# Joules - Quanta

1. Apr 24, 2005

### Jacob87411

Hey I am in need of some assistance. In a problem I need to transfer Joules to quanta but am unsure on how to do it. A radio station is going at 200 KW with a frequency of 103.7 MhZ. So 200,000 Joules a second need to be converted to quanta. Thanks in advance!

2. Apr 24, 2005

### Andrew Mason

You want to find the number of photons (radio frequency ones) emitted per second.

Start with $$E_{photon} = h\nu$$

The total energy in one second is equal to the sum of the energies of all the photons emitted in one second. I think you can work the rest out.

AM

3. Apr 24, 2005

### Jacob87411

Is the E=hv the sum of the energy for all the photons?

4. Apr 24, 2005

### The Bob

No. This equation will give you the energy that is released in one photon.

5. Apr 24, 2005

### Jacob87411

Ah and then the total energy has to be equal to the 200 KW..but what is the speed on the photon? C?

6. Apr 24, 2005

### The Bob

You do not need the speed. You need Planck's Constant.

7. Apr 24, 2005

### Jacob87411

E=HV, yeah nevermind, meant F..thanks this one makes sense now

8. Apr 24, 2005

### Andrew Mason

So how many photons are produced in one second?

AM

9. Apr 24, 2005

### The Bob

Personally I get a rather large number (which is too be expected) but should it be this (2.9 x 1030 photons) big???

10. Apr 24, 2005

### Jacob87411

I got a huge number as well..It is large but I expected it to be of such size

11. Apr 24, 2005

### The Bob

Was it the same as my number???

12. Apr 24, 2005

### Jacob87411

You didnt give a number :)

13. Apr 25, 2005

### The Bob

It was in white.

14. Apr 26, 2005

### Andrew Mason

It is that big. At 1000 km, the intensity would be about 2 x 10^17 photons/m^2 per second. And that is just a measly radio antenna. You can see why a quasar can still provide detectable radio signals on earth despite being billions of light years away.

AM

15. Apr 26, 2005

### The Bob

You can. So much for telescopes that can detect a few photons of light, use radar discs.