How Do You Calculate Electric Forces and Fields in AP Physics Problems?

[se1zure]

Hi, my name is Cory. I need a little help with one of my AP physics assignments, dealing with Electric Charge, Forces and Fields.

I got most of the problems, however here are a few I could use some help / be walked through on.

Problem 36)
On average, the electron and proton in a hydrogen atom are separated by a distance of (5.3 x 10 -11 m), assuming the orbit of the electron to be circular,
(a) what is the electric force on the electron? and (b) WHat is the electrons orbital speed? and (c) What is teh magnitude of the electrons entripetal acceleration in units of (g).
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I'm guessing I need to use fe = kqq
----
r^2
however, I'm not sure where rotational comes into play, nor how to do the rotational portion.
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Problem 55)
What would be the magnitude and the direction of a vertical electric field that would just support the weight of a proton on the surface of the Earth? of an Electron?


and lastly,

Problem 61)
What is the electric field at the center of the sqaure in the following figure:

 

[Decan]

For problem 36, you do need to use the equation listed to figure out the force on the electron for part a. Once you have the force, how can you relate that to the electrons speed and acceleration?

 

[m2003]

Hi Cory,

For problem 36, you're on the right track with using Coulomb's Law (fe = kqq/r^2). To find the electric force on the electron, you'll need to use the charge of an electron (-1.6 x 10^-19 C) and the charge of a proton (1.6 x 10^-19 C), as well as the distance between them (5.3 x 10^-11 m). The rotational aspect comes into play because the electron is moving in a circular orbit, so it is experiencing centripetal acceleration. To find the orbital speed, you can use the equation v = √(GM/r), where G is the gravitational constant (6.67 x 10^-11 Nm^2/kg^2) and M is the mass of the proton (1.67 x 10^-27 kg). To find the centripetal acceleration, you can use the equation ac = v^2/r. Make sure to convert all units to SI units before plugging them into the equations.

For problem 55, you'll need to use the equation F = Eq, where F is the electric force, E is the electric field, and q is the charge of the particle (proton or electron). Since the weight of an object is equal to its mass multiplied by the acceleration due to gravity (9.8 m/s^2), you can set F = mg and solve for E. Remember to use the charge of a proton or electron depending on which particle you are finding the electric field for.

For problem 61, you can use the equation E = kQ/r^2, where E is the electric field, k is the Coulomb's constant (8.99 x 10^9 Nm^2/C^2), Q is the charge of the particle creating the field, and r is the distance from the center of the square to the particle. You'll need to calculate the electric field at each of the four corners of the square and then use vector addition to find the total electric field at the center.

I hope this helps! Let me know if you have any other questions. Good luck with your assignment!