calculation for the number of photons?! (1 Viewer)

[Gillywilly]

yeah.. so anyone remember what/how they got an answer for that question??
it kinda threw me off

THANKS

 

[Joshrerts]

i got something to the power of 18 i think.

i just found out the energy of one photon and then divided the needed energy by the energy i calculated and done!

 

[weirdguy99]

The answer is 2.26x10^15 photons. You find the photon energy from the given wavelength, then divide the total energy by photon energy.

I think the wavelength was 450nm and the given total energy was 1x10^-3 J.

 

[Fizzy_Cyst]

There u go James!

 

[Gillywilly]

The answer is 2.26x10^15 photons. You find the photon energy from the given wavelength, then divide the total energy by photon energy.

I think the wavelength was 450nm and the given total energy was 1x10^-3 J.

oh really?! i thught you had to multiply that answer by 1.602 x 10^-19 to get the number of photons.. SIGH!!
went a step too far..

 

[Wight]

I did something dodgy mid calculation...got some huge retarded number. Hopefully my method resembled something like that so I get at least 1-2 marks for it :S.

 

[weirdguy99]

oh really?! i thught you had to multiply that answer by 1.602 x 10^-19 to get the number of photons.. SIGH!!
went a step too far..

I think that would convert your photon energy from Joules to eV.

 

[packwolf]

Argh, How many marks can i get for forgetting to convert nm to meters?

 

[weirdguy99]

Argh, How many marks can i get for forgetting to convert nm to meters?

I guess you'll lose 1??

 

[SpreadTheWord]

That was a hard question

 

[Fizzy_Cyst]

I went through pretty much this EXACT question with my class, except it was a 1mW laser with wavelength 700nm.

Most of them remembered YAYYYY

 

[weirdguy99]

I went through pretty much this EXACT question with my class, except it was a 1mW laser with wavelength 700nm.

Most of them remembered YAYYYY

What would you have written for the question where they asked you to compare/contrast(?) the difference between the 1MW red and blue laser?

 

[smash93]

There u go James!

DAMN that second last step.. i had the reciprocal

 

[PaterzAttack]

never encountered this type of question before, it had me stumped

 

[Fizzy_Cyst]

What would you have written for the question where they asked you to compare/contrast(?) the difference between the 1MW red and blue laser?

We did this exact question too, haha. It's from a past paper.

It was contrast, so differences only.

I would talk about the differences in individual energies of the photons of red/blue light and then the fact that there must be more photons in the red light as the power is the same, but photons of red light have a lower energy.

 

[markrule5]

i wrote down the formula for finding energy rekcon i can get 1 mark?

 

[weirdguy99]

We did this exact question too, haha. It's from a past paper.

It was contrast, so differences only.

I would talk about the differences in individual energies of the photons of red/blue light and then the fact that there must be more photons in the red light as the power is the same, but photons of red light have a lower energy.

HELL YEAH! I talked about the the difference in energies and then how the red light must have a greater intensity relative to the blue light since they have the same power.

 

[utanobeiiby]

got this too! xD

 

[jamesfirst]

There u go James!

YES

got it right.

 

[SnowTau]

no way!

I had NO idea what I was doing. I decided to use E = hf and ended up with E = hc/lambda (obviously), and got a number. From there I was just like... uhh wat. I wasn't even sure what that number was telling me to be honest, kinda missed this stuff. Then, in the question there was an energy value greater than the one I had so I was like meh, lets divide and bam got that answer.