Question

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. $5\times 10^{15}$
• B. $5\times 10^{16}$
• C. $5\times 10^{17}$
• D. $5\times 10^{14}$

Answer 1

Answer: (A)

Photons are the packets of energy. Power emitted,
$P=2\times 10^{-3}W$
Energy of photon,
$E=hv$
$=6.6\times 10^{-34}\times 10^{14}J$
$h$ being Planck’s constant.
Number of photons emitted per second
$n=\frac{P}{E}$
$=\frac{2\times 10^{-3}}{6.6\times 10^{-34}\times 6\times 10^{14}}$
$=5\times 10^{15}$