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Dual Nature of Radiation and Matter · Question 20

JEE Main 2025 (Online) 4th April Morning ShiftMCQMedium📈 Topic in 10% papers+4−1
1

A small mirror of mass m is suspended by a massless thread of length l. Then the small angle through which the thread will be deflected when a short pulse of laser of energy E falls normal on the mirror (c = speed of light in vacuum and g = acceleration due to gravity)

  1. = Emc gl
  2. = E2mc gl
  3. = 3E4mc gl
  4. = 2Emc gl

Answer

(4) = 2Emc gl

Solution

Momentum of the light pulse: p = Ec

The mirror reflects the pulse back, so the momentum given to the mirror: p = Ec - (- Ec ) = 2Ec

Speed of the mirror just after the pulse: v = 2Emc

Energy conservation as it swings up: 12mv2 = mgl(1 - )

For small : 1 - 22 v2 = gl 2 v = gl

= v gl = 2Emc gl

Answer: (4)

JEE Main 2025 (Online) 4th April Morning Shift

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2

Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R In the light of the above statements, choose the correct answer from the options given below

  1. Both A and R are true and R is the correct explanation of A
  2. A is false but R is true
  3. Both A and R are true but R is NOT the correct explanation of A
  4. A is true but R is false
JEE Main 2025 (Online) 4th April Morning Shift
3

The work function of a metal is 3 eV. The color of the visible light that is required to cause emission of photoelectrons is

  1. Red
  2. Green
  3. Blue
  4. Yellow
JEE Main 2025 (Online) 3rd April Morning Shift
4

If and K are de Broglie wavelength and kinetic energy, respectively, of a particle with constant mass, the correct graphical representation for the particle will be :

  1. [figure]
  2. [figure]
  3. [figure]
  4. [figure]
JEE Main 2025 (Online) 29th January Morning Shift
5

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). In the light of the above statements, choose the most appropriate answer from the options 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 false but (R) is true
  4. (A) is true but (R) is false
JEE Main 2025 (Online) 29th January Morning Shift
6

A proton of mass 'mp' has same energy 'E' as that of a photon of wavelength ' '. If the proton is moving at non-relativistic speed, then ratio of its de Broglie wavelength to the wavelength of photon is

  1. 1c Emp
  2. 1c 2Emp
  3. 12c Emp
  4. 1c E2mp
JEE Main 2025 (Online) 28th January Morning Shift
7

Which of the following phenomena cannot be explained by wave theory of light?

  1. Refraction of light
  2. Reflection of light
  3. Diffraction of light
  4. Compton effect
JEE Main 2025 (Online) 28th January Evening Shift

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