## 1.3

$\lambda=\frac{h}{p}$

FDeCastro_1B
Posts: 54
Joined: Thu Jul 25, 2019 12:16 am

### 1.3

In each second, a certain lamp produces 2.4x10^21 photons with a wavelength of 633 nm. How much power (in watts) is produced as radiation at this wavelength (1W=1 J.s^1)?

How do I go about solving this problem? I'm not sure where to start.

Jiyoon_Hwang_2I
Posts: 101
Joined: Sat Sep 14, 2019 12:17 am

### Re: 1.3

I think you use the equation E = hc/λ. You would plug in Planck's constant, the speed of light, and the wavelength which would be 633 nm (633 * 10^-9 m). Then, you would get your answer in J/photon. Then, multiply this answer to (2.4 * 10^21 photons). Your answer would be in joules, but since they indicated one second you would divide this answer by 1 second to get an answer in watts.

Cynthia Rodas 4H
Posts: 51
Joined: Wed Sep 18, 2019 12:21 am

### Re: 1.3

Since the problem is asking you to find the amount of power produced in watts, you would use the equation:
$E = \frac{hc}{\lambda }$
This would help you find the energy per photon. So then, you plug in Planck's constant (6.62608 x 10-34 J.s), the speed of light (2.998 x 108 m/s) and the given wavelength converted into meters (633 x 10 -9 m).
After plugging in everything, you should get 3.14 x 10-19 J/photon. So then you would multiply that by 2.4 x 1021 photons to get 750 J. Since the question is asking for the result in watts, which is J/s, you would divide the answer by 1 second to get 750 J/s.