A $20$ watt bulb emits monochromatic light of wavelength $500$ nm. The number of photons emitted per second by the bulb is

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Solution

Answer (4)
Power of bulb $= 20$ watt $= 20$ Js $^{- 1}$
Energy of one proton $= \frac{h c}{λ}$
$= \frac{6.6 \times 10^{- 34} \times 3 \times 10^{8}}{500 \times 10^{- 9}}$
$= 3.96 \times 10^{- 19}$ J
Number of photons emitted $= \frac{20 {Js}^{- 1}}{3.96 \times 10^{- 19}}$
$= 5.05 \times 10^{19}$ photons s $^{- 1}$

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A 20 watt bulb emits monochromatic light of wavelength 500 nm. The number of photons emitted per second by the bulb is

Answer (4) Power of bulb =20 watt =20 Js−1 Energy of one proton =hcλ =6.6×10−34×3×108500×10−9 =3.96×10−19 J Number of photons emitted =20 Js−13.96×10−19 =5.05×1019 photons s−1

A $20$ watt bulb emits monochromatic light of wavelength $500$ nm. The number of photons emitted per second by the bulb is