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Concepts Of Physics MCQ Edition [Volume 2]

Exam: Concepts Of Physics MCQ Edition [Volume 2]
Subject: Physics
Chapter: Photoelectric Effect and Wave–Particle Duality

Concepts Of Physics MCQ Edition [Volume 2] · Physics · Photoelectric Effect and Wave–Particle Duality

Compute the number of photons emitted per second by a 10 W sodium...

Compute the number of photons emitted per second by a

10 \text{ W}

sodium vapour lamp. Assume that

60\%

of the consumed energy is converted into light. The wavelength of sodium light is

590 \text{ nm}

.

Options

A $1.77 \times 10^{18}$
B $2.95 \times 10^{19}$
C $1.06 \times 10^{19}$
D $1.77 \times 10^{19}$

Correct answer

D. $1.77 \times 10^{19}$

Step-by-step solution

Power of the lamp,

P = 10 \text{ W}

Energy converted into light per second,

E_{\text{light}} = \dfrac{60}{100} \times 10 = 6 \text{ J/s}

Wavelength of sodium light,

\lambda = 590 \text{ nm} = 590 \times 10^{-9} \text{ m}

Energy of one photon is given by

E = \dfrac{hc}{\lambda}

E = \dfrac{6.63 \times 10^{-34} \times 3 \times 10^8}{590 \times 10^{-9}} \approx 3.37 \times 10^{-19} \text{ J}

Number of photons emitted per second,

n = \dfrac{E_{\text{light}}}{E}

n = \dfrac{6}{3.37 \times 10^{-19}} \approx 1.77 \times 10^{19}

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