## dessyj1 one year ago What are the units of the energy of a photon and the energy of light? I know light intensity is the number of photons that corresponds with the wavelength so from the information I would guess the unit would be number of waves per second.

1. anonymous

Energy of a photon=hv h=Planck constant. Its units are J*s or joules times seconds v=frequency. Its units are 1/s Energy of a light is energy of photon, since photon is a packet of light. Do you mean speed of light?

2. dessyj1

I understand now. I was never given the units to Planck's constant. I was just give a number.

3. anonymous

The question is just asking for units Planck constant is 6.626 x 10^-24 J*s btw

4. dessyj1

Yeah, i was not shown the j*s - i was only shown the number. So when i would do calculations with planck's number the units would not cancel completely because i did not know the j*s.

5. anonymous

You do not need numbers to figure out the units. I give you explanation, but not the answer. (I know the answer) You can figure the answer by my info. Example problem: Velocity=distance/time Units of distance=m Time=s Velocities units would be m/s Just wondering if you can figure it out.

6. Photon336

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

7. dessyj1

I understand what you are saying. I did not know the units for planck's constant so when I would try a practice problem like this one, it would go like this. What is the energy of a photon of green light with a 520nm wavelength? $E _{p}= \frac{ hc }{ \lambda }$ $E _{p}= (6.626x10^{-34})(2.998x10^{17}nm/s)(\frac{1}{ 520nm })$ so, at the end of the day I would be left with a unit of 1/s(which did not make sense to me) because I did not know the full mangitude of planck's.

8. anonymous

Do you know the units for the energy of a photon now? If you do, then I can continue to solving problems with you.

9. dessyj1

Yes, it is in joules.

10. dessyj1

If I modified the question and said there were 10 photons in the wave, what would be the answer.

11. dessyj1

Are photons measured in mols?

12. anonymous

You are right. It is in joules. Modify which question?

13. dessyj1

What is the overall energy of green light with a 520nm wavelength that contains 10 photons?

14. anonymous

You would multiply it by 10 since ten more photons means then more energy. E=hv/wavelength only applies to one photon

15. anonymous

ten more energy*

16. dessyj1

would the units still be just joules?

17. anonymous

Yes. Lets say a photon has an energy of 500J 10(500J)=5000J

18. dessyj1

Okay. Thank you!

19. dessyj1

How would you measure photons?

20. dessyj1

Or is it very discrete?