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 12 of 37
- A. OR gate
- B. AND gate
- C. NOT gate
- D. XOR gate
Explanation: Correct. A NAND gate with two inputs shorted is equivalent to an AND gateIn summary, the correct option is **b.
Correct answer: AND gate- A. Photoelectric effect
- B. Compton effect
- C. Penetrating effect
- D. Diffraction
Explanation: Diffraction is a phenomenon observed when electrons are passed through a narrow slit, demonstrating their wave-like behavior as they…
Correct answer: Diffraction- A. NAND gate
- B. NOR gate
- C. OR gate
- D. XOR gate
Explanation: A NAND gate is a combination of an AND gate followed by a NOT gate. It produces a high output (logic 1) only when both of its inputs are…
Correct answer: NAND gate224. If the temperature of the black body becomes double, the intensity of radiation from it will become
- A. Double
- B. Four times
- C. Six times
- D. Sixteen times
Explanation: According to Stefan-Boltzmann law, the intensity of radiation from a black body is directly proportional to the fourth power of its…
Correct answer: Four times225. The scattering angle for which the Compton shift in wavelength is equal to the Compton wavelength is
- A. 90 degrees
- B. 0 degrees
- C. 45 degrees
- D. 180 degrees
Explanation: When the change in wavelength equals the Compton wavelength, the scattering angle is 90 degrees.\[ \lambda' - \lambda = \frac{h}{m_e c}(1…
Correct answer: 90 degrees- A. 6.4 *10^{19}
- B. 6.4 *10 Hz
- C. 1.5 *10^{15}\) Hz
- D. 1.5 * 10^{15} Hz
Explanation: Using threshold = phi*h, with phi = 6.5*1.6*10^{-19} J and h = 6.63*10^{-34} J·s, we get threshold 1.56* 10^{15}\) Hz.
Correct answer: 1.5 *10^{15}\) Hz- A. Earth
- B. Sun
- C. Galaxy
- D. Non-existent
Explanation: According to the principles of special relativity, there is no absolute standard of rest.
Correct answer: Non-existent- A. Motion can alter time but not space
- B. Motion can alter time and space
- C. Motion cannot alter both time and space
- D. None of these
Explanation: The correct answer is (b) Motion can alter time and space.According to the principles of special relativity, motion can affect both time…
Correct answer: Motion can alter time and space- A. De Broglie
- B. Einstein
- C. Stephen hawking
- D. Lewis
Explanation: Louis de Broglie, a French physicist, proposed the concept of matter waves in his 1924 PhD thesis.
Correct answer: De Broglie- A. Time dilation
- B. Mass dilation
- C. Length dilation
- D. None of these
Explanation: The twin paradox is a thought experiment in special relativity that explores the consequences of time dilation.
Correct answer: Time dilation- A. Einstein
- B. Bohr
- C. Dirac
- D. Planck
Explanation: Paul Dirac, a British physicist, proposed the existence of antimatter in 1928.
Correct answer: Dirac- A. Intensity of incident light
- B. Frequency of incident light
- C. Both a and b
- D. None of these
Explanation: The stopping potential does depend on both the intensity and frequency of the incident light.Here's why:Frequency: The frequency of the…
Correct answer: Both a and b- A. Violet
- B. Blue-green
- C. Ultraviolet
- D. Infrared
Explanation: Transition is to 2nd orbit which means we have to use the formula for Balmer series which is: 1/λ = RH (1/22 - 1/n2)For 4th orbit: 1/λ =…
Correct answer: Blue-green234. Laser light is:
- A. Monochromatic
- B. Intense
- C. Coherent
- D. All of these
Explanation: The full form of laser in literal is Light amplification by stimulated emission of radiation.
Correct answer: All of these- A. Lymann
- B. Balmer
- C. Brackett
- D. Pfund
Explanation: The series emitted is in the order from 1: (5)Lymann → Balmer → Paschen → Brackett → Pfund → HumpherySo, for 5th orbit it is Pfund series.
Correct answer: Pfund236. Total energy of an electron in hydrogen atom when it jumps to higher orbit from a lower orbit is:
- A. Less negative
- B. More positive
- C. Less positive
- D. Remains same
Explanation: We know that the total energy of an electron in orbit is negative (due to attraction towards nucleus), given by the relation En = -E0 / n2…
Correct answer: Less negative- A. Bracket
- B. Pfund
- C. Paschen
- D. None of these
Explanation: The radiation emitted by the human body is in the form of thermal radiations.
Correct answer: None of these- A. lyman visible, balmer uv
- B. lyman uv, balmer visible
- C. Lyman infrared, balmer uv
- D. Both infrared
Explanation: Lyman: UV Balmer: VisibleThe series are in the order:
Correct answer: lyman uv, balmer visible- A. 10 m/sec
- B. 1x10³ m/sec
- C. 1x10⁴ m/sec
- D. 1x10⁶ m/sec
Explanation: Photon energy E = hc/λ = (6.626 × 10⁻³⁴ × 3 × 10⁸)/(3 × 10⁻⁷) ≈ 6.626 × 10⁻¹⁹ J. Work function Φ = 1 eV = 1.602 × 10⁻¹⁹ J.
Correct answer: 1x10⁶ m/sec- A. 41 keV
- B. 51 keV
- C. 61 keV
- D. 71 keV
Explanation: Photon energy for 0.1 Å X-rays = 124 keV , while K-edge energy (0.15 Å) = 82.
Correct answer: 41 keV