tricky q'n (1 Viewer)

[clever angel]

hi

if a 2W laser beam is emitting light of the wavelenght 600nm. the number of photons emitted per minute is closest to:
a) 6*10^12
b)6*10^18
c)6*10^36
d)6*10^43

sry, i don;t have the right answer

ne ideas, plzz show the working

 

[Ghost1788]

What answer did u get i didnt get any of those answers either...
heres my working if anyone wants to see and tell me what i've done wrong...if i have done something wrong

P=VI
E=VIT
E=hf
c=fλ

OK since
f=c/λ
=(3*10⁸)/(600*10^-9
=5*10¹⁴

Energy of one photon = hf
=6.626*10^-34 * 5*10¹⁴
=3.313*10^-19 J

But for 2W = 2 J per second , one minute equates to 2 J for 60 s
=2*60
=120 J over 1 minute

therefore number of photons = 120/(3.313*10^-19)
=3.622094778*10²⁰
=3.6 * 10²⁰ (1 dp)

 

[kynanld]

I followed your steps perfectly up untill the last one. Why is it that the number of photons per min is given by joules per min / energy of single photon? can you plz explain that in apples and oranges terms lol.

Aside from that i have seen questions simmilar note that it says the answer is closest to... therefore it would be answer b) even though it seems outrageous. I have done many questions with answers like this in SucessOne phyisics.

 

[helper]

In terms of Oranges, the amount of energy in the second last term, would represent the amount of orange juice produced.

Each orange produces the same amount of energy as a photon.

So to determine how many oranges we need, we divide how much orange juice we produce by the amount a single orange produces.

 

[kynanld]

Ohh right I get it now. Thx alot for explaining that like you did. Its much appreciated.

 

[great_guns]

yeah

im thirsty now...