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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 photons