# Find potential difference of negative charged particle?

1. Jan 22, 2012

### gibson101

1. The problem statement, all variables and given/known data
The work done by an external force to move a -8.5μC charge from point A to point b is 15x10^-4 J. If the charge was started from rest and had 4.82x10^-4 J of kinetic energy when it reached point b, what must be the potential difference between a and b

2. Relevant equations
W(nonconservative)=ΔKE+ΔPE
V=ΔPE/Q

3. The attempt at a solution
15x10^-4 - 4.82x10^-4 J= .001 J (Work = ke f - ke i (0) + PE f (0) - PE i) So PE i would equal -.001 J.
Then v= -.001J/-8.5x10^-6 C = 119.7 Volts.
But the answer is supposed to be -119.7 volts?

2. Jan 22, 2012

### technician

My first thoughts are that the question is badly worded!! A Potential DIFFERENCE is surely just a value ...119.7V
The negative charge starts from rest and gains KE which tells me that point A is a negative charge and the external force of the charge at point A repels the negative charge to point b
So point A is -119.7V with respect to point b

3. Jan 22, 2012

### gibson101

When we say potential difference what do we mean? My textbook defines potential difference as the work required to move a unit of electric charge from point b to point a.