Calculating Electric Field Strength for a Point Charge and Proton Interaction

[TomM]

Homework Statement

(This was part of an assignment that we had to create, so the question is one of my own, although I'm not quite comfortable with this area, hence why I'm asking for help) Calculate electric field strength of a positive point charge of 1.3x10-7C that is 5.3x10-4m away from a proton (+1.6x10-19C).

Homework Equations

[PLAIN]https://www.physicsforums.com/latex_images/25/2542612-1.png

The Attempt at a Solution

As put into calculator:
(9e9)*(1.6e-19)*(1.3e-7) = 1.8e-18

(5.3e-4)^2 = 2.8e-7

(1.8e-18)/(2.8e-7) = 6.4e-12

6.4e-12 = Electric Field Strength?

 

[eczeno]

your question does not quite make sense. the electric field is a vector quantity that is assigned to locations in space, not to things like charges. The calculation you have done yields the electric force between the two charges, not the electric field.

 

[TomM]

your question does not quite make sense. the electric field is a vector quantity that is assigned to locations in space, not to things like charges. The calculation you have done yields the electric force between the two charges, not the electric field.

Ok, so I should change the question to electric force? Or am I missing part of a calculation to give me electric field strength. Because, I've had trouble with this unit in my class for a while and I want to understand it. Isn't there a way to get electric field strength from electric force?

 

[eczeno]

if you change the wording to electric force, everything works out and your calculation is correct.

if you would like to strengthen the question, and understand electric field a little better, let me suggest making it a two part problem.

1) what is the magnitude of the electric field a distance 5.3x10^-4m away from a proton?

this is a good way to see that the electric field is a property of a location in space. the electric field tells us what the force will be if we put a charge there, all we have to do is multiply it by that charge.

So, if the electric field is E at some point in space P, and you put a charge q at that point, it will feel a force F = qE.

That leads to part two of the question:

2) what force will a 1.3x10^-7C charge feel if put at this location?

cheers

 

[TomM]

if you change the wording to electric force, everything works out and your calculation is correct.

if you would like to strengthen the question, and understand electric field a little better, let me suggest making it a two part problem.

1) what is the magnitude of the electric field a distance 5.3x10^-4m away from a proton?

this is a good way to see that the electric field is a property of a location in space. the electric field tells us what the force will be if we put a charge there, all we have to do is multiply it by that charge.

So, if the electric field is E at some point in space P, and you put a charge q at that point, it will feel a force F = qE.

That leads to part two of the question:

2) what force will a 1.3x10^-7C charge feel if put at this location?

cheers

Thanks! But, I'm still a little confused on how i would find the magnitude of the electric field. Would i do F=(kq)/r^2 rather than multiplying both 1.3x10^-7, 1.6x10-19C and 9x10^9?

 

[eczeno]

yes, the magnitude of the electric field a distance r from a charge q is: E = kq/r^2 . (but call it E, not F, it is not a force).

to find the force another charge, Q, would feel at a distance r from q, multiply the field and the charge Q:

F = QE = kQq/r^2

 

[TomM]

yes, the magnitude of the electric field a distance r from a charge q is: E = kq/r^2 . (but call it E, not F, it is not a force).

to find the force another charge, Q, would feel at a distance r from q, multiply the field and the charge Q:

F = QE = kQq/r^2

THANK YOU so much, i really appreciate it! I finally understand this, and I've been working on this in class for a couple weeks. Your great!

 

[eczeno]

cheers