Question

$A$ $25watt$ bulb emits monochromatic yellow light of wavelength of $0.57\mu m$. what will be the rate of emission of quanta per second?

• A. $7.17\times {10}^{10}$
• B. $7.17\times {10}^{19}$
• C. $71.7\times {10}^{19}$
• D. $71.7\times {10}^{-10}$

Answer 1

Answer: (B)

$7.17\times {10}^{19}$

Power of bulb, P = 25 Watt = 25 $J{s}^{–1}$

We know, Energy of one photon, $E=hc/\lambda$

Substituting the values in the given expression of E:

$E=\frac{6.626\times {10}^{-34}\times 3\times {10}^8}{0.57\times {10}^{-6}}$

$E=34.87\times {10}^{–20}J$

Rate of emission of quanta per second is given by R = P/ E, Where R is the rate of emission, P is the power & E is the energy

Substituting the values in the equation we get

$=\frac{25}{34.87\times {10}^{-20}}=7.17\times {10}^{19}{s}^{-1}$