Chapter 1 Question 27


Moderators: Chem_Mod, Chem_Admin

Keshav Bhatnagar 1H
Posts: 32
Joined: Fri Sep 28, 2018 12:17 am

Chapter 1 Question 27

Postby Keshav Bhatnagar 1H » Sun Oct 21, 2018 5:29 pm

Hi, I'm not sure how to do this problem and the solutions manual doesn't really help. Here is the problem:

A lamp rated at 32 W (1 W  1 Js1) 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?

katherinemurk 2B
Posts: 68
Joined: Wed Nov 15, 2017 3:02 am

Re: Chapter 1 Question 27

Postby katherinemurk 2B » Sun Oct 21, 2018 5:34 pm

First convert 420 nm to m. Then solve for the energy per photon by using the equation E=hc/(wavelength). Once you have that answer, you can divide the total energy which is 64J (1 W= 1 J.s, so 32 x 2=64 J) and divide that by the energy per photon. This will get you the amount in photons. To solve for moles of photons you basically just take the number of photons and divide by Avogadro's number. Sorry if this was confusing but I hope it helps.

305144105
Posts: 32
Joined: Thu May 10, 2018 3:00 am

Re: Chapter 1 Question 27

Postby 305144105 » Mon Oct 22, 2018 6:24 pm

1. Find the total energy that is emitted in the 2s time interval.
32W * 1Js^-1/W * 2s = 64J

2. Calculate the energy that is emitted per photon using the formula E = hc/λ. (Remember to convert 420nm to m.)
E = hc/λ = (6.626*10^-34) * (3*10^8) / (420*10-9) = 4.73*10-19 J / photon

3. Calculate how many photons, each emitting 4.73*10-19 J of energy, is needed to achieve the total energy of 64J.
64 / 4.73*10-19 = 1.35*10^20 photons

4. Convert the number of photons to moles.
1.35*10^20 * 1mol / 6.022*10^23 = 2.3*10^-4 mol of photons


Return to “Einstein Equation”

Who is online

Users browsing this forum: No registered users and 1 guest