# Answer to Question #3423 in Quantum Mechanics for o m p

Question #3423

A laser delivers pulses of 2mJ at wavelength 633 nm with a pulse duration of 200 ps. <br>(hint E=h.c/l, with h=6.6 x10-34 J.s and c=3x108 m/s and 1 eV=1.6 x10-19 J) <br>i) How far do they travel in 1s? <br>ii) What is the photon energy in eV?<br>iii) How many photons are delivered per pulse?<br><br>& please show working out

Expert's answer

i) S=c*t=3*10

ii) eV=1.6*10

iii) energy of 1 photon is E

Thus

n = E/E

^{8}*1=3*10^{8}meters.ii) eV=1.6*10

^{-19}J → J=10^{19}/1.6 eV= 0.625*10^{19}eV=625*10^{16}eV → E=2*10^{-3}*10^{16}=2*10^{13}eViii) energy of 1 photon is E

_{1}= hc/λ=6.6*10^{-34}*3*10^{8}/633*10^{-9 }= 31.2*10^{-20}JThus

n = E/E

_{1}= 2*10^{-3}/31.2*10^{-20}= 6.4*31.2*10^{15}particles.
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