morning. Today we are going to review
the electrostatics topics covered on the AP Physics I exam. Bo: Hey guys. Billy: Hey Bo.
Bobby: Hi Bo. ♫ Flipping Physics ♫ mr.p: Let’s start with the concept
of the elementary charge. 1.6 times 10 to the negative 19 Coulombs. It is called the elementary charge, because it is the smallest
charge ever to be isolated. Two examples of particles
with this magnitude charge are the proton and the electron. They both have the same magnitude charge, the elementary charge; however, the electron
has a negative charge, and the proton has a positive charge. The electron is a fundamental
particle; the proton is not. The proton and the neutron
are made up of quarks, more specifically up and down quarks. A proton is composed of two
up quarks and one down quark, and a neutron is composed of one up quark and two down quarks. Because the charge on an up quark is equal to positive 2/3
times the elementary charge, and the charge on the down quark is equal to negative 1/3
times the elementary charge, the net charge on a proton
is equal to the positive of the elementary charge, and the net charge on the neutron is zero. [Bo] Hold up, Mr. P.
Mr.p: Yes, Bo? Bo: I thought you said
nothing could have a charge less than the elementary charge. Billy: Yeah, a quark has a charge less than 1.6 times 10 to the negative 19 Coulombs. That doesn’t make any sense. Bobby: Actually, what he said
is that no isolated charge can have a charge smaller
than the elementary charge. Right? mr.p: Correct, Bobby. A single quark has never been isolated. We’ve never found a quark by itself. They’re always found in groups, like they are in the
proton and the neutron. Okay, next let’s talk
about the Law of Charges. Bobby, what is the Law of Charges? Bobby: Umm. Billy: Unlike charges attract. Bobby: And like charges repel. That’s right. mr.p: Therefore, if we have two like charges, two positive charges, for example, they will repel one another. And if we have two
charges that are unlike, positive and negative,
or negative and positive, they will attract one another. And if we have two negative charges, they are again like charges, and they will repel one another. The magnitude of this force can be found using Coulomb’s Law. Coulomb’s Law gives us
the electrostatic force that exists between two charges. k is called Coulomb’s constant, and has a value of 8.99
times 10 to the ninth Newtons times meters squared
divided by Coulombs squared. q1 and q2 are the charges of
the two particles, and r… Well, actually, let’s bring
up a similar equation, so that we can talk about the value of r. Newton’s Universal Law of Gravitation, what I like to the Big G equation. Notice the similarities. We have Coulomb’s constant instead of the universal gravitational constant, and we have charges instead of masses; however, we have the same r, which means, class, r is not? All: The radius. mr.p: r is? All: The distance between centers of charge of the two charges. mr.p: This can be confusing,
because sometimes r is? All: The radius. Bo: Again. mr.p: Correct, r is defined as the distance between the centers of
charge of the two charges. Now, Coulomb’s Law functions very much like Newton’s Universal
Law of Gravitation, but it is very important to underscore the difference in magnitudes
between these two constants. Coulomb’s constant is
times 10 to the ninth. Universal gravitational constant is times 10 to the negative 11th, which means that Coulomb’s constant is approximately times 10 to the 20 greater than the universal gravitational constant. Which means, typically,
the electrostatic force is much, much, much greater than the gravitational force. Okay, now let’s talk about
conservation of charge. Charge is conserved in an isolated system. For example… Let’s say we have two spheres that are electrically isolated
from everything else. The net charge on the first sphere is positive four Coulombs. The net charge on the second sphere is negative two Coulombs. We’re going to touch those
two spheres together, and then separate them,
and the question is, what are the final net charges
on each of the two spheres? Billy? Billy: Well, the system is isolated, so the total net charge will be conserved. Therefore, the total net charge is positive four plus negative two Coulombs, or positive two Coulombs. That’s the total net charge. I’m not sure what the net charge on each sphere will be though. Bo: Remember, like charges
repel, so it will balance out with half the total charge on each sphere. Billy: Oh, so then each sphere
will have a net charge of positive one Coulombs
after we pull them apart. Bobby: Does that mean that each
sphere will have a total of 1.6 times 10 to the 19 protons on them? mr.p: Actually, no, Bobby. Each sphere doesn’t end with
1.6 times 10 to the negative 19 protons on it. Let’s figure that out. The net charge on one of the spheres is going to be equal to
excess number of charges on that sphere, multiplied
by the elementary charge. Which means, the excess number of charges on one of the spheres
is going to be equal to the net charge on that sphere, divided by the elementary charge. And because the net charge
on each of the spheres is positive one Coulombs, we can divide that by
the elementary charge, with more sig figs, 1.6022
times 10 to the negative 19 Coulombs per proton, and
that gives us approximately 6.24 times 10 to the 18th protons. Bobby: Oh, right, sorry. Each sphere will have a total of 6.24 times 10 to the 18 protons. mr.p: Actually, no. Each
sphere will have an excess of 6.24 times 10 to the 18th protons. Each sphere has a heck of a lot more protons and electrons than this. It’s just that each sphere has 6.24 times 10 to the 18th more protons than it does electrons. Bobby: Right, that is not just
the sphere’s electric charge. It is the net electric charge. Billy: Wait, there was only one sig
fig on positive one Coulombs, so our answer should only
have one significant digit. Bo: Yeah. mr.p: We have reached the end of my review of electrostatics for
the AP Physics I exam. My next review lesson is about electricity. You are more than welcome
to enjoy that video. You may also visit my website, flippingphysics.com where you will find all of my AP Physics I review lessons, organized with lecture notes. Thank you very much for
learning with me today. I enjoyed learning with you.

