Dawn of Modern Physics
10 free MDCAT Physics MCQs on Dawn of Modern Physics (PM&DC syllabus), each with the answer, an explanation and the textbook line it comes from. Tap to check, no sign-up.
Tap an answer to check it · 10 questions
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Question 1
The lowest frequency of electromagnetic radiation that can cause photoelectric emission from a material is its:Show answer and explanation
Answer: C) Threshold frequency
Below it no electrons are emitted. Source: 12 Physics Book FBISE (MaryamNotes.pk), p. 138.
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Question 2
The uncertainty principle was formulated in 1927 by:Show answer and explanation
Answer: B) Werner Heisenberg
Position and momentum cannot both be known exactly. Source: 12 Physics Book FBISE (MaryamNotes.pk), p. 135.
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Question 3
Photons of energy 2.48 eV fall on a metal surface of work function 1.9 eV. The stopping potential is:Show answer and explanation
Answer: C) 0.58 V
K.E max = 2.48 - 1.9 = 0.58 eV, so V0 = 0.58 V. Source: 12 Physics Book FBISE (MaryamNotes.pk), p. 140.
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Question 4
A 50 keV X-ray photon is Compton-scattered through 90 degrees. Its energy after scattering is about:Show answer and explanation
Answer: A) 45.5 keV
lambda increases by 0.00243 nm, so energy falls to about 45.5 keV. Source: 12 Physics Book FBISE (MaryamNotes.pk), p. 140.
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Question 5
In the photoelectric effect, the maximum kinetic energy of the photoelectrons is independent of the:Show answer and explanation
Answer: B) Intensity of the light
Brighter light ejects more electrons, not faster ones. Source: 12 Physics Book FBISE (MaryamNotes.pk), p. 127.
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Question 6
If light below the threshold frequency falls on a metal, then:Show answer and explanation
Answer: D) No electrons are emitted
No matter how intense the light is. Source: 12 Physics Book FBISE (MaryamNotes.pk), p. 128.
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Question 7
Electron-positron annihilation cannot produce just one photon because it must conserve:Show answer and explanation
Answer: C) Both energy and momentum
The two photons travel in opposite directions. Source: 12 Physics Book FBISE (MaryamNotes.pk), p. 132.
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Question 8
Which phenomenon provides evidence for the particle nature of light?Show answer and explanation
Answer: D) Photoelectric effect
Interference, diffraction and polarization show its wave nature. Source: 12 Physics Book FBISE (MaryamNotes.pk), p. 132.
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Question 9
An electron microscope achieves very high resolution because fast electrons have a:Show answer and explanation
Answer: A) Very short wavelength
About 100 times shorter than visible light. Source: 12 Physics Book FBISE (MaryamNotes.pk), p. 134.
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Question 10
In an electromagnetic wave, the electric and magnetic field components are:Show answer and explanation
Answer: B) Perpendicular to each other
Both are also perpendicular to the direction of propagation. Source: 12 Physics Book FBISE (MaryamNotes.pk), p. 125.
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