# Simple electric field problem

1. Jan 12, 2008

### BuBbLeS01

Simple electric field problem....

1. The problem statement, all variables and given/known data
What magnitude charge creates a 4.17 N/C electric field at a point 9.78 m away?

2. Relevant equations

3. The attempt at a solution
E = (k * Q) / r^2
Q = (E * r^2) / K = 4.43 x 10^10 C
Why isn't that right?

2. Jan 12, 2008

### hage567

Check your math. I don't get the same answer with the expression you used.

3. Jan 12, 2008

### BuBbLeS01

oh shoot I was using K = 9 x 10^-9 because everything is in nC so thats what I did...thanks!!

4. Jan 12, 2008

### BuBbLeS01

Is this question not asking the same thing?

The electric field 4.1 cm from a small object points toward the object with a strength of 199400 N/C. What is the object's charge?

q = 3.72 x 10^-8 C

5. Jan 12, 2008

### hage567

If the field is pointing towards the charge, what does that tell you about the charge?

6. Jan 12, 2008

### BuBbLeS01

its negative

7. Jan 12, 2008

### hage567

Right. I don't see anything wrong with your calculation otherwise.

8. Jan 12, 2008

### BuBbLeS01

thanks so much!!