Question

A 100 watt bulb emits monochromatic light of wavelength 400 nm . Calculate the number of photons emitted per second by bulb

Answer 1

Hey dear,

● Answer -
N = 2×10^20 photons

● Explanation -
Energy of isolated photon is calculated by -
E = hc/λ
E = (6.63×10^-34 × 3×10^8) / (4×10^-7)
E = 4.97×10^-19 J

No of photons emitted per unit time is calculated by -
N = P / E
N = 100 / (4.97×10^-19 J)
N = 2×10^20 photons


Therefore, 2×10^20 photons are emitted.

Answer 2

Given that,

Power = 100 watt

Wavelength = 400 nm

We need to calculate the energy

Using formula of energy

$E=\dfrac{hc}{\lambda}$

Put the value into the formula

$E=\dfrac{6.63\times10^{-34}\times3\times10^{8}}{400\times10^{-9}}$

$E=4.97\times10^{-19}\ J$

We need to calculate the number of photons emitted per second by bulb

Using formula of power

$P=n\times E$

$n=\dfrac{P}{E}$

Put the value into the formula

$n=\dfrac{100}{4.97\times10^{-19}}$

$n=2.01\times10^{20}\ photons\ per\ sec$

Hence, The number of photons emitted per second by bulb is $2.01\times10^{20}$