Question

The number of photons of wavelength 400 nm emitted from 10W electric bulb for 10 sec is

• A. 2.01 X 10²³
• B. 2.01 X 10²⁰
• C. 10²⁰
• D. 2 X 10²²

Answer 1

The correct option is B

2.01 X 10²⁰

10 W

Means 10J per second

10 sec - 100J is emitted

$100=n\times \frac{6.625{10}^{-34}\times 3\times {10}^8}{400\times {10}^{-9}}$

$n=\frac{100}{4.96\times {10}^{-19}}=2.01\times {10}^{20}$