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 30 of 37
- A. Carry 1⁄4th their previous energy.
- B. Are 1/16th as numerous as before.
- C. Are 1/4th as numerous as before.
- D. Carry 1/4th their pervious momentum
Explanation: I2/I1= (r1/r2)2As r1= 0.25mAnd r2= 1m we have I2/I1=1/16This is correct based on the change in intensity.
Correct answer: Are 1/16th as numerous as before.- A. 41 keV
- B. 51 keV
- C. 61 keV
- D. 71 keV
Explanation: To determine the maximum kinetic energy of the photoelectrons, we need to calculate the energy of the incident X-rays and the energy…
Correct answer: 41 keV- A. 3 x 10^18 kg/sec
- B. 3 x 10^19 kg/sec
- C. 3 x 10^20 kg/sec
- D. 3 x 10^21 kg/sec
Explanation: This is the solution:E = mc2m = E/c2= 2.7 x 1036 /9 x 1016= 27 x 1035 /9 x 1016= 3 x 1019 kg/secTherefore, it is the correct option.
Correct answer: 3 x 10^19 kg/sec- A. 1.2 eV
- B. 1.5 eV
- C. 1.6 eV
- D. 1.8 eV
Explanation: The light used (1800 Å) is more energetic than the minimum required (2300 Å).The difference in their energies is moderate, so the emitted…
Correct answer: 1.5 eV- A. 0.48µA
- B. 0.42mA
- C. 0.48 mA
- D. 0.42µA
Explanation: For wavelength 400 nm, energy of each photon will be:E = hc/λn number of photon will have energyne = 1.5mW0.1% photons extract…
Correct answer: 0.48µA- A. 4eV
- B. 6.2 eV
- C. 2 eV
- D. 2.2 eV
Explanation: This value makes the maximum possible kinetic energy 6.2−2.2=4.0 eV, exactly the energy the field (4 V over 1 m) can remove.
Correct answer: 2.2 eV- A. 3.1 V
- B. 1.2 V
- C. Zero
- D. Infinite
Explanation: Calculate the energy of the incident photon:Use the formula: Ephoton = (hc) / λWhere:Ephoton is the energy of the photonh is Planck's…
Correct answer: 1.2 V- A. 12 x 10^18
- B. 10 x 10^18
- C. 12 x 10^17
- D. 12 x 10^16
Explanation: Energy of one photon equals h c over lambda equals 6.64 × 10⁻³⁴ joule seconds times 3 × 10⁸ meters per second divided by 6000 angstrom…
Correct answer: 12 x 10^17589. The energy of a photon corresponding to the visible light of maximum wavelength is approximately:
- A. 1 eV
- B. 1.6 eV
- C. 3.2 eV
- D. 7 eV
Explanation: Maximum wavelength of red light λ = 750 × 10⁻⁹ m.Energy E = hc / λ.E = (6.6 × 10⁻³⁴ × 3 × 10⁸) / (750 × 10⁻⁹) × 1 / (1.6 × 10⁻¹⁹).E = 1.6…
Correct answer: 1.6 eV- A. 1.2 nm
- B. 1.2 x 10^-3 nm
- C. 1.2 x 10^-6 nm
- D. 1.2 x 10^1 nm
Explanation: Energy needed to remove the proton equals 1 MeV.1 MeV equals 1 times 10 to the power 6 electron volts.1 electron volt equals 1.6 times 10…
Correct answer: 1.2 x 10^-3 nm- A. Option A
- B. Option B
- C. Option C
- D. Option D
Explanation: The inversely proportional graph correctly represents the variation of particle momentum with associated de Broglie wavelength.
Correct answer: Option D- A. Interference
- B. Electron diffraction
- C. Polarization
- D. Refraction
Explanation: The experiment shows diffraction of electron through metal crystals.In 1927, C.J. Davisson and L.H.
Correct answer: Electron diffraction- A. Intense beam of light
- B. Coherent beam of light
- C. Monochromatic beam of light
- D. All of the above
Explanation: A laser is a device that produces an intense, coherent, and monochromatic beam (made of rays) of light.
Correct answer: All of the above- A. double
- B. eight times
- C. four times
- D. half
Explanation: When the intensity of incident light is doubled, it means the number of photons striking the surface per unit time is doubled.
Correct answer: double- A. frequency of incident light
- B. intensity of incident light
- C. Both A and B
- D. none of these
Explanation: The correct answer is Option B: intensity of incident light. The maximum energy of the electrons emitted from a photoelectric cell is…
Correct answer: intensity of incident light- A. The number of electrons emitted is a quarter of the initial number
- B. The number of electrons emitted is half the initial number
- C. Each electron emitted carries one quarter of initial energy
- D. Each emitted electron carries half the initial energy
Explanation: When the distance from the light source is doubled, the intensity of light decreases according to the inverse square law.
Correct answer: The number of electrons emitted is a quarter of the initial number- A. 103 photons of wavelength 2pm (y-rays)
- B. 102 photons of wavelength 1mm (X-rays)
- C. 106 photons of wavelength 50mm (Infrared)
- D. 106 photons of wavelength 200mm (UV)
Explanation: Gamma rays are the most energetic(high frequency) EM waves with shortest wavelength.
Correct answer: 103 photons of wavelength 2pm (y-rays)- A. Lizzy told to her mother that her mother's sweater had a hole in it.
- B. Lizzy told her mother that Lizzy's sweater had a hole in it.
- C. Lizzy said her mother that the sweater had a hole in it.
- D. Lizzy told her mother that her sweater had a hole in it.
Explanation: This sentence is both grammatically correct and clear in meaning. The phrase "Lizzy's sweater" removes any confusion about whose sweater…
Correct answer: Lizzy told her mother that Lizzy's sweater had a hole in it.- A. Sonorous ... imaginative
- B. Gaudy ...humble
- C. Old-fashioned ... nostalgic
- D. Ragged ... frightening
Explanation: Old-fashioned" describes clothing that is out of style or from an earlier period, and "nostalgic" refers to a sentimental longing for the…
Correct answer: Old-fashioned ... nostalgic- A. Option A: If only I follows
- B. Option B: If only II follows
- C. Option C: If either I or II follows
- D. Option D: If neither I nor II follows
- E. Option E: If both I and II follow
Explanation: The correct answer is Option E: If both I and II follow. This is because the statement presents a situation where investors need full…
Correct answer: Option E: If both I and II follow