Question

If a 60 W light source is emitting 622 nm light, how long will it take for it to emit 100. mole of photons?

Answer 1

Find energy of 1 photon first

use:
E = h*c/lambda
=(6.626*10^-34 J.s)*(3.0*10^8 m/s)/(6.22*10^-7 m)
= 3.196*10^-19 J
This is energy of 1 photon

Energy of 1 mol = energy of 1 photon * Avogadro's number
= 3.196*10^-19*6.022*10^23 J/mol
= 1.925*10^5 J/mol
= 1.925*10^2 KJ/mol
Find energy of 1 mol of photon
Energy of n mol = n * energy of one mol
Energy of 100 mol = 100* 1.925*10^2 KJ
Energy of 100 mol = 1.925*10^4 KJ
Energy of 100 mol = 1.925*10^7 J

Now use:
E = Power * time
1.925*10^7 J = 60 W * time
time = 320833 s
time = 320833/3600 hr
time = 89 hr
Answer: 89 hours