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## 41 thoughts on “AP Physics 1: Electrostatics Review”

1. Flipping Physics says:

Electrostatics Review for AP Physics 1. The tenth in my set of AP Physics 1 review videos. Enjoy! #PhysicsED #flipclass #APPhysics1

2. Leo Tonozzi says:

Thanks man!

3. PapaHance says:

These need more views. You are the reason I'm doing well in AP Phys!

4. alvaro Montero says:

Thank you Mr.P!!

5. Sergio Momo says:

This is a great review based on that it is concise while giving all info needed. Not to mention that its not boring. Thanks!

6. AlanmanAaron says:

What about leptons in electrons? These are great btw, love it

7. Deniz Akıncı says:

I don't usually comment on videos but I just wanted to say that you are the man for uploading these videos. You are fun to watch, deliver a lot of content and extremely easy to understand in just 10 minutes. This deserves a lot more views. One of the best teaching channels in youtube !

8. OB Trice says:

A little goofy, but this really helped me a lot, especially since the AP Test is this week. Keep up the good work!

9. Erica Hu says:

Thank you Mr. P, and the exam is tomorrow!!

10. Nick Navarro says:

11. John Decker says:

Thank you!! These videos really help with IB Physics too! Bless your soul

12. silvia mathee says:

All this videos are, legit the reason I pass all my exams! thank you.
#physicsmajor

13. Abhay Gautam says:

nice look☺

14. baggerz 123 says:

you have to give this guy credit, thanks for the videos

15. Remi Klein says:

You are saving my life. Thank you so much!!

16. Rick Evans says:

Great teaching video!

17. Diego Zablah says:

Hi mr. P! I have used your review videos for this years exam, and they have been very helpful. But i have a question on this topic. Are charges dependent on mass? For example if you have two spheres of equal charge and mass m, and one mass is increased, will the charge in that sphere change?

18. I'm Infamy says:

This is legit done so well. Covers the content needed without excess, does it quickly, and does it clearly.

19. 22Tech says:

much much M U C H

20. Jas Jakowski says:

Keep Posting. Great videos!

21. Varda Singh says:

My exam is tomorrow and my teacher never went over this T_T

22. DJ AB Slowed and Smoothed says:

10 minutes until the exam

23. Ralph Zurita says:

I really wish i had watched these while reviewing for my AP Exam…. Oh well, at least I'm confident about my final tomorrow.

who else came to see girl teacher?

25. Riana kristi says:

Thank you so much 😄

26. Chewii Cok says:

yeah….

27. Davis John says:

Thanks a lot Mr.P, this was confusing to me before, but now it makes sense. Thanks!!!

28. Udgey says:

I kind of got lost in the last few minutes. Thanks for these videos though! My AP exam is tomorrow.

29. Jacforse says:

On the actual AP test, we won't need to know anything regarding quarks, right?

30. Tedi Dimmer says:

This was by far the hardest unit for me to understand , so in a last ditch effort I clicked on the video. I'm so glad I did though! This helped me so much!

31. D SINGH says:

Is this also beneficial for cbse board?(India's Delhi board)

32. D SINGH says:

Sir can u plz provide me the link of chp.s from electrostatics to optics ….on jee curriculum (cbse) ….plz reply if yes or no

33. D SINGH says:

Sir can u recommend any chemistry channel like yours of phy.(the best)

34. jt132 says:

Whoops I’m in ap physics c this is way simpler and has 0 calculus

35. Laniakea says:

Editing on point

36. CHANGMIN PARK says:

Mr. P, I hope to see more of your videos about Electrostatics and Electricity since I am having the AP Physics 1 exam very soon!

37. Itschlobro says:

Bobby always flexin on us

38. PandazHub says:

Thanks for these videos 🙂 they're funny, informative, and high quality. Cheers for the ap tommorow!

39. aryan chowdhury says:

Exam tmrw let's goo

40. William Rooke says:

Some people have commented the day before… I am 4.5 hours out boys!

41. gbc hellboy says:

can u subscribe to my channel plz??