The number of photons of wavelength of 540 nm emitted per second by an electric bulb

The number of photons of wavelength of 540 nm emitted per second by an electric bulb of power 100 W is (given h=6×10⁻³⁴ J-s)

Options

(a) 100
(b) 1000
(c) 3×10²⁰
(d) 3×10¹⁸

Correct Answer:

3×10²⁰

Explanation:

Power = nhc / ( × t)

⇒ 100 = [n × (6 × 10⁻³⁴) × (3 × 10⁸)] / (540 × 10⁹ × 1)

⇒ n × 18 × 10⁻²⁶ / 540 × 10⁻⁹ = 100

⇒ n = 100 × 540 × 10⁻⁹ / 18 × 10⁻²⁶ = 3 x 10²⁰

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