Monochromatic light of frequency 6 × 10¹⁴ Hz is produced by a laser. The power emitted is 2 × 10⁻³ W. How many photons per second on an average, are emitted by the source? (Given h = 6.63 × 10⁻³⁴ Js) (a) 5 × 10¹⁵ (b) 7 × 10¹⁶ (c) 6 × 10¹⁵ (d) 9 × 10¹⁸

Answer: (a). E = hν = (6.63 × 10⁻³⁴)(6 × 10¹⁴) = 3.98 × 10⁻¹⁹ J n = P/E = 2 × 10⁻³3.98 × 10⁻¹⁹ ≈ 5 × 10¹⁵ s⁻¹ So the answer is (a) 5 × 10¹⁵.

Monochromatic light of frequency 6 × 10¹⁴ Hz is produced by a laser… | JEE Main 2024 (1 Feb, Shift 2)

Q13JEE Main 2024 · 1 FEB · SHIFT 2Easy

Photons: Energy, Momentum & Radiation Pressure

Monochromatic light of frequency $6 \times 10^{14}\text{ Hz}$ is produced by a laser. The power emitted is $2 \times 10^{-3}\text{ W}$ .

How many photons per second on an average, are emitted by the source?

(Given $h = 6.63 \times 10^{-34}\text{ Js}$ )

Show answer and solution

Answer: (a)

$E = h\nu = (6.63 \times 10^{-34})(6 \times 10^{14}) = 3.98 \times 10^{-19}\text{ J}$
$n = \frac{P}{E} = \frac{2 \times 10^{-3}}{3.98 \times 10^{-19}} \approx 5 \times 10^{15}\text{ s}^{-1}$
So the answer is (a) $5 \times 10^{15}$ .