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 8 of 37
- A. As intensity increases, the photoelectric current increases
- B. As the intensity increases, the photoelectric current decreases
- C. As the intensity decreases, the photoelectric current becomes twice
- D. No effect
Explanation: Since each incident photon ejects one photoelectron from a metal surface, therefore, the number of photoelectrons emitted depends on the…
Correct answer: As intensity increases, the photoelectric current increases- A. As intensity increases, stopping potential increases linearly
- B. As intensity increases, stopping potential decreases linearly
- C. As intensity decreases, stopping potential increases exponentially
- D. No effect
Explanation: Changing the intensity of incident radiation does not affect the stopping potential.
Correct answer: No effect- A. frequency of incident light
- B. Intensity of incident light
- C. nature of cathode rays
- D. none of these
Explanation: Kinetic energy of photo electrons does not depend upon intensity of light but it depends upon energy (frequency) of photon
Correct answer: frequency of incident light- A. Four times
- B. Double
- C. Half
- D. Zero
Explanation: When the frequency of incident light is halved of its original value i.e. 1.5vo then it becomes less than the threshold value.
Correct answer: Zero- A. Option A
- B. Option B
- C. Option C
- D. Option D
Explanation: Photoelectric current ∝ Intensity of incident light In the photoelectric effect, the photoelectric current is directly proportional to the…
Correct answer: Option A- A. Option A
- B. Option B
- C. Option C
- D. Option D
Explanation: From the incident photon energy, the electron needs a certain minimum energy called the work function "Φ" to escape from the metal surface…
Correct answer: Option D- A. One
- B. More than two
- C. Two
- D. Electron emission is not possible
Explanation: Here incident energy of photon < work function So, the photoelectric effect will not start.
Correct answer: Electron emission is not possible- A. Compton equation
- B. Plank's equation
- C. Newton's equation
- D. Photoelectric equation
Explanation: The photoelectric equation is hf=hfo +K.E. (max) The above equation is also called Einstein's photoelectric equation.
Correct answer: Photoelectric equation- A. λo/4
- B. λo/2
- C. 2 λo
- D. 4 λo
Explanation: The explanation is given below: Work function = Wo = hc/λoIf work function is Wo/2 = hc/λ1Then λ1 = 2λ0
Correct answer: 2 λo150. For the pair production phenomenon to occur the photon must have energy, greater than or equal to _
- A. 0.51 MeV
- B. 1.02 MeV
- C. 0.32 MeV
- D. 0.85 MeV
Explanation: In pair production, a proton with energy, greater than or equal to 1.02 MeV is required to create a pair of electron and positron.
Correct answer: 1.02 MeV- A. Visible light photon
- B. X-ray photon
- C. Y-ray photon
- D. U.V. photon
Explanation: When a Y-ray photon passes close to an atomic nucleus and it possesses energy greater than 1.02 MeV, the photon is converted into…
Correct answer: Y-ray photon- A. Ee= 1.02 MeV, Ep=1.02 MeV
- B. Ee= 0.51 MeV, Ep=1.02 MeV
- C. Ee= 1.02 MeV, Ep=0.51 MeV
- D. Ee= 0.51 MeV, Ep=0.51 MeV
Explanation: The explanation is given below: The rest mass energy for both electron and positron is 0.51 MeV.
Correct answer: Ee= 0.51 MeV, Ep=0.51 MeV- A. 4.1 MeV
- B. 2.05 MeV
- C. 1.02 MeV
- D. 0.51 MeV
Explanation: We know, that in pair production momentum and energy are conserved. By conserving energy, E total = Ee + Ep 4.1 MeV = Ee + Ep Now, by…
Correct answer: 2.05 MeV- A. Maxwell
- B. Hertz
- C. Einstein
- D. Heisenberg
Explanation: The photoelectric effect was discovered in 1887 by the German physicist Heinrich Rudolf Hertz.
Correct answer: Hertz- A. Pressure
- B. Temperature
- C. Intensity
- D. Frequency
Explanation: The frequency of the light determines the maximum kinetic energy of the emitted electrons.
Correct answer: Frequency- A. Maxwell
- B. Hertz
- C. Einstein
- D. Bohr
Explanation: The scientist who first explained how a photon can transfer its energy into an electron was Albert Einstein.
Correct answer: Einstein157. A change in energy of a photon occurs when it collides with an electron at rest and is known as:
- A. Photoelectric effect
- B. Compton effect
- C. Pair conduction
- D. Annihilation
Explanation: In the Compton effect, the photon collides with an electron at rest and transfers some of its energy to the electron.
Correct answer: Compton effect- A. Photoelectric effect
- B. Compton effect
- C. Pair production
- D. Diffraction
Explanation: The correct answer is diffraction. Diffraction is a phenomenon in which light bends around obstacles or through slits, which is a…
Correct answer: Diffraction- A. Neutron
- B. Proton
- C. Photon
- D. Positron
Explanation: The positron is a particle with the same mass as an electron but with the opposite charge.
Correct answer: Positron- A. Zero
- B. Less than speed of positron
- C. Equals to speed of positron
- D. Greater than speed of positron
Explanation: In electron-positron pair production, a photon with energy greater than or equal to 1.02 MeV (the rest mass energy of an electron and a…
Correct answer: Equals to speed of positron