Solution
The
average frequency of the visible light range given in the question is
550 nm
A
50 W lamp produces 50J of light energy in 1 second.
so
a 550 nm photon will have energy of
6.63
x 10-34 x 3.0 x 108
550
x 10 -9
=
3.62 x 10 -19 J
Therefore
50J of light energy will contain 50/ (3.62 x 10 -19) = 1.4
x 1020