Monochromatic light of frequency 6.0 x 10¹⁴ Hz is produced by a laser. The power emitted is 2 x 10^-3 W. The number of photons emitted, on the average, by the source per second is:

5 x 10¹⁵

5 x 10¹⁶

5 x 10¹⁷

5 x10⁴

Solution

5 x 10¹⁵

Photons are the packets of energy. Power emitted ,
P = 2 x 10^-3 W
Energy of photon,
E = hv
= 6.6 x 10^-34 x 6 x 10¹⁴ J
h being planck's constant.
Numer of photons emitted per second
n = P/E
= 2 x 10^-3 / 6.6 x 10^-34 x 6 x 10¹⁴
⁼5 x 10¹⁵