CBSE 2025, Set 1

Question

Which of the following electromagnetic waves has photons of largest momentum ? A). X-rays B). AM radio waves C). Microwaves D). TV waves

Edvaya · Accepted Answer

The correct answer is X-rays. The momentum of a photon is given by de Broglie's relation: $$p = \frac{h}{\lambda} = \frac{h
u}{c} = \frac{E}{c}$$ Since $p \propto \frac{1}{\lambda} \propto 
u$, **higher frequency (shorter wavelength) → greater momentum**. The electromagnetic spectrum in order of increasing frequency (decreasing wavelength): $$	ext{Radio} p_{	ext{TV}} > p_{	ext{Microwave}} > p_{	ext{AM radio}}}$$ > **NCERT tip:** This question tests understanding of $p = h/\lambda$. The same principle explains why X-rays and γ-rays are more penetrating and damaging to biological tissue.

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Physics > Modern Physics > Electromagnetic Waves

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