Question

No. of photons emitted by a bulb of 40 watt in 1 minute with 50% efficiency (wavelength 6200A°)​

Answer 1

Answer:

no of photons =

$37.5 \times {10}^{20}$

Explanation:

given-

power of bulb=40watt

time - 60 seconds

efficiency of bulb=50%

wavelength =6200Å

to find-

no of photons

solution-

Energy of light Emmitted by bulb= E= power ×time

E = 40 × 60

= 2400 Joules

energy of light emitted = 2400 Joules

but

efficiency of bulb is 50%

so

energy = 2400×50/100= 1200 Joules

Energy of one photon= hc / wavelength

hc= 12400eVÅ

and wavelength = 6200Å

therefore energy of one photon=12400/6200= 2eV

1 eV= 1.6 × 10^(-19) Joules

so

energy of one photon = 3.2× 10^(-19)

now

no of photons= energy of light emitted by bulb/ energy of

one photon

= 1200Joules/3.2×10^(-19)

no of photons= 37.5× 10^(20).