Homework Question 1B.9

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Victoria Zheng--2F
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Joined: Fri Aug 09, 2019 12:17 am

Homework Question 1B.9

Postby Victoria Zheng--2F » Fri Oct 11, 2019 10:35 am

Homework Question 1B.9: A lamp rated at 32W (1W=1J/s) emits violet light of wavelength 470nm. How many photons of violet light can the lamp generate in 2.0s? How many moles of photons are emitted in that time interval?
I don't know how to approach this problem. Should I start with calculating the energy of the light?

Jiyoon_Hwang_2I
Posts: 101
Joined: Sat Sep 14, 2019 12:17 am

Re: Homework Question 1B.9

Postby Jiyoon_Hwang_2I » Fri Oct 11, 2019 12:06 pm

First, I would do 32W * 2.0s to find the amount of energy, in Joules, that is emitted in 2.0s as stated in the first question. Then, use the equation E=hc/λ to determine the energy per photon. For h use Planck's constant (6.626*10^-34 Js), c use the speed of light (2.99792*10^8 m/s), and λ use wavelength of violet light that is given (420 nm or 420*10^-9 m). After calculating, you should get an answer in J/photon. Divide 64 J (from 32W * 2.0s) by the answer you just calculated to get the number of photons of violet light that the lamp can generate in 2.0s.

To find the moles of photons, use Avogadro's constant. So, take your answer from the previous question and multiply it by (1 mol/6.022*10^23 photons).

Brittany Tran 3I
Posts: 50
Joined: Sat Jul 20, 2019 12:16 am

Re: Homework Question 1B.9

Postby Brittany Tran 3I » Fri Oct 11, 2019 4:57 pm

You can find the energy emitted with 2.0 s * (32 J/s) = 64 J. Then, you can find energy per photon by using the equation E = hc/wavelength. Then just divide total energy emitted by energy per photon, and you'll get the number of photons of violet light that the lamp can generate in 2.0 seconds. To find moles of photons, divide the number of photons by Avogadro's number.


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