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Monochromatic light of frequency $6.0 \times 10^{14}$ Hz is produced by a laser. The power emitted is $2 \times 10^{-3}$ W. The number of photons emitted, on the average, by the source per second is
A
$5 \times 10^{16}$
B
$5 \times 10^{17}$
C
$5 \times 10^{14}$
D
$5 \times 10^{15}$
Detailed Solution
Energy of one photon: $E = h\nu$
If $n$ photons are emitted per second, the power is $P = nh\nu$
$\Rightarrow n = \dfrac{P}{h\nu}$
$n = \dfrac{2 \times 10^{-3}}{6.6 \times 10^{-34} \times 6 \times 10^{14}}$
$n = \dfrac{2 \times 10^{-3}}{3.96 \times 10^{-19}}$
$n \approx 5 \times 10^{15}$ photons per second
If $n$ photons are emitted per second, the power is $P = nh\nu$
$\Rightarrow n = \dfrac{P}{h\nu}$
$n = \dfrac{2 \times 10^{-3}}{6.6 \times 10^{-34} \times 6 \times 10^{14}}$
$n = \dfrac{2 \times 10^{-3}}{3.96 \times 10^{-19}}$
$n \approx 5 \times 10^{15}$ photons per second