Question

A laser used to weld detached retains emits light with a wavelength $652$ nm in pulses that are of $20ms$ duration. The average power during each pulse is $0.6W$. The energy in each pulse and in a single photon are :

• A. $7.5\times {10}^{15}eV,2.7eV$
• B. $6.5\times {10}^{16}eV,2.9eV$
• C. $6.5\times {10}^{16}eV,2.7eV$
• D. $7.5\times {10}^{16}eV,1.9eV$

Answer 1

The correct option is D $7.5\times {10}^{16}eV,1.9eV$

Energy of photon $=\frac{hc}{\lambda }$$=\frac{1240eV-nm}{652nm}(hc=1240eV-nm)$

$=1.9eV$

Energy $=$ Power $\times$ time

$=0.6\times 20\times {10}^{-3}\times \frac{1}{1.6\times {10}^{-16}}$

$=7.5\times {10}^{16}eV$