# What Affects the Energy of a Photon?

1. Jun 20, 2010

### FeDeX_LaTeX

Hello;

I asked my physics teacher what affected the energy of a photon. He said that it was only the frequency, and nothing else. However, I don't understand this.

E = hv (I'll say E = hf to make it simpler to avoid confusion) states that the energy of a photon is equal to Planck's constant multiplied by the frequency of the wave.

However, frequency is equal to velocity over wavelength due to v = fλ. So this means that;

$$E = \frac {hv} {\lambda}$$

Meaning that frequency, wavelength AND velocity affect the energy of a photon. Is this true or is my physics teacher correct?

Thanks.

2. Jun 20, 2010

### antibrane

I would say your teacher is correct. Assuming the photon is in a vacuum, it always travels at the speed of light, c. Then you know,

$$c=\nu\lambda$$

so if I give you the wavelength of a photon, you automatically know what the frequency is--they are dependent on each other.

3. Jun 27, 2010

### FeDeX_LaTeX

Thanks, that makes sense. So it is definitely only wavelength and frequency (and photons per second) that affect the intensity of light?

4. Jun 27, 2010

### johng23

Photons per area per second, otherwise yes.

5. Jun 27, 2010

### cragar

If i were to travel at the photon at a certain speed , the Doppler effect would come into play and i would perceive the photon as a different frequency so if i traveled fast enough i could make red light look green , i wonder if that would hold up in court for blowing a red light , then they would just give me a speeding ticket anyway , And also gravitational fields affect the frequency of the photon ,

6. Jun 27, 2010

### HallsofIvy

Well, if they don't fine you for running through the red light, they could certainly fine you for speeding!