Skip to main content
Physics Guru is an online education and competitive examinations preparation portal founded by Manish Verma, an IIT Madras alumnus, providing learning resources for competitive examinations.

The emphasis is on conceptual understanding, analytical thinking and problem solving rather than simply memorising formulas and standard methods.

The objective is to help students understand what they are learning and develop the ability to solve problems they have not seen before.

The number of photons per second on an average ....

The number of photons per second on an average emitted by the source of monochromatic light of wavelength 600 nm, when it delivers the power of $3.3 \times 10^{-3}$ watt will be: ($h=6.6\times 10^{-34}$Js)

(1) $10^{18}$
(2) $10^{17}$
(3) $10^{16}$
(4) $10^{15}$

Solution

Let there be n number of photons per second.

Total energy per second of n number of photons = $n. \frac {hc}{\lambda} = 3.3 \times 10^{-3}$

$\therefore n=\frac {3.3 \times 10^{-3} \times 600 \times 10^{-9}}{6.6 \times 10^{-34} \times 3 \times 10^8} =10^{16}$

Answer: (3)