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JEE Main 2020 (3 Sep, Shift 2) · Photons: Energy, Momentum & Radiation Pressure

Photons: Energy, Momentum & Radiation Pressure question from JEE Main 2020 (3 Sep, Shift 2)

Q28JEE Main 2020 · 3 SEP · SHIFT 2Easy

Photons: Energy, Momentum & Radiation Pressure

Two sources of light emit X-rays of wavelength 1 nm and visible light of wavelength 500 nm, respectively. Both the sources emit light of the same power 200 W. The ratio of the number density of photons of X-rays to the number density of photons of the visible light of the given wavelengths is:

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Answer: (a)

For equal power, photons per second $n \propto \lambda$ ; both travel at $c$ , so number density is also $\propto \lambda$ .
$\frac{n_X}{n_V} = \frac{1\text{ nm}}{500\text{ nm}} = \frac{1}{500}$
So the answer is (a) $\frac{1}{500}$ .

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