Question

A discharge lamp produces 10 J of energy per
second in the blue region of the spectrum. How
many photons of blue (4700 A) light would the
lamp generate if it were left on for 17s ?​

Answer 1

Given :

Power of lamp = 10 J/s

Wavelength of photons = 4700 * 10^(-10) m

To find :

Numbers of photons generated in 17 seconds .

Solution :

Energy , E = ( n *  h * c )  / λ

where , h is Planck's constant ,

c is speed of light ,

λ is wavelength ,

and n is number of photons .

now ,

10 * 17 = ( n * 6.6 * 10^(-34) * 3 * 10^8 ) / 4700 * 10^(-10)

=> 170 = n * 0.421 * 10^(-18)

=> n = 4.03 * 10 ^ 20

The numbers of photons generated in 17 seconds are 4.03 * 10 ^ 20 approximately .