# Homework Help: Calculating work done by an electric field

1. Sep 7, 2008

### crh

1. The problem statement, all variables and given/known data

How much work does the electric field do in moving a proton from a point with a potential of +155V to a point where it is -75V. Express your answer in both joules and electron volts.

2. Relevant equations

W = -qV

3. The attempt at a solution

I know that q=(1.6E-19) but I am not for sure how to go about incorporating my two potentials. Can someone give me some help? I thank you in advance!

2. Sep 7, 2008

### Hootenanny

Staff Emeritus
Perhaps it would help if the equation was written thus:

$$W = -q\Delta V$$

In other words, the work done by the electric field on the charged particle is the negative product of the charge and the change in potential.

3. Sep 7, 2008

### crh

Ok I think I figured it out. Tell me if I am wrong.

W = -qV, but V is potential E (PE), so therefore V = (PE2-PE1)

so...

W = -(1.60E-19C)(-80V) = 1.28E-17 J
and
= -(1e)(-80V) = 80eV

4. Sep 7, 2008

### Hootenanny

Staff Emeritus
You're on the right lines but be careful when calculating the change in potential.

5. Sep 7, 2008

### crh

Are you meaning scientific notation?

6. Sep 7, 2008

### Hootenanny

Staff Emeritus
Nope, something somewhat simpler than that. What is the difference between -75 and +155?

7. Sep 7, 2008

### crh

oh it needs to be -230V.

8. Sep 7, 2008

### Hootenanny

Staff Emeritus
Much better