photons (1 Viewer)

[clever angel]

hi again

another q'n

a beam of light falls onto a balck body and imaprts 0.10 mW of power onto it. wavelenght of light is 5 * 10^-7 m

calcualte frequency and the energy per photon of light. this is pretty easy
but i don't know how to do the next bit

calculate the number of photons per second striking the body ? is it just dividing energy by power

thankxxx

 

[香港!]

^
Frequency, f=1\T where T is the 'period' in seconds
Maybe you can use that

 

[jake2.0]

use the fact that power = energy/time, you already know the energy of one photon

 

[香港!]

hihi, I did it an alternative way instaed of using f=1\T
I got E=....
P=W\t=E\t
t=E\P
then i got t=3.9756 x 10^-24

but this answer was different to my T in the other way???
Maybe the f=1\T way is inappropriate?
or I made a mistake????

 

[jake2.0]

but it isnt asking you to find T

 

[香港!]

^
yeah, we found f
so i use f=1\T, T=1\f
but it turned out to be wrong...
so what's happening???

 

[jake2.0]

just divide power by the energy of each photon

 

[香港!]

^ yes i did dat
but i'm also interested to see why T=1\f answer is different hehehe

 

[jake2.0]

p = 0.1x10^6.

its mW not MW so p = 0.1x10^-3.

 

[Antwan23q]

i dont get it, are u tryin to find the time?

the question says to find the amount of photons on it per second

 

[jake2.0]

^ yes i did dat
but i'm also interested to see why T=1\f answer is different hehehe

i don't really know, maybe because T and t are not the same

 

[Captain Gh3y]

E = hc/L, find E.

p = nE/t, where n = number of photons

Let t = 1, divide both sides by E

n/1 = some number

Is that right now?

 

[KFunk]

Is that right now?

Sounds good to me. I'd just get f using f = c/wavelength.

Then E(per photon) = hf = energy/photon

P/hf = (Energy/Second) x (Photon/energy) = Photons per second

 

[香港!]

^ ahhh
Chain Rule!!

 

[KFunk]

^ ahhh
Chain Rule!!

Haha, I think you're on 4U withdrawal.