## Homework Question 1B.9

ariaterango_1A
Posts: 57
Joined: Wed Sep 18, 2019 12:15 am

### Homework Question 1B.9

Hi could someone help me with the set up of 1B.9? "A lamp rated at 32W (1W=1J.s^-1) emits violet light of wavelength 420nm. How many photons of violet light can the lamp generate in 2.0s? How many moles of photons are emitted in that time interval?

Ananta3G
Posts: 62
Joined: Wed Sep 18, 2019 12:19 am

### Re: Homework Question 1B.9

Hello! So the way to approach this problem is as follows: You know that a 32 watt lamp can generate 32 J per second because 1 watt is equivalent to 1 joule/s. Thus, in 2 seconds, the lamp will emit 64 J of energy. Next, you need to find out how much energy is emitted per photon by using the wave length. To do so, you need to use E = hc/lambda. Once of you have done that, you should divide 64 J (the total amount of energy of the lamp) by the value you calculated for E to get the number of photons that was used for 64 J of energy. To get moles, just do dimensional analysis with Avogadro's Number. Hope this explanation helps!

Ziyan Wang 3J
Posts: 51
Joined: Wed Sep 18, 2019 12:22 am

### Re: Homework Question 1B.9

Energy per photon=h*c/lambda=6.63*10^-34*3.00*10^8/(420*10^-9)=4.74*10^-19
Total energy= 32*2=64
# of photons= Total energy/energy per photon=64/(4.74*10^-19)=1.35*10^20