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 :
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. `2xx10^(18)`
B. `10^(18)`
C. `10^(21)`
D. `2xx10^(21)`
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Correct Answer - D
Power`=(nhC)/(lambdaxxt) rArr 40xx80/100=(nxx6.62xx10^(-34)xx3xx10^(8))/(620xx10^(-9)xx20) rArr n=2xx10^(21)`
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