## Homework 1.3

$c=\lambda v$

Annie Ye
Posts: 106
Joined: Wed Sep 18, 2019 12:22 am

### Homework 1.3

In each second, a certain lamp produces 2.4 3 1021 photons with a wavelength of 633 nm. How much power (in watts) is pro- duced as radiation at this wavelength (1W 5 1 J?s21)?

Chris Tai 1B
Posts: 102
Joined: Sat Aug 24, 2019 12:16 am

### Re: Homework 1.3

Here's what you know: there are 2.4x10^21 photons, and the wavelength of each photon is 633 nm.
Convert wavelength to meters - 633x10^-9 m.
Find frequency using (wavelength, 633x10^-9)(frequency) = (speed of light, 3x10^8) to get frequency v = 4.739x10^14
You can find the energy per photon to be E = hv = (6.626x10^-34)(4.739x10^14) = 3.14028x10^-19 J
Hence, the energy of all the photons combined is (3.14028x10^-19)(2.4x10^21) = 753.6672 J/s.
We need to convert this to watts, but since watts is just J/s, the answer is 750 W.