# Photon energy and calculating frequency

1. Jan 27, 2015

### MathiasArendru

Hello guys, im having a bit of trouble with some homework

So im told that a photon in a light beam has an energy og 2,12 eV. First i have to calculate the energy of it in joules, and since 1 eV is 1,60*10^-19 Joules 2,12 eV in joules is just 2,12*1,60*10^-19 = 3.392*10−19 J i got that.
Then i have to calculate the frequency of the light beam. I use the equation E = hv and just isolate v to get v = e/h. When i then plug in the numbers i get v = 3.392*10−19/6.63*10^-34(plancks constant) = 5.12*10^14 seconds. But isn't that a huuuge frequency? Anything i've done worng?

2. Jan 27, 2015

### MostlyHarmless

You shouldn't need to convert to joules. You should have a value for Planck's constant that is eV•s.

Also, if you're unsure what a reasonable frequency is, convert it to wavelength, and then see where that wavelength falls on the spectrum and compare that to the question. In this case if you convert to wavelength you'll find that this pretty much in the middle of the visible spectrum.

Last edited: Jan 27, 2015
3. Jan 27, 2015

### MathiasArendru

Actually you're right haha, when i first heard it, it just seemed like too much and i didnt think about it any further but obviously it is. and converting to joules was a task included in the assignment.
Thanks