# Homework Help: Finding the magnitude of electric field

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1. Jul 12, 2017

### jlmccart03

1. The problem statement, all variables and given/known data
A uniform electric field exists in the region between two oppositely charged parallel plates 1.59 cmapart. A proton is released from rest at the surface of the positively charged plate and strikes the surface of the opposite plate in a time interval 1.50×10−6 s .

Find the magnitude of the electric field.
Use 1.60×10−19 C for the magnitude of the charge on an electron and 1.67×10−27 kg for the mass of a proton.

2. Relevant equations
Coulomb: F = kQq/r2
F=ma
F=qE
E=kQ/r2
a=F/m

3. The attempt at a solution
First I have taken this course last spring and failed it. I simply do not understand how I set up these problems and get answers without being given an example. I literally bang my head against my desk and now I am doing the exact same thing just in a new semester. So I attempted to solve the problem this way.

I took E=kQ/r2 thinking that I could simly take the magnitude of Charge times Coloumbs constand divided by the distance squared. I get this E = 1.60*10-19 * 9*109 / 0.01592 to get 9*10-8 N/C. It's wrong. So I looked up a way to do this problem by Googling how to find electric field between two planes. I get E = V/d, but that is something we haven't learned yet so I think I am missing something and simply do not know where to go. How do you find electric field magnitude with the given equations? More so, how can I learn to tackle these problems since I just keep going one after the other not knowing what to do?

Thanks for any and all help given!

2. Jul 12, 2017

### NFuller

This is the electric field around a point charge, which is not relevant here.
You should first find the equation for the force on a charge. Once you have this, you can work out the needed variables from F=ma and the one-dimensional motion equations.

Last edited: Jul 12, 2017
3. Jul 12, 2017

### NFuller

We've all been there...
There's no simple answer. My best advice is to try and understand the meaning of the formulas and their relation to reality as thoroughly as possible. Once you do that, it is just a matter of algebra. The biggest mistake you can make is to just try and memorize equations and hope they work.

4. Jul 12, 2017

### jlmccart03

I managed to figure it out all on my own!!! And yeah I struggled last semester. I going to see my professor and TA's to see what I can do to make sure I understand the material. It's possible, I know I can do it, it just takes time and persistance to fight for an A in the class, but better an understading of how to do physics. Thanks!

5. Jul 12, 2017

### Universeer

I guess this will help.