# Mass of an accelerated electron?

1. Dec 30, 2012

### Tryhard2

1. The problem statement, all variables and given/known data
An electron is accelerated from rest through a potential difference of 31kV

2. Relevant equations
I don't know how to engage or solve a problem like this, I've done this attempt but i'm very uncertain that I've done it in a correct way, it's hard to understand if I've choosen correct forumulas etc it feels much like guesswork for me, but the final answer seem plausible as it is a small increase as it should, shouldn't it?

Have I done it right and have a good solution? if not, how do you solve such a problem?

My feeling was that if there is a mass while rest and another for acceleration I can add them together like this. But I'm not sure I have the right masses even.

3. The attempt at a solution
the electrons mass, m_0 = 9.109*10^-31 kg
Speed of light, c = 2.998*10^8 m/s

E=m_1*c^2 and E=QU give me:
m_1 = QU / c^2

m_1 = (1.602*10^-19) * 31000 / (2.998*10^8)^2 = 5.525*10^-32 kg

I then add m_1 and m_0 together giving me my final answer. m, m= m_0 + m_1
m = (5.525*10^-32) + (9.109*10^-31) = 9.66*10^-31 kg

Very thankful for input :)

2. Dec 30, 2012

### cosmic dust

This is OK! The electron gains energy qV , so total energy will be: E = m0c2 +qV = m c2 or m = m0 + qV/c2

3. Dec 30, 2012

### Tryhard2

when you say qV? is that QU? (columb times volt) or something else

so essentially I did what you describe in the end?

4. Dec 30, 2012

### cosmic dust

Yes

Yes, I just refered the reasoning for doing this...