# Quantinzation of Energy & Planck help!

1. Jan 5, 2006

### hshphyss

Can any one help me with this question? Thanx

Calculate the frequency of the photon emitted when an electron in an atom changes from (-2.42e-19 joules) to (-21.76e-19 joules).

I know that i'm going to use E=hf and h=6.63e-34. I'm not sure what I do with the 2 enery levels, do i subtract them?

2. Jan 5, 2006

### Pengwuino

A photon is emitted when an electron falls into a lower energy level. The photon must equal the difference in energy due to conservation of energy. E will equal the difference in energy levels. You can then use algebra to determine f, the frequency.

3. Jan 5, 2006

### hshphyss

Electromagnectic Wave Help

Can anyone help me with this problem?

What is the wavelength for an FM radio signal if the number on the dial reads 98.5 MHz? C=3e8

I know that c=f wavelength, and MHz is a million hertz I thought I could do 1E6 x 98.5=9.85e7 and then I could just solve for the wavelength with 3e8=9.85e7wavelength but I keep getting the wrong answer. Am i missing something??

4. Jan 5, 2006

5. Jan 5, 2006

### hshphyss

My mistake I got that one it is 3.05. But another where there frequency is 25 GHz. To find the wavelength on this one i would 3e8/25e9=0.012, and that is wrong. Thanx

6. Jan 5, 2006

### Pengwuino

If its 25 ghz... then 0.012m is correct...