1. Sep 10, 2016

### Clara Chung

1. The problem statement, all variables and given/known data
Prove that the total energy of an electron orbiting a hydrogen nucleus is Etotal = -e^2/ 8ε0 π r where e is the magnitude of charge of an electron and r is the orbital radius.

2. Relevant equations
Knowledge

3. The attempt at a solution
Here is my attempt:
For KE,
mv^2/r = -ke^2/r^2
mv^2/2 = -ke^2/2r

For PE,
PE= k(-e)e/r - k(-e)e/∞
=-ke^2/r

2. Sep 10, 2016

### haruspex

Is the left hand side there positive or negative? What about the right hand side?

3. Sep 10, 2016

### Clara Chung

LHS is positive and RHS is negative? They should both be positive as the negative sign represents the direction?I don't get it

4. Sep 10, 2016

### haruspex

So the right hand side must be wrong. Try explaining in detail how you arrive at the minus sign there.

5. Sep 10, 2016

### Clara Chung

Thanks for helping me. But why the minus sign in potential energy need not to consider?

6. Sep 10, 2016

### haruspex

That is not an energy expression, it's a force expression.