## 1B.9 (7th edition)

$E=hv$

hannahdaijo_4H
Posts: 48
Joined: Fri Sep 28, 2018 12:27 am

### 1B.9 (7th edition)

The textbook says, "...the intensity of radiation is an indication of the number of photons present, whereas E = hv is a measure of the energy of each individual photon." But in 1B. 9 (of the 7th edition), the question asks for the number of photons that can be generated and how many moles of photons are emitted in the given time interval. What denotes intensity if E = hv indicates energy? Or are they the same in practice? And can someone please explain the steps for how to get the answer to the second part of the problem ?

juliefilice 4A
Posts: 31
Joined: Fri Sep 28, 2018 12:27 am

### Re: 1B.9 (7th edition)

Energy and intensity aren't the same in practice. You first find the total energy (32W*1J/s*2s=64J), then find the energy per photon using E=hc/lambda. Calculate the number of photons by dividing the total energy by the energy/photon, then convert this number to moles by dividing by Avogadro's number for part 2.

Posts: 46
Joined: Wed Sep 30, 2020 9:36 pm

### Re: 1B.9 (7th edition)

First, you calculate 2s•32J/s=64J (total energy). We are also given the wavelength (420nm) which we need to convert to meters in order to plug into the equation (c= λv) and solve for frequency. Once we have the frequency, we can solve for the energy of a photon by multiplying the frequency by Planck’s constant (E=hv). Since Total Energy/Energy of a photon=number of photons generated, you divide 64J by the energy you just found. Then you divide the number of photons by Avogadro’s number to find how many moles of photons are emitted in 2 seconds.

Tikva Cohen 2I
Posts: 47
Joined: Wed Sep 30, 2020 9:39 pm

### Re: 1B.9 (7th edition)

Where does the 32W come from in this problem?? I'm confused?

Isabel_Eslabon_2G
Posts: 45
Joined: Wed Sep 30, 2020 9:50 pm

### Re: 1B.9 (7th edition)

Tikva Cohen 2I wrote:Where does the 32W come from in this problem?? I'm confused?

The 32W is given in the problem:

1B.9 A lamp rated at 32W(1W=1J⋅s^−1) 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?

Tikva Cohen 2I
Posts: 47
Joined: Wed Sep 30, 2020 9:39 pm

### Re: 1B.9 (7th edition)

Isabel_Eslabon_2G wrote:
Tikva Cohen 2I wrote:Where does the 32W come from in this problem?? I'm confused?

The 32W is given in the problem:

1B.9 A lamp rated at 32W(1W=1J⋅s^−1) 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?

ohhh what okay then my textbook is messed up that makes so much more sense!!! Mine looks like this "1B.9 A lamp rated at 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?"

Does anyone know why/how it's missing things?

Isabel_Eslabon_2G
Posts: 45
Joined: Wed Sep 30, 2020 9:50 pm

### Re: 1B.9 (7th edition)

Tikva Cohen 2I wrote:
Isabel_Eslabon_2G wrote:
Tikva Cohen 2I wrote:Where does the 32W come from in this problem?? I'm confused?

The 32W is given in the problem:

1B.9 A lamp rated at 32W(1W=1J⋅s^−1) 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?

ohhh what okay then my textbook is messed up that makes so much more sense!!! Mine looks like this "1B.9 A lamp rated at 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?"

Does anyone know why/how it's missing things?

That's very odd. You are on the Sapling textbook right? Or are you on a separate PDF of the textbook? If you are on Sapling, maybe its glitching since the formatting for how they enter equations is a bit different than normal text.

Tikva Cohen 2I
Posts: 47
Joined: Wed Sep 30, 2020 9:39 pm

### Re: 1B.9 (7th edition)

Isabel_Eslabon_2G wrote:
Tikva Cohen 2I wrote:
Isabel_Eslabon_2G wrote:
The 32W is given in the problem:

1B.9 A lamp rated at 32W(1W=1J⋅s^−1) 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?

ohhh what okay then my textbook is messed up that makes so much more sense!!! Mine looks like this "1B.9 A lamp rated at 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?"

Does anyone know why/how it's missing things?

That's very odd. You are on the Sapling textbook right? Or are you on a separate PDF of the textbook? If you are on Sapling, maybe its glitching since the formatting for how they enter equations is a bit different than normal text.

Yeah I’m on sapling and it’s glitched like this before so I have no idea. Do you have a pdf version or something I can use instead?

Isabel_Eslabon_2G
Posts: 45
Joined: Wed Sep 30, 2020 9:50 pm

### Re: 1B.9 (7th edition)

Tikva Cohen 2I wrote:
Isabel_Eslabon_2G wrote:
Tikva Cohen 2I wrote:

ohhh what okay then my textbook is messed up that makes so much more sense!!! Mine looks like this "1B.9 A lamp rated at 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?"

Does anyone know why/how it's missing things?

That's very odd. You are on the Sapling textbook right? Or are you on a separate PDF of the textbook? If you are on Sapling, maybe its glitching since the formatting for how they enter equations is a bit different than normal text.

Yeah I’m on sapling and it’s glitched like this before so I have no idea. Do you have a pdf version or something I can use instead?

I only use Sapling but I think if you search through one of those textbook databases online you'd be able to find the textbook PDF.