A Small Gas Laser of the Type Used in Classrooms $2.0$

Short Answer

A small gas laser of the type used in classrooms may radiate light at a power level of $2.0$ $\mathrm { mW }$ . If the wavelength of the laser light is $642 \mathrm {~nm}$ , how many photons does it emit per second? $\left( c = 3.0 \times 10 ^ { 8 } \mathrm {~m} / \mathrm { s } , h = 6.626 \times 10 ^ { - 34 } \mathrm {~J} \cdot \mathrm { s } \right)$