Question

How many photons are emitted per second by a yellow lamp of power 10 watt? (Wavelength of yellow light = 600 nm)​

Answer 1

Answer:

Power= 10 W

Now, we know that Power= Energy/ time

Here time is given as 1 s.

Therefore energy (E) = 10 J

For a photon, we use the common relations-

E= nhc/ λ (OR) E = nhν

where h= Planck's constant =  6.6 × 10⁻³⁴J/s, c= speed of light=  3 × 10⁸, λ= wavelength of light, ν= frequency, n= number of photons

So now, 10 = n × 6.6 × 10⁻³⁴ × 3 × 10⁸/ 600 × 10⁻⁹  

         ⇒  n= 3 × 10¹⁹photons