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 6 of 37
- A. X-rays
- B. Beta rays
- C. Gamma rays
- D. No radiation need medium to travel
Explanation: Option A: X-rays are a form of electromagnetic radiation. Unlike beta particles, X-rays do not require a medium to travel.
Correct answer: Beta rays- A. 10 micrometer
- B. 100 micrometer
- C. 1 micrometer
- D. 2 micrometer
Explanation: A photon's speed is 3x108 m/s (as it is the fundamental particle of light, and this is lights speed) and since velocity of a wave is equal…
Correct answer: 1 micrometer- A. 10 micrometer
- B. 100 micrometer
- C. 1 micrometer
- D. 2 micrometer
Explanation: According to the formula of wavelength λ = c / fwhere c is the speed of light in a vacuum (approximately 3 x 108 meters per second).Plug…
Correct answer: 1 micrometer- A. 4 : 1
- B. 1 : 2
- C. 2 : 1
- D. 1 : 4
Explanation: Since a photon's momentum comes straight from its energy (p = E/c), doubling the energy automatically doubles the momentum.
Correct answer: 2 : 1- A. λ1>λ2
- B. λ1=λ2
- C. λ2>λ1
- D. λ1≥λ2
Explanation: If the second light has a higher frequency than the first, then the first must have the longer wavelength.
Correct answer: λ1>λ2- A. The photoelectric effect
- B. The Compton effect
- C. The relationship between momentum and energy for an electron
- D. The diffraction of electrons by crystals
Explanation: By Davison-Germer the diffraction pattern (diffraction of electrons by crystals) have been observed with electron, protons, neutron…
Correct answer: The diffraction of electrons by crystals- A. Infinite
- B. Zero
- C. Equal to proton
- D. None of the above
Explanation: Photons are massless particles. The rest mass of a photon is zero. Unlike particles with mass, such as electrons or protons, photons do…
Correct answer: Zero108. A photon is a:
- A. Unit of energy
- B. Quantum of electromagnetic radiations
- C. Positively charged particle
- D. Unit of wavelength
Explanation: Potons are the bundles of energy are integral part of electromagnetic radiations and they could not be sub divided.
Correct answer: Quantum of electromagnetic radiations- A. Becomes double
- B. Becomes half
- C. remains same
- D. First increase then decrease
Explanation: The maximum energy of photoelectrons depends on the nature of metal surface and the frequency of incident light.
Correct answer: remains same- A. Sodium-Potassium
- B. Helium-Neon
- C. Carbon-oxygen
- D. Magnesium-Sodium
Explanation: Sodium or potassium cathode emits electrons for visible light. Cesium coated oxidized silver emits electrons for infrared light and some…
Correct answer: Sodium-Potassium- A. Compton Effect
- B. Annihilation
- C. Pair-production
- D. X-rays production
Explanation: In photoelectric effect the electrons are emitted from the metal surface when it is exposed to light, while in production of X-rays when…
Correct answer: X-rays production- A. Same
- B. Different
- C. Both A & B
- D. Independent of frequency of incident light
Explanation: The stopping potential, in the context of the photoelectric effect, refers to the minimum potential difference (voltage) required to…
Correct answer: Independent of frequency of incident light- A. Intensity of incident light
- B. Wavelength of incident light
- C. Energy of incident light
- D. Frequency of incident light
Explanation: In photoelectric effect electrons are emitted instantaneously; the intensity of light detemines only their numbers.
Correct answer: Intensity of incident light114. Which physical quantity will change if intensity of light falling on metal's surface is increased?
- A. K.E of photo electrons
- B. Plate potential
- C. Velocity of photo electron
- D. Current
Explanation: By increasing intensity of light, numbers of emitted electrons are increased. Hence current will be increased.
Correct answer: Current- A. Threshold frequency
- B. Work function
- C. Cut-off frequency
- D. Threshold energy
Explanation: The minimum amount of energy required to escape the electron from the metal surface is called work function "Φ".
Correct answer: Work function- A. Infinite rest mass
- B. No rest mass and no charge
- C. Rest mass but no change
- D. A. and B. are correct
Explanation: Photons are the bundles of energy are integral part of electromagnetic radiations and they could not be sub divided.
Correct answer: No rest mass and no charge- A. Option A
- B. Option B
- C. Option C
- D. Option D
Explanation: Explanation is given below in the attached image.
Correct answer: Option C- A. Frequency
- B. Brightness
- C. Intensity
- D. Power
Explanation: In photoelectric effect the electrons are emitted with different energies.
Correct answer: Frequency- A. Wave nature
- B. Both wave and particle nature
- C. Particle nature
- D. All of these
Explanation: The phenomenon of photoelectric effect cannot be explained if we assume that light consists of waves and energy is uniformly distributed…
Correct answer: Particle nature- A. Voe2
- B. Vo2e
- C. Voe
- D. work function
Explanation: The maximum energy of photoelectrons is:
Correct answer: Voe