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 22 of 37
- A. Pair production
- B. Photo electric effect
- C. Davison-Germer experiment
- D. De- Broglie concept
- E. Compton's effect
Explanation: The experimental proof of the particle nature of light is: Photoelectric effect.
Correct answer: Photo electric effect- A. The kinetic energy of the most energetic electron ejected
- B. The potential energy of the most energetic electron ejected
- C. The photon energy
- D. The electric potential that cause electron current to vanish
Explanation: In the photoelectric effect experiment, the stopping potential refers to the electric potential that is applied between the anode and the…
Correct answer: The electric potential that cause electron current to vanish- A. This proves law of conservation of energy
- B. This proves law of conservation of momentum
- C. This proves law of conservation of charge
- D. This proves law of conservation of mass-energy
Explanation: The inverse process to pair production is called pair annihilation, in which a particle and its antiparticle collide and annihilate each…
Correct answer: This proves law of conservation of momentum- A. Gamma photon
- B. Visible light photon
- C. Infrared photon
- D. All photons move with the speed of light
Explanation: A vacuum refers to the space in which no matter is present. Therefore, any object moving inside such space faces no frictional forces and…
Correct answer: All photons move with the speed of light- A. Alpha-rays
- B. One y-ray photon
- C. Two y-ray photons
- D. X-rays
Explanation: In anhhilation of matter two gamma rays photon are produced.
Correct answer: Two y-ray photons- A. Length
- B. Time
- C. Mass
- D. Frequency
Explanation: The standard Compton wavelength is denoted by the Greek letter λ (Lambda) measured using the SI unit of length angstrom (metre).
Correct answer: Length- A. Stefan's constant
- B. Boltzmann constant
- C. Rydberg's constant
- D. Coulomb's constant
- E. Planck's constant
Explanation: The ratio of the molar gas constant to Avogadro's number is called the Boltzmann constant .
Correct answer: Boltzmann constant- A. Magnetic flux
- B. Threshold frequency
- C. Work function
- D. Electric flux
- E. Wave function
Explanation: The symbol Φ in the equation Φ = hv represents the work function, which is the minimum energy required to remove an electron from the…
Correct answer: Work function- A. K.Emax=p+eV
- B. K.Emax = -eV
- C. K.Emax = -hv
- D. K.Emax = hv - φ
- E. K.Emax = hv-eVo
Explanation: The equation K.Emax=−eV refers to the maximum kinetic energy (K.E) of electrons in the context of the photoelectric effect or electron…
Correct answer: K.Emax = -eV- A. 6.63×10⁻³⁴ Js
- B. 6.63×10³⁴ Js
- C. 6.63 x 10^-36 Js
- D. 6.63×10³⁴ Js⁻¹
Explanation: . 6.63×10−34js ✅ - Correct, as this is the well-known value of Planck's constant, used in quantum mechanics to relate energy and frequency
Correct answer: 6.63×10⁻³⁴ Js431. The de-Broglie wavelength associated with a particle moving at 10⁶ m/s and having mass 10⁻³⁰ kg:
- A. 6.6 x 10^-10 m
- B. 1.5×10⁶ m
- C. 1.9×10⁻⁵ m
- D. 7.2×10⁻⁸ m
Explanation: Step 1: Calculate the momentum (p)p=mv=10-24kgm/sStep 2: Calculate the de Broglie wavelengthNow, substitute p into the de Broglie…
Correct answer: 6.6 x 10^-10 m- A. Interference
- B. Photoelectric effect
- C. Diffraction
- D. Polarization
Explanation: The photoelectric effect is a phenomenon in physics where electrons are emitted from a material (usually a metal) when it absorbs light or…
Correct answer: Photoelectric effect- A. 0°
- B. 45°
- C. 90°
- D. 180°
Explanation: The maximum value of Compton's shift occurs when the scattered photons are at an angle of 180 degrees with respect to the incident…
Correct answer: 180°434. The kinetic energy of emitted electrons in photoelectric effect can be increased by increasing _
- A. applied potential of electrodes
- B. frequency of electromagnetic wave
- C. intensity of incident light
- D. momentum of incident photon
Explanation: The kinetic energy of emitted electrons in the photoelectric effect can be increased by increasing the frequency of the electromagnetic…
Correct answer: frequency of electromagnetic wave- A. Angular spin of electron
- B. Energy of electron
- C. Energy of photon
- D. Scattering angle of photon
Explanation: The scattering angle of the photon is the most significant factor for calculating Compton's shift.
Correct answer: Scattering angle of photon- A. mc2
- B. I/h
- C. h/λ
- D. zero
Explanation: p=hf/cfrom this equation momentum becomes h/λ
Correct answer: h/λ- A. Below the threshold frequency
- B. Equals the threshold frequency
- C. Three times the threshold frequency
- D. Twice the threshold frequency
Explanation: The photoelectric effect does not occur if the frequency of the incident light is below the threshold frequency of the material.
Correct answer: Below the threshold frequency- A. Inconsistently
- B. Distinctly
- C. Equally
- D. Unequally
Explanation: While a black body emits radiation across all wavelengths, the distribution of that radiation is not equal in intensity; it follows a…
Correct answer: Equally- A. Intensity of incident light
- B. Color of the body
- C. Frequency of incident light
- D. Shape of the body
Explanation: The frequency of light is directly related to the energy of photons, which determines if photoelectrons will be emitted.
Correct answer: Frequency of incident light- A. √(e²/m)
- B. eV/m
- C. eV²/m
- D. √(2eV/m)
Explanation: Work Done by the Electric Field: The work done (W) by the electric field on the electron is equal to the charge of the electron (e)…
Correct answer: √(2eV/m)