 # Modern Physics MCQs

21. A photon is
A. A unit of energy
B. A positively charged particle
C. A quantum of electromagnetic radiation
D. A unit of wavelength

Answer: Option C

22. Which one of the following has the largest energy content?
A. 103 photons of wavelength 2 pm (γ-rays)
B. 102 photons of wavelength 1nm (x-rays)
C. 106 photons of wavelength 50?m (infrared)
D. 106 photons of wavelength 200nm (UV)

Answer: Option A

23. A transmitting station emits radio waves of wavelength λ at power P. If h is Planck’s constant & c the speed of light what is the rate of emission of photons?
A. λ
B. Speed of sound
C. Speed of light
D. h

Answer: Option C

24. After traveling through a vacuum a photon of light entering into some transparent denser medium. Thus the energy of light
A. Increases because wavelength decreases
B. Decreases because speed decreases
C. Remains same
D. Increases then decrease

Answer: Option C

25. In a photoelectric effect monochromatic light is incident on a metal surface. If the incident light of twice the intensity but of same wavelength the kinetic energy of the emitted electron
A. Becomes double
B. Remains same
C. Becomes half
D. First increases then decrease because of the curvilinear graph

Answer: Option B

26. If the wavelength of incident radiation is increased in photoemission then
A. The maximum kinetic energy of the photoelectrons increases
B. The minimum kinetic energy of the photoelectrons decreases
C. The minimum kinetic energy of the photoelectrons increases
D. The average kinetic energy of the photoelectrons decreases

Answer: Option D

27. If a photon is reflected from the mirror then the change in momentum of each photon is
A. Zero
B. Double
C. Half
D. 1

Answer: Option B

28. If n number of the photon is striking on a metal surface then total momentum exerted is
A. p
B. n
C. 0
D. None

Answer: Option A

29. A photon of wavelength 900nm behaves like a particle of mass
A. 5.53 x 10-36kg
B. 0 kg.
C. 2.46 x 10-36kg
D. 1.84 x 10-44kg

Answer: Option C

30. The velocity of a particle of mass m of de-Broglie wavelength λ is
A. v = 3 ×× 106 ms-1
B. v = 2 ×× 10 ms-1
C. v = 2 ×× 6 ms-1
D. v = 2 ×× 106 ms-1

Answer: Option D

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