Free Dawn of Modern Physics MCQs with Answers
739 Dawn of Modern Physics MCQs from Physics, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.
Classical physics cannot explain blackbody radiation and related observations, leading to Planck’s quantum theory, in which energy is emitted or absorbed in discrete packets. Photons provide the particle model of light, with energy and momentum linked to frequency and wavelength, including the photoelectric effect and its threshold frequency.
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Read the Dawn of Modern Physics notesFree MDCAT chapter notes with key terms739 questions · page 11 of 37
- A. Pair production
- B. Compton effect
- C. Photoelectric effect
- D. A & B are correct
Explanation: Option A: Pair production is a process in which a photon interacts with a nucleus or an electron and produces an electron-positron pair.
Correct answer: Photoelectric effect- A. The threshold frequency for the metal surface
- B. The intensity of incident light
- C. The frequency of incident light and the work function for metal surface
- D. The threshold energy for the metal surface
Explanation: The current is same but stopping potential is different for each frequency of incident lightThis fact shows that maximum K.E.
Correct answer: The frequency of incident light and the work function for metal surface- A. 1/2 MV2max = hf +Φ
- B. 1/2 MV2max = hf - Φ
- C. 1/2 MV2max - hf = Φ
- D. 1/2 MV2max - Φ = hf
Explanation: Energy of photon = work function + Max. K.E. of photoelectron
Correct answer: 1/2 MV2max = hf - Φ- A. Red
- B. Yellow
- C. Blue
- D. radio wave
Explanation: As wavelength of radio wave is greatest than others. So. its photon has least momentum.
Correct answer: radio wave- A. Photoelectric emission does not occur below the threshold frequency
- B. The photoelectric current increases with the frequency of incident light
- C. Threshold frequency depends on the metal used
- D. The emission of photoelectrons is an instantaneous process
Explanation: In photoelectric effect Electrons are emitted instantaneously; the intensity of light determines only their numbers.
Correct answer: The photoelectric current increases with the frequency of incident light- A. electron diffraction experiment of Davisson and Germer
- B. Thompson's measurement of e/m
- C. Young's double slit experiment
- D. the Compton effect
Explanation: Evidence for the wave nature of matter is electron diffraction experiments of Davisson and Germer.
Correct answer: electron diffraction experiment of Davisson and Germer- A. Intense beam of light
- B. Monochromatic beam of light
- C. Coherent beam of light
- D. All of the above
Explanation: A laser device can produce an intense, coherent, and monochromatic beam of light, making option (d) "All of the above" the correct…
Correct answer: All of the above- A. Very slow speed
- B. Very high speed
- C. Very high speed along a circular path
- D. None of these
Explanation: This is based on the concept of time dilation from Einstein's theory of relativity.
Correct answer: Very high speed along a circular path- A. Work
- B. Work function
- C. Power
- D. Wavelength
Explanation: The energy required to remove an electron from the surface of a metal is known as the work function.
Correct answer: Work function- A. Carry 1⁄4th of their previous energy
- B. Are 1/16th as numerous as before
- C. Carry 1⁄4th as their previous energy
- D. Carry 1/4th as their previous momentum
Explanation: I2/I1= (r1/r2)2As r1= 0.25mAnd r2= 1m we have I2/I1=1/16This is correct based on the change in intensity.
Correct answer: Are 1/16th as numerous as before- A. No change occurs
- B. The emission of photoelectrons stops
- C. K.E of the photoelectrons decreases but the strength of the photoelectric current increases
- D. K.E of the photoelectrons decreases but the strength of the photoelectric current decreases
Explanation: This is a plausible scenario. If the new light has a smaller wavelength (higher energy) and smaller intensity, the kinetic energy of the…
Correct answer: K.E of the photoelectrons decreases but the strength of the photoelectric current decreases- A. OR Gate
- B. AND Gate
- C. NOT Gate
- D. NOR Gate
Explanation: The NAND gate is a digital logic gate that operates the AND gate followed by the NOT gate.
Correct answer: NOT Gate- A. Intensity of the incident light
- B. Frequency of the incident light
- C. Temperature of the photosensitive surface
- D. None
Explanation: Intensity of the incident light: While the intensity of light can affect the number of photoelectrons emitted, it does not affect the…
Correct answer: Frequency of the incident light- A. 2P
- B. 4P
- C. 8P
- D. 6P
- E. 16P
Explanation: The information provided in the image states that:The power radiated by a black body at temperature T₁ is P, and it radiates maximum…
Correct answer: 16P- A. velocity
- B. angular momentum
- C. energy
- D. momentum
Explanation: Electrons and photons both exhibit wave-particle duality as per quantum mechanics.For a wave of same wavelength λ, the frequency f of the…
Correct answer: momentum- A. Space
- B. Inertial frame of reference
- C. Speed of light
- D. Time
Explanation: According to the theory of relativity, specifically Einstein's theory of special relativity, the fourth dimension added to the three…
Correct answer: Time- A. Very slow speed
- B. Very high speed
- C. Very high speed along a circular path
- D. None of these
Explanation: Correct. According to the theory of relativity, time dilation occurs at high speeds, affecting the aging processIn summary, the correct…
Correct answer: Very high speed along a circular path- A. Compton shift
- B. Compton wavelength
- C. full wavelength
- D. None
Explanation: Correct. At θ = 90°, the Compton shift is equal to the full wavelength of the incident X-raysIn summary, the correct option is **c.
Correct answer: full wavelength- A. Carry ¼th their previous energy
- B. Are 1/16th as numerous as before
- C. Are 1/4th as numerous as before
- D. Carry 1/4th their previous momentum
Explanation: Correct. The kinetic energy (and therefore momentum) of photoelectrons is determined by the potential difference and is independent of the…
Correct answer: Carry 1/4th their previous momentum- A. No change occurs
- B. Emission of photoelectrons stops
- C. K.E of the photoelectrons decreases, but the strength of the photoelectric current increases
- D. K.E of the photoelectrons decreases, but the strength of the photoelectric current decreases
Explanation: Correct. Smaller wavelength light results in more energetic photoelectrons, but the intensity may decreaseIn summary, the correct option…
Correct answer: K.E of the photoelectrons decreases, but the strength of the photoelectric current increases