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.
Last updated
Read the Dawn of Modern Physics notesFree MDCAT chapter notes with key terms739 questions · page 3 of 37
- A. 1/2 mvmax2=hf+Φ
- B. 1/2 mvmax2-hf = Φ
- C. 1/2 mvmax2=hf-Φ
- D. All of above are correct
Explanation: Einstein's photoelectric equation is hf = Φ + Kmax, so Kmax = 1/2 mvmax^2 = hf - Φ.
Correct answer: 1/2 mvmax2=hf-Φ- A. infinite
- B. zero
- C. very small
- D. 1.67 x 10^-27 kg
Explanation: A photon has zero invariant or rest mass, although it carries energy E = hf and momentum p = E/c.
Correct answer: zero43. Stopping potential for a metal surface in case of photoelectric emission depends on_____________?
- A. the threshold frequency for the metal surface
- B. the intensity of incident light
- C. the frequency of incident light and work function of the metal surface
- D. all of the above
Explanation: The stopping potential satisfies eVs = hf - Φ = h(f - f0), so it depends on the incident frequency and the metal's work function, or…
Correct answer: the frequency of incident light and work function of the metal surface- A. T.V waves
- B. Microwaves
- C. X-rays
- D. γ-rays
Explanation: Photon energy is E = hf, so radiation with the greatest frequency has the strongest, or most energetic, photons.
Correct answer: γ-rays- A. Mass is not conserved
- B. Energy is not conserved
- C. Momentum is not conserved
- D. The chargee is not conserved
Explanation: A single photon cannot produce an electron-positron pair in empty space because energy and momentum cannot both be conserved by the…
Correct answer: Momentum is not conserved- A. Net energy is conserved
- B. Net charge is conserved
- C. Net momentum is conserved
- D. All of the above
Explanation: In pair production, a high-energy photon becomes an electron and a positron near a heavy nucleus.
Correct answer: All of the above- A. waves
- B. particles
- C. photons
- D. it was not his discovery
Explanation: Einstein explained the photoelectric effect by treating light as discrete packets of energy called photons, with each photon carrying…
Correct answer: photons- A. Hertz
- B. Fresnel
- C. Einstein
- D. Plank
Explanation: Einstein explained the photoelectric effect by proposing that light consists of photons with energy E = hf, and that one photon transfers…
Correct answer: Einstein- A. Proton
- B. Electron
- C. Neutron
- D. Photon
Explanation: A photon has zero rest mass, although it carries energy and momentum and travels at the speed of light in vacuum.
Correct answer: Photon- A. Green
- B. White
- C. Blue
- D. Black
Explanation: If a black body emits all visible colours with suitable intensities, their additive combination is perceived as white light.
Correct answer: White- A. Dilates
- B. Contracts
- C. Constant
- D. Uniform
Explanation: Special relativity predicts time dilation: a clock moving relative to an observer is measured to run more slowly, so the time interval…
Correct answer: Dilates- A. E=mc²
- B. E=hf
- C. E=m²c
- D. E=mv²
Explanation: Einstein's mass-energy relation states that the energy equivalent of mass m is E = mc², where c is the speed of light in m/s.
Correct answer: E=mc²- A. Exude
- B. Reflect
- C. Absorb
- D. None of these
Explanation: A black body is an ideal absorber that absorbs all incident electromagnetic radiation, regardless of wavelength or direction.
Correct answer: Absorb- A. Potential energy
- B. Rest energy
- C. Chemical energy
- D. Nuclear energy
Explanation: Matter has rest energy because a body of mass m possesses energy E = mc² even when it is not moving.
Correct answer: Rest energy- A. Quantum theory
- B. General theory of relativity
- C. Special theory of relativity
- D. None of these
Explanation: The relation E = mc² follows from special relativity, which treats mass and energy as equivalent forms of the same physical quantity.
Correct answer: Special theory of relativity- A. G
- B. h
- C. M
- D. E
Explanation: The prefix mega represents 10^6 and its SI symbol is capital M. The likely mistake is choosing G, which is the symbol for giga and…
Correct answer: M- A. protons
- B. positrons
- C. electrons
- D. photons
Explanation: Thermions are electrons emitted from a heated metal surface when thermal energy gives them enough energy to overcome the surface potential…
Correct answer: electrons- A. 10-4 sec
- B. 10-5 sec
- C. 10-3 sec
- D. 10-8 sec
Explanation: A metastable state has an unusually long lifetime, typically about 10^-3 s, compared with an ordinary excited state of roughly 10^-8 s…
Correct answer: 10-3 sec- A. Metal stable state
- B. Normal state
- C. Inverted population
- D. All the above
Explanation: When more atoms occupy the upper energy level than the lower level, the condition is called population inversion, which is necessary for…
Correct answer: Inverted population- A. Stimulated
- B. Absorbed
- C. Cause X-ray emission
- D. Cause laser production
Explanation: In the normal energy state, most atoms are in the lower level, so an incident photon with the correct energy is absorbed to raise an atom…
Correct answer: Absorbed