# What is the magnitude of the electric field

1. Jan 21, 2010

### shimizua

1. The problem statement, all variables and given/known data
A cat rubs her back on the carpet, and acquires a net charge of -54.1 uC. What is the magnitude of the electric field at a distance 4.01 m from the cat?
and
What would the magnitude of the electric field in the previous problem be,
if the distance from the cat were now tripled?

2. Relevant equations
F=kq/r^2

3. The attempt at a solution
F=8.9E9(54.1E-6)/4.01^2
my answer came to 2.86E4 N/C which is wrong.

obviously i should be able to get the second part once i understand what i am doing wrong in the first part

2. Jan 21, 2010

### doive

You have calculated the force due to the electric field, not the field itself.

I believe the eq you are looking for is:
$$E=\frac{Q}{4\pi\epsilon_0r^{2}}$$

3. Jan 21, 2010

### tiny-tim

it shouldn't … did you enter 8.5 instead of 8.9?

(and isn't it 8.988, or just 9.0, anyway?)

4. Jan 21, 2010

### shimizua

k so i did

E=54.1E-6/4*3.14*8.85E-12*4.01^2 and got 2.7E4 N/C which still was wrong. what else did i do wrong?

5. Jan 21, 2010

### shimizua

Never mind I got it. i was using the right equation, lol i guess i did just enter a number in wrong. funny cause i did it like 10 times. thanks though tiny-tim