Question

An AIR station is broadcasting the waves of wavelength $300$ metres. If the radiating power of the transmitter is $10kW$, then the number of photons radiated per second is:

• A. $1.5\times {10}^{29}$
• B. $1.5\times {10}^{31}$
• C. $1.5\times {10}^{33}$
• D. $1.5\times {10}^{35}$

Answer 1

The correct option is B $1.5\times {10}^{31}$

Energy emitted by the transmitter per sec,$E_t=10$kW

Energy of the wave, $E_w=hc/\lambda$

where $\lambda =300$m

Plugging the values gives $E_w=6.6\times {10}^{-28}$

No of photons emitted per sec, $n=E_t/E_w=10000/6.6\times {10}^{-28}=1.5\times {10}^{31}$