Question

The number of photons of wavelength 540 nm emitted per second by an electric bulb of power 100 w is

Answer 1

Solving, we get the answer as 750 x 10^15 .

Answer 2

Concept:

The number of photons emitted per second by an electric bulb (n/t) is given by using the concept of power and energy .

Given:

wavelength(λ) = 540 nm , power of electric bulb (P)=100W,planck constant(h)= 6×10⁻³⁴

Find:

we will find out the no. of photons emitted per second (n/t).

Solution:

As we know that,

                           P = work done/ time taken

                           P  = energy/ time taken ---------1

                And we also know that

                Energy = nhc÷ λ

     So putting the value of energy in equation 1

         P = nhc÷ λt

         P = n/t ×hc/λ

        ∴n/t = Pλ÷hc

                 = 100×540×10⁻⁹÷6×10⁻³⁴×3×10⁸

                 = 3 ×10²⁰

Hence the number of photons emitted per second by an electric bulb is 3×10²⁰.

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