JEE Main 2026 Physics question
A monochromatic source of light operating at 15 kW emits 2.5×10²² photons/s. The region of an electromagnetic spectrum to which the emitted electromagnetic radiation belongs to . (Take h = 6.6×10⁻³⁴ J·s and c = 3×10⁸ m/s).
Answer: (D)
Solution
Energy per photon=15×10³/2.5×10²²=6×10⁻¹⁹ J. λ=hc/E=(6.6×10⁻³⁴)(3×10⁸)/(6×10⁻¹⁹)=3.3×10⁻⁷ m=330 nm, which is ultraviolet.