Homework Problem 1B9

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Emma Scholes 1L
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Joined: Fri Sep 28, 2018 12:18 am

Homework Problem 1B9

Postby Emma Scholes 1L » Tue Oct 09, 2018 5:20 pm

A lamp rated at 32. W (1W=1J/s) emits violet light of wavelength 420nm. How many moles of photons are emitted in 2.0 seconds?

Mindy Kim 4C
Posts: 65
Joined: Fri Sep 28, 2018 12:25 am

Re: Homework Problem 1B9

Postby Mindy Kim 4C » Tue Oct 09, 2018 9:10 pm

First, you want to find the amount of Joules emitted in 2.0 seconds:
(32 J/s)(2.0 s) = 64 J

Next, you can find the energy of one photon with just the wavelength by using the equation E=hc/(wavelength):
E=((6.626x10^-34 Js)(3.0x10^8 m/s))/(4.20x10^-7 m)
E=4.733x10^-19 J

To find how many photons were emitted, you can divide the total number of Joules (energy) emitted in the 2.0 seconds (64 J) by the energy of each photon:
64 J/4.733x10^-19 J/photon = 1.4 x 10^20 photons

Finally, you convert this number to moles of photons by dividing by Avogadro's number:
(1.4x10^20 photons)/(6.022x10^23 photons/mol) = 2.3x10^-4 mol photons

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