## 1.27

$c=\lambda v$

Irma Ramos 2I
Posts: 51
Joined: Fri Sep 29, 2017 7:07 am

### 1.27

A lamp rated at 32W emits violet light of wavelength 420 nm. How many photons of violet light can the lamp generate in 2.0 s? How many moles of photons are emitted in that time interval?

Thanks!

Tim Foster 2A
Posts: 73
Joined: Fri Sep 29, 2017 7:07 am

### Re: 1.27

Hey Irma! A key step of this problem is to find the energy created by one photon from this source of radiation, which we can do by using the formula E=hv, h being planck's constant (6.626x10^-34)
and v being the frequency. In order to plug the frequency into the above equation we must use the formula c=(wavelength)x(frequency). Once we find the frequency of the light to be 7.13809...x10^14HZ we can find the energy provided by one photon of the radiation using our first equation, E=hv. Now we can start to worry about the lamp in it's entirety. We divide the total energy produced by the lamp in two seconds (64J) by the energy produced by a single photon at this frequency (4.729...x10^-19) and your answer should come out to 1.4x10^20 total photons in two seconds.
Part b asks us how many moles of photons are emitted in this time interval, and so we simply divide our total photons from part A by avogadros number.
Hope this helped! Feel free to reply with any questions.