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Dual Nature of Radiation and Matter — Physics STD 12 Science — Question

Bihar BoardEnglish MediumSTD 12 SciencePhysicsDual Nature of Radiation and Matter1 Mark
Question
For question two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions front the codes (a), (b), (c) and (d) as given below.
  1. Both A and R are true and R is the correct explanation of A.
  2. Both A and R are true but R is NOT the correct explanation of A.
  3. A is true but R is false.
  4. A is false and R is also false.
Assertion (A): A photon has no rest mass, yet it carries definite momentum.
Reason (R): Momentum of photon is due to its energy and hence its equivalent mass.
✓

Answer

  1. Both A and R are true and R is the correct explanation of A.

Explanation:

Equivalent mass of photon (m) is given from equation

$\text{E}=\text{mc}^2=\text{h}\upsilon\therefore\text{m}=\frac{\text{h}\upsilon}{\text{c}^2}$

where E is energy, m is mass, c is speed of light, h is Planck's constant, $\upsilon$ is frequency.

$\therefore$ Momentum of photon $=\frac{\text{h}\upsilon}{\text{c}^2}\times\text{c}=\frac{\text{h}\upsilon}{\text{c}}$

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