# Accelerating electrons

1. Mar 6, 2007

### Gyroscope

1. The problem statement, all variables and given/known data
An electron is accelerated from rest through a potential difference of V volts. What is the final velocity?

I did:
$$qV=\frac{mc^2}{\sqrt{1-\frac{v_f^2}{c^2}}}$$

And solve for v, but I get an unreal answer. What am I doing wrong?!

2. Relevant equations

3. The attempt at a solution

2. Mar 6, 2007

### hage567

Why are you using relativistic energy?

3. Mar 6, 2007

### Gyroscope

Because there is an high potential difference. If I use non-relativistic energy it gives a speed higher than the speed of light.

4. Mar 6, 2007

### hage567

Could you post more of the question and your work?

5. Mar 6, 2007

If I'm not mistaken(Memory sometimes betray me) qV=(Gamma-1)mc^2

6. Mar 6, 2007

### Gyroscope

ziiad this is the relativistic kinetic energy, what I need is the relativistic change in kinetic energy.

7. Mar 6, 2007

### Gyroscope

No, you are right. What a stupid mistake of mine. :( Thanks, mate.

8. Mar 6, 2007