Question

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

Answer 1

Given - Energy produced by lamp - 10 J/s

Wavelength of blue light - 4700 Å = 4.7*10^-7 m.

Find - Photons of blue light generated by lamp in 17s.

Solution - Number of photons can be calculated by the formula - E = (n*h*c)/lambda.

In the formula, E is energy, n is number of photons, h is Planck's constant, c is speed of light and lambda is wavelength.

Speed of light - 3*10^8 m/s.

Planck's constant - 6.6*10^-34

Keeping the values in equation-

10*17 = n*6.6*10^-34*3*10^8/4.7*10^-7

n = 170*4.7*10^-7/(1.98*10^-25)

n = 7.99*10^-5/1.98*10^-25

n = 4.03*10^-30.

Hence, number of photons that will be released is 4.03*10^-30.