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 9 of 37
- A. K.E of all the emitted electrons
- B. Mean K.E of emitted electrons
- C. Maximum K.E of emitted electron
- D. Minimum K.E of emitted electrons
Explanation: The photoelectric equation K = hf - Φ is used to calculate the maximum kinetic energy of the emitted electron during the photoelectric…
Correct answer: Maximum K.E of emitted electron- A. 1.02 keV
- B. 1.02 MeV
- C. 1.02 eV
- D. 1.02 GeV
Explanation: Pair production occurs when the energy of the photon is at least 1.02 MeV.
Correct answer: 1.02 MeV- A. Mass is not conserved
- B. Energy is not conserved
- C. Momentum is not conserved
- D. Charge is not conserved
Explanation: Correct answer: C) Momentum is not conserved. The principle of conservation of momentum states that the total momentum of an isolated…
Correct answer: Momentum is not conserved- A. Electron
- B. β-particle
- C. Proton
- D. All
Explanation: To summarize, a positron (β+) has a charge in magnitude equal to the charge on an electron (e-), a β-particle (which can be an electron or…
Correct answer: All- A. Momentum
- B. Frequency
- C. Mass
- D. All of these
Explanation: In quantum physics, wave-particle duality states that any particle or quantum phenomenon can be represented as either a particle or a…
Correct answer: Mass- A. Momentum of photon is given by h/λ
- B. Rest mass of photon is zero
- C. Photon exert no pressure
- D. Energy of photon is hν
Explanation: The correct answer is that photons exert no pressure, which is incorrect.
Correct answer: Photon exert no pressure- A. Mass
- B. Energy
- C. Intensity
- D. None of these
Explanation: The intensity of light is directly related to the number of photons. When two photons move in the same direction, the intensity will…
Correct answer: Intensity- A. Appears as photon
- B. Appears as an electron- positron pair
- C. Appears as its K.E.
- D. It vanishes
Explanation: When a fast-moving electron loses energy, it can emit a photon. This phenomenon is known as bremsstrahlung radiation or braking…
Correct answer: Appears as photon- A. high-energy proton
- B. High-energy electrons
- C. High-energy -rays
- D. High-energy photons
Explanation: X-rays are a form of electromagnetic radiation similar to visible light.
Correct answer: High-energy photons- A. Electron
- B. Proton
- C. Neutron
- D. Alpha particle
Explanation: The wavelength of a particle is inversely proportional to its momentum. Momentum is given by the product of mass and velocity.
Correct answer: Alpha particle- A. Visible light
- B. X-rays
- C. Ultraviolet light
- D. γ-rays
Explanation: Gamma rays have the highest energy because they are at the extreme end of the electromagnetic spectrum, characterized by very short…
Correct answer: γ-rays- A. P= mc
- B. P=mc^2
- C. P= Ec
- D. P= m^2c
Explanation: the momentum of a photon is given by a different equation. The momentum of a photon is given by the equation p = E/c, where p is the…
Correct answer: P= mc- A. The kinetic energy of all emitted electrons is hv0
- B. The kinetic energy of all emitted electrons is h (v-v0)
- C. The kinetic energy of the fastest electron is h (v-v0)
- D. The kinetic energy of all emitted electrons is hv
Explanation: The remaining energy hv-hv0 will be maximum kinetic energy that ejected electrons can have.View the attached image for further explanation.
Correct answer: The kinetic energy of the fastest electron is h (v-v0)- A. Zero
- B. Equal to the mass of electron
- C. Equal to the mass of proton
- D. Infinite
Explanation: Photons, being massless particles, have a rest mass of zero. According to special relativity, photons always travel at the speed of light…
Correct answer: Zero- A. 5.00 x 10^-25 Ns
- B. 5.00 x 10^-26 Ns
- C. 5.00 x 10^-43 Ns
- D. 5.00 x 10^-44Ns
Explanation: Using de broglie's wavelength mv=h/𝞴 Where h is planck's constant whose value is 6.6x10-³⁴J.s =6.6x10-³⁴/1.32x10-⁹ =5x10-²⁵ N.s Ans
Correct answer: 5.00 x 10^-25 Ns- A. E = hvc
- B. E = c/λ
- C. E = hv
- D. E =nλ/c
Explanation: The energy associated with a single photon is given by E = h ν , where E is the energy (SI units of J), h is Planck's constant (h = 6.626…
Correct answer: E = hv- A. 1.7 x 10^-15J
- B. 1.32 x 10^-19J
- C. 1.1 x 10^-27J
- D. 1.1 x 10^-48J
Explanation: The correct answer is 1.326x10^-19.Changes: making option B 1.326x10^-19 Explanation: As , E = hv E = hc / lamda E= (6.63X10^-34)…
Correct answer: 1.32 x 10^-19J178. A ball of mass 1g is moving with a velocity of 10³ m/s. The De_Broglie wavelength of the ball is:
- A. 13.26 × 10^-36 m
- B. 3.315 × 10-³⁴ m
- C. 6.63 × 10-³⁴ m
- D. 4.97 × 10^-26 m
Explanation: momentum= 1/1000 Kg×1000m/s λ= Ph = 1 6.6×10−34J/s /1=6.6×10 −34mOPTION (A,B and D) are incorrect.As, it is a numerical so it could have…
Correct answer: 6.63 × 10-³⁴ m- A. Photon
- B. Proton
- C. Meson
- D. Positron
Explanation: A single quantum of electromagnetic radiation is called a "photon." Photons are elementary particles that represent a discrete amount of…
Correct answer: Photon- A. 4*10^7 joules
- B. 4*10^{17}eV
- C. 6.6 *10^{-20} eV
- D. 4 *times 10 joules
Explanation: Using the uncertainty principle, we find \(\Delta E \geq 3.315 \times 10^{-30}\) J.
Correct answer: 6.6 *10^{-20} eV