1.

A bulb of 40 W is producing a light of wavelength 620 nm with `80%` of efficiency , then the number of photons emitted by the bulb in 20 seconds are : (`1eV = 1.6 xx 10^(-19) J , hc = 12400 eV`)A. `2 xx 10^(18)`B. `10^(18)`C. `10^(21)`D. `2 xx 10^(21)`

Answer» Correct Answer - D


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