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 32 of 37
- A. X = 0 V.
- B. X = 2 V.
- C. X > 2 V.
- D. 0 V < X < 2 V.
Explanation: The energy of light is inversely related to its wavelength, according to the equation E = hc/λ, where h is Planck's constant, c is the…
Correct answer: X = 0 V.- A. Inversely proportional to the frequency of the incident light.
- B. Directly proportional to the frequency of the incident light.
- C. Inversely proportional to the intensity of the incident light.
- D. Directly proportional to the intensity of the incident light.
Explanation: In the photoelectric effect, the number of photoelectrons ejected from a metallic surface is directly proportional to the intensity of the…
Correct answer: Directly proportional to the intensity of the incident light.- A. Pair production.
- B. Pair annihilation.
- C. Compton's effect.
- D. Uncertainty principle.
Explanation: The correct answer is Compton's effect. This phenomenon occurs when X-rays are scattered by electrons, resulting in a change in the…
Correct answer: Compton's effect.- A. Increase the frequency of the incident light
- B. Decrease the frequency of the incident light
- C. Increase the intensity of the incident light
- D. Use a different material with a higher work function
Explanation: The photoelectric effect occurs when photons with energy equal to or greater than the material's work function strike the surface and…
Correct answer: Increase the frequency of the incident light- A. Compton effect.
- B. Pair production.
- C. Photoelectric effect.
- D. Annihilation of matter.
Explanation: The correct answer is annihilation of matter. This process involves the collision of a particle with its antiparticle, leading to their…
Correct answer: Annihilation of matter.- A. Velocity of photons.
- B. Threshold frequency.
- C. Intensity of light source.
- D. Frequency of light source.
Explanation: In the photoelectric effect, the number of photoelectrons ejected from a material is increased by increasing the intensity of the light…
Correct answer: Intensity of light source.- A. I. Compton's effect and II. photoelectric effect.
- B. I. Compton's effect and IV. pair production of matter.
- C. II. Photoelectric effect and III. annihilation of matter.
- D. III. Annihilation of matter and IV. pair production of matter.
Explanation: Einstein's mass-energy relation, expressed as E=mc², is experimentally proven by phenomena that involve the conversion between mass and…
Correct answer: III. Annihilation of matter and IV. pair production of matter.- A. 0.25 V
- B. 0.5 V
- C. 1.0 V
- D. 2.0 V
Explanation: The stopping potential in a photocell is related to the intensity of light falling on it.
Correct answer: 0.25 V- A. Intensity of incident light.
- B. Nature of emitter material.
- C. Frequency of incident light.
- D. Potential difference in the power source.
Explanation: The correct answer is the intensity of incident light. The work function is a property of the material and is related to the minimum…
Correct answer: Intensity of incident light.- A. Zero
- B. Maximum
- C. Infinity
- D. Minimum
Explanation: The formula that relates an object's mass ( m ) to its velocity ( v ) as it approaches the speed of light ( c ) is given by the…
Correct answer: Infinity- A. Alpha particle
- B. Neutron
- C. Proton
- D. Electron
Explanation: The alpha particle would have the smallest de Broglie wavelength because it has the highest mass.
Correct answer: Alpha particle- A. Electrons
- B. Protons
- C. Photons
- D. Neutrons
Explanation: According to quantum theory, radiation must appear in the form of discrete packets of energy called quanta (or photons).Here's a…
Correct answer: Photons- A. become zero.
- B. remain the same.
- C. shift towards longer wavelength.
- D. shift towards shorter wavelength.
Explanation: When the temperature of a black body is raised, the wavelength corresponding to maximum intensity shifts towards a shorter wavelength.
Correct answer: shift towards shorter wavelength.634. When the filament in a cathode rays oscilloscope (CRO) is heated, then the emitted particles are
- A. protons
- B. neutrons
- C. electrons
- D. positrons
Explanation: When the filament in a cathode rays oscilloscope (CRO) is heated, it releases electrons.
Correct answer: neutrons- A. infinite
- B. discrete
- C. continuous
- D. discontinuous
Explanation: The correct answer is 'discrete.' When a hot body emits radiations, the wavelengths are specific and distinct for each temperature…
Correct answer: discrete636. Laser can only be produced if an atom is in itsI. normal stateII. excited stateIII. ionized state
- A. I only
- B. II only
- C. I and III
- D. II and III
Explanation: The correct answer is option B: II only. Lasers can only be produced when an atom is in its excited state.
Correct answer: II only- A. long wavelength.
- B. short wavelength.
- C. infinite wavelength.
- D. moderate wavelength.
Explanation: The correct answer is Option A:long wavelength.At lower temperatures, the thermal radiations emitted have longer wavelengths because the…
Correct answer: long wavelength.- A. rest mass.
- B. inertial mass.
- C. active gravitational mass.
- D. passive gravitational mass.
Explanation: In the special theory of relativity, when an object is at rest position with respect to an observer, the mass of the object is called the…
Correct answer: rest mass.- A. becomes twice.
- B. becomes enlarged.
- C. remains unchanged.
- D. becomes contracted
Explanation: In the special theory of relativity, length contraction is a phenomenon where an object's length appears shorter when it is moving at…
Correct answer: becomes contracted- A. T3 > T2 > T1
- B. T1 > T2 > T3
- C. T2 > T1 > T3
- D. T1 > T3 > T2
Explanation: The correct answer is Option A: T3 > T2 > T1. This relationship is determined by comparing the slopes of the lines on the…
Correct answer: T3 > T2 > T1