Question

Q7

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7. A light source emits a beam of photons, each of which has a momentum of 1.30 x 10-29 kg.m/s. What is the frequency of the photons? Hz

Answer 1

A photon is a particle which carries light energy. It is the particle corresponding to the 'particle nature' of light. Due to its particle-like characteristics, it also carries momentum with itself.

The momentum of a photon depends on its wavelength (and hence on its frequency). In other words, for a given optical medium, the momentum of a photon is uniquely characterized by its frequency/wavelength.

The momentum of a photon depends on its wavelength, λλ, as:

p=h/λ

While the wavelength, λ, and frequency, f, are related to the speed of light, which is a constant for a given medium:

fλ=c ⇒λ=c/f

Therefore, the momentum of the photon can be expressed in terms of its frequency as:

p=h/λ = h*f/c

The frequency of the photon then becomes:

f=p*c/h => (1.3*10^-29 *3*10⁸)/(6.626×10^-34 ) = 5.88*10¹²Hz

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