question_answer 25)

Estimating the following two numbers should be interesting. The first number will tell you why radio engineers do not need to worry much about photons ! The second number tells you why our eye can never 'count photons', even in barely detectable light. (a) The number of photons emitted per second by a Medium wave transmitter of 10 kW power, emitting radio waves of wavelength 500 m. (b) The number of photons entering the pupil of our eye per second corresponding to the minimum intensity of white light that we humans can perceive Take the area of the pupil to be about 0.4 cm2, and the average frequency of white light to be about 6 x 1014 Hz.  

Answer:

(a) Number of photons emitted per second, Now, Power of transmitter This number is a very-very large quantity. (b) Minimum intensity Area of pupil Average frequency v  Energy of each photon,  number of photons entering into pupil of the eye per second This is quite a small number, but still large enough to be counted. Comparison of cases (a) and (b) tells us that our eye can not count the number of photons individually.