JEE Main 2026 — Jan 28, Shift 2 — Physics solution

JEE Main2026Jan 28, Shift 2Physics

Number of photons of equal energy emitted per second by a 6 mW laser source operating at 663 nm is ____ . (Given $h = 6.63 \times 1 0^{- 34}$ J $\cdot$ s and $c = 3 \times 1 0^{8}$ m/s)

A
$5 \times 1 0^{16}$
B
$5 \times 1 0^{15}$
C
$10 \times 1 0^{15}$
D
$2 \times 1 0^{16}$

Solution

Power $P = n \cdot \frac{h c}{λ}$ , where $n$ is photons per second.

$6 \times 1 0^{- 3} = \frac{n \times 6.63 \times 1 0 ^{- 34} \times 3 \times 1 0 ^{8}}{663 \times 1 0 ^{- 9}}$ .

Numerically, $\frac{h c}{λ} = \frac{6.63 \times 3}{663} \times 1 0^{- 17} = 3 \times 1 0^{- 19}$ J.

$n = \frac{6 \times 1 0 ^{- 3}}{3 \times 1 0 ^{- 19}} = 2 \times 1 0^{16}$ photons/s.

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