# Homework Help: Energy in photoelectric effect

1. Dec 2, 2014

### Rishav sapahi

1. The problem statement, all variables and given/known data
Find the speed of light using planck's constant measuring apparatus

2. Relevant equations
E=h(frequency)
E=(h*c)wavelength

3. The attempt at a solution
Can I substitute E=mc2 and use the mass of electron in the equation?

2. Dec 2, 2014

### BvU

The template has "all variables and given/known data", but you have nothing there....

E = mc2 has to do with the total energy of an electron, moving or at rest. Is that what you have available as a known datum ?

3. Dec 3, 2014

### Rishav sapahi

No the known variables are only frequency , wavelength and planck's constant and I have to find speed of light.

4. Dec 3, 2014

### BvU

So your relevant equation should have been $c = \lambda \; \nu$ ?
($\nu$ = frequency)

5. Dec 3, 2014

6. Dec 3, 2014

### BvU

As I said,
The template has "all variables and given/known data", but you have nothing there....

So I don't know what are known values for you.

I don't really see how planck constant measuring apparatus can contribute in this context, unless you assume h is known and you use the instrument to determine $\nu$. Then you still need the wavelength...