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JEE Main 2026 (8 Apr, Shift 2) · Photons: Energy, Momentum & Radiation Pressure

Photons: Energy, Momentum & Radiation Pressure question from JEE Main 2026 (8 Apr, Shift 2)

Q4JEE Main 2026 · 8 APR · SHIFT 2Medium

Photons: Energy, Momentum & Radiation Pressure

A monochromatic source of light operating at 15 kW emits 2.5×10222.5 \times 10^{22} photons /s/\text{s}. The region of an electromagnetic spectrum to which the emitted electromagnetic radiation belongs to ______. (Take h=6.6×10−34 J.sh = 6.6 \times 10^{-34}\text{ J.s} and c=3×108 m/sc = 3 \times 10^{8}\text{ m/s} ).

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Answer: (d)

  1. Energy per photon E=Pn=15×1032.5×1022=6×10−19 JE = \dfrac{P}{n} = \dfrac{15\times10^{3}}{2.5\times10^{22}} = 6\times10^{-19}\text{ J}
  2. λ=hcE=6.6×10−34×3×1086×10−19=3.3×10−7 m=330 nm\lambda = \dfrac{hc}{E} = \dfrac{6.6\times10^{-34}\times3\times10^{8}}{6\times10^{-19}} = 3.3\times10^{-7}\text{ m} = 330\text{ nm}
  3. 330 nm330\text{ nm} is shorter than violet (≈400 nm\approx 400\text{ nm}), so it is ultraviolet.
  4. So the answer is (d) Ultraviolet.
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