Chemistry/Physics Help

[mosin40]

Hi guys, 

I need  some help in a chemistry question. 

The question is: A laser pointer emits a light of 4.72*10^14 Hz, and the power of the laser is 1mW, how many moles of photons does it emit per minute?

 

I already know that Power= Energy/Time. And I already found out the energy produced by the laser pointer (3.129*10^-19 J), but now i'm stuck. I really need some help

[flibberdipper]

Now how in the fuck is this chemistry?

 

Then again, half of the shit I'm doing in chemistry right now... Isn't even chemistry.

[mosin40]

Now how in the fuck is this chemistry?

 

Then again, half of the shit I'm doing in chemistry right now... Isn't even chemistry.

It's a mix of chem and physics, soo.....

[CydiaDash]

I'm 13... sooo there's that

[SteveGrabowski]

The energy of an individual photon is E = hf, where h is Planck's constant and f is the frequency.

[Zeke]

The energy of an individual photon is E = hf, where h is Planck's constant and f is the frequency.

Divide that (the amount of photons, that is) by 6.02*10^23 and there's your answer.

[mosin40]

The energy of an individual photon is E = hf, where h is Planck's constant and f is the frequency.

i already did that part, since E= hf then, E= 6.63*10^-34 * 4.72*10^14, and that is 3.129*10^-19 J. 

[mosin40]

Oops, double post.... 

[C_Mike]

Hi guys, 

I need  some help in a chemistry question. 

The question is: A laser pointer emits a light of 4.72*10^14 Hz, and the power of the laser is 1mW, how many moles of photons does it emit per minute?

 

I already know that Power= Energy/Time. And I already found out the energy produced by the laser pointer (3.129*10^-19 J), but now i'm stuck. I really need some help

 

You can't use moles to define the number of photons.

 

Ignore me. 

[SteveGrabowski]

You can't use moles to define the number of photons.

 

Sure you can, just like you can express the number of photons in terms of 1s, hundreds, billions, googols, etc.

[SteveGrabowski]

i already did that part, since E= hf then, E= 6.63*10^-34 * 4.72*10^14, and that is 3.129*10^-19 J. 

 

1. Next you need to find how much energy is produced in a minute by the laser. Energy = Power * Time

2. Now divide this energy by the energy of each photon, and you have the number of photons emitted in a minute.

3. Divide that number by Avogadro's constant and you get the number of moles of photons emitted in a minute.

[werto165]

E= hf so E = 6.63*10-34*4.72*10^14 Hz = E (where E is a single photon energy) 

 

P = E /t 

1*10^-3 *60 = E * Total number of photons

 

total # photons = 1*10-3*60/ E = 1.98*10^17 / 6.023*10^23(avagadros constant) = 3.29*10^-7? I not 100 % sure 

[Zeke]

i already did that part, since E= hf then, E= 6.63*10^-34 * 4.72*10^14, and that is 3.129*10^-19 J. 

That's the energy of a single photon. The energy emitted by a 1 mW laser is (W=J/s), therefore 1 mW during 60s equals to 0.06 J/min output. 

 

0.06/3.129*10^-19 equals to 2.87*10^20 photons per minute. Divide that by the Avogadro number, and get ~0.000477 moles/minute.

 

(the energy of a photon is based on OP's calculations, I haven't checked that)

 

So I managed to bollocks up the math, the guy below me has the right answer

[C_Mike]

1*10^-3 * 60 Is energy of Laser per minute = 60*10^-3

Energy of one photon is hf = 6.62606957*10^-34 * 4.72*10^14 = 3.128 *10^-19

 

60*10^-3/3.128*10^-19 = 1.91*10^17 Photons per minute

 

1.91*10^-21/6.02*10^23 = 3.18*10-7

[Zeke]

1*10^6 * 60 Is energy of Laser per minute = 60*10^6

Energy of one photon is hf = 6.62606957*10^-34 * 4.72*10^14 = 3.128 *10^-19

 

60*10^6/3.128*10^-19 = 1.91*10^26 Photons per minute

 

1.91*10^26/6.02*10^23 = 317.16

Dude, milliwatts, not megawatts :3

[C_Mike]

Dude, milliwatts, not megawatts :3

 

Yep corrected. My brain isn't fully functioning clearly

[werto165]

That's the energy of a single photon. The energy emitted by a 1 mW laser is (W=J/s), therefore 1 mW during 60s equals to 0.06 J/min output. 

 

0.06/3.129*10^-19 equals to 2.87*10^20 photons per minute. Divide that by the Avogadro number, and get ~0.000477 moles/minute.

isn't 0.06/3.129*10^-19 = 1.91*10^17? 

[mosin40]

Thank you very much!

Thanks for the quick replies! I

[Zeke]

isn't 0.06/3.129*10^-19 = 1.91*10^17? 

Yep, it is. I've mispressed a key so it became 90.06 :c

 

Should've used WolframAlpha