Q149 / 155 · WBJEE 2025 · Physics

$10^{20}$ photons of wavelength 660 nm are emitted per second from a lamp. The wattage of the lamp is (Planck's constant $\left.=6.6 \times 10^{-34} \mathrm{Js}\right)$

  • Correct answer
    A
    30W
  • B
    60W
  • C
    100W
  • D
    500W

Solution

$P=N\left(\frac{h c}{\lambda}\right)$ $\mathrm{P}=10^{20} \times \frac{6.6 \times 10^{-34} \times 3 \times 10^8}{660 \times 10^{-9}}=30 \mathrm{~W}$

Hence, the correct answer is option: 'A'.

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