# Homework Help: Photon momentum and energy question

1. Nov 6, 2012

### metalrose

1. The problem statement, all variables and given/known data

Choose the correct option (only one correct option)
Two photons having
A.) equal wavelengths have equal linear momenta
B.) equal energies have equal linear momenta
C.) equal frequencies have equal linear momenta
D.) equal linear momenta have equal wavelengths

2. Relevant equations

λ=h/p
E=pc
f=c/λ

3. The attempt at a solution

All options seem correct to me. But the correct answer given in my book is the option d.)

Looking for an explanation for why the other three are incorrect.

2. Nov 7, 2012

### Simon Bridge

linear momentum is a vector.
wavelength, energy, and frequency, are not.
All are correct if they said "equal magnitude".

3. Nov 7, 2012

### metalrose

Thanks a lot. I don't know how overlooked that ..!!

4. Nov 7, 2012

### Simon Bridge

Actually it took me a little while longer than I'd have liked.
And it is because of how we are used to seeing those equations.
Cheers.