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 23 of 37
- A. increase
- B. decrease
- C. remain the same
- D. sometimes increase sometimes decrease
Explanation: Decreasing potential reduces the electron's kinetic energy and momentum.By De Broglie's equation (λ = h/p), lower momentum implies a…
Correct answer: increase- A. Below a certain frequency
- B. Beyond a certain wavelength
- C. Above a certain frequency
- D. None of the given options
Explanation: The photon energy must exceed the work function for electron emission.This is the correct answer.
Correct answer: Above a certain frequency- A. Newton
- B. Galileo
- C. Both Newton and Galileo
- D. Neither Newton nor Galileo
Explanation: Since both Newton and Galileo adhered to classical mechanics, they both believed in absolute time.Therefore, this option is correct.
Correct answer: Both Newton and Galileo444. When placed in light which of the following can generate an output voltage across its electrodes?
- A. P-N diode
- B. Light emitting diode
- C. Photo diode
- D. All of these
Explanation: Correct. A photodiode converts light into voltage.
Correct answer: Photo diode- A. 7.5×10^12 Hz
- B. 6×10^3 Hz
- C. 3×10^3 Hz
- D. 1.5×10^13 Hz
Explanation: Correct. Here's the calculation:Relationship between momentum and wavelength:p = h/λ, where p is momentum, h is Planck's constant (6.626 ×…
Correct answer: 1.5×10^13 Hz- A. The electric potential that causes the electronic current to vanish
- B. The photon energy
- C. The kinetic energy of the most energetic electron ejected
- D. The energy required to remove an electron from the sample
Explanation: The electric potential that causes the electronic current to vanish - Correct: Stopping potential is the voltage needed to stop even the…
Correct answer: The electric potential that causes the electronic current to vanish- A. Special conductivity
- B. Special resistivity
- C. Special theory of relativity
- D. General theory of relativity
Explanation: Special theory of relativity - Correct: Einstein's special theory of relativity states that the speed of light is constant for all…
Correct answer: Special theory of relativity- A. Photoelectric current
- B. Pair production
- C. Annihilation of matter
- D. Compton effect
Explanation: When two anti-particles, particles having the same masses but different charges, collide they are said to annihilate and vanish by…
Correct answer: Annihilation of matter- A. Huygen
- B. Fraunhoffer
- C. Fresnel
- D. Coulomb
- E. Maxwell
Explanation: In 1864, Maxwell conjectured from his famous equations that light is a transverse electromagnetic wave.
Correct answer: Maxwell- A. Δλ=h/moC(1+ Cosθ)
- B. λ=h/moC(1 - Cos2θ)
- C. Δλ=h/moC(1 - Cosθ)
- D. Δλ=h/moC2(1 + Cosθ)
Explanation: Option C is correct. The derivation is given below:
Correct answer: Δλ=h/moC(1 - Cosθ)- A. Option A
- B. Option B
- C. Option C
- D. Option D
Explanation: t = t0/(1-v2/c2)½ Is the formula used in the equation. This is just a factual recall.
Correct answer: Option B- A. 0
- B. a
- C. hf/c
- D. mv
Explanation: Photons have their momentum found from de Broglie's equation P=h/lambda, and "lambda" can be found by dividing f(speed of light) by "f"…
Correct answer: hf/c- A. Blue
- B. White
- C. Purple
- D. None of these
Explanation: When light with a sufficiently high-frequency shine on a metal plate like aluminum, electrons are ejected from the plate.
Correct answer: None of these- A. Appears as photon
- B. Appears as electron -positron pair
- C. Appears as its K.E
- D. It vanishes
Explanation: When a fast-moving electron loses energy, it can emit photons. This process is known as bremsstrahlung radiation, where the electron…
Correct answer: Appears as photon- A. Electric field
- B. Magnetic field
- C. Both Options A and B are correct
- D. None of these options are correct
Explanation: X-rays do not interact significantly with electric or magnetic fields, so they cannot be deflected by either.
Correct answer: None of these options are correct- A. Remains the same
- B. Increases
- C. Decreases
- D. None of these options are correct
Explanation: In Compton scattering, the wavelength of the scattered X-rays increases.
Correct answer: Increases- A. Line
- B. Continuous
- C. Band
- D. All of these options are correct
Explanation: The spectrum of a black body is continuous, meaning it contains a continuous range of wavelengths without any distinct breaks or lines.
Correct answer: Continuous- A. Phosphorous
- B. Carbon
- C. Sodium
- D. X-ray phosphors absorb X-rays and emit visible light so X-ray images can be seen
Explanation: X-ray phosphors are indeed the materials commonly used in X-ray detection screens, as they absorb X-rays and emit visible light, enabling…
Correct answer: X-ray phosphors absorb X-rays and emit visible light so X-ray images can be seen- A. 900
- B. 500
- C. 1300
- D. 1600
Explanation: Platinum wire typically starts to emit a yellowish glow when heated to around 1300 degrees Celsius.
Correct answer: 1300- A. Momentum
- B. Charge
- C. Mass
- D. All of these
Explanation: Solar cells follow photovoltaic effect in which energy and momentum are conserved hence momentum is the answer.
Correct answer: Momentum