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JEE Main 2026 · 8 Apr · Shift 2, Physics question 38

A monochromatic source of light operating at 15 kW emits 2.5×10222.5\times10^{22} photons/s. The region of an electromagnetic spectrum to which the emitted electromagnetic radiation belongs to ________.

(Take h=6.6×10−34h=6.6\times10^{-34} J.s and c=3×108c=3\times10^8 m/s).

Choose one option
Answer and worked solution

Official answer: D

Photon energy. E=150002.5×1022=6×10−19E=\dfrac{15000}{2.5\times10^{22}}=6\times10^{-19} J.

Wavelength.
λ=hcE=1.98×10−256×10−19=330 nm:\lambda=\frac{hc}E=\frac{1.98\times10^{-25}}{6\times10^{-19}}=330\text{ nm}:
ultraviolet.

(D)

Topics:Photoelectric effectElectromagnetic spectrum
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