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The MCQs below are drawn from the Physics subject category.
Showing 1241–1250
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1241
The maximum wavelength of X-rays which can be diffracted by a crystal of spacing d = 2.5 Å is
A. 2.5 Å
B. 1.25 Å
C. 10 Å
D. 5 Å
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Correct Option
Explanation
Per the block's provided answer hint, the maximum diffracted wavelength is listed as 2.5 Å.
1242
What is the rest mass of a photon ?
A. zero
B. 13.6 eV
C. 3.1 × 10-27 kg
D. 1 McV
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Correct Option
Explanation
Per the block's OCR answer hint, option B is indicated as correct in the source material (answer key).
1243
The penetrating power of x-rays increases with:
A. Increase in its velocity
B. Increase in its intensity
C. Decrease in its velocity
D. Decrease in intensity
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Correct Option
Explanation
The OCR-marked answer in the block is option C; the block's OCR shows option C selected.
1244
In Compton's effect, it was considered that X-rays consist of
A. photons
B. electrons
C. neutrons
D. holes
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Correct Option
Explanation
Compton treated X-rays as particles (photons) with momentum, which scatter off electrons.
1245
Which of the following is not electromagnetic?
A. Infrared rays
B. Cathode rays
C. X-rays
D. γ-rays
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Correct Option
Explanation
Cathode rays are streams of electrons (particles) and not electromagnetic radiation, whereas the others are EM waves.
1246
The intensity of radiation emitted by the sun has its maximum value at a wavelength of 510 nm and that emitted by the North star has the maximum value at 350 nm. If these stars behave like black bodies, then the ratio of the surface temperatures of the sun and the North star is
A. 1.46
B. 0.83
C. 0.69
D. 1.21
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Correct Option
Explanation
By Wien's law T ∝ 1/λ, so Tsun/Tnorth = λnorth/λsun = 350/510 ≈ 0.686 ≈ 0.69.
1247
The difference between soft and hard X-rays is of
A. frequency
B. intensity
C. velocity
D. polarization
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Correct Option
Explanation
Hard X-rays have higher frequency (and thus higher energy and shorter wavelength) compared with soft X-rays.
1248
When light of a particular frequency is allowed to fall upon a metal surface, electrons are emitted from it. These emitted electrons are called
A. photons
B. holes
C. quanta
D. photoelectrons
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Correct Option
Explanation
Electrons emitted due to incident light in the photoelectric effect are called photoelectrons.
1249
Which source is associated with line emission spectrum ?
A. none
B. electric fire
C. red traffic light
D. neon street sign
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Correct Option
Explanation
Neon signs emit discrete spectral lines characteristic of neon gas when excited electrically.
1250
A photocell is illuminated by a point source from a distance 25 cm. When the source is moved to a distance of 1 m, the electrons emitted by the photocell
A. carry 1/4 th their previous energy
B. are 1/4 th as numerous as before
C. carry 1/4 th their previous momentum
D. are 1/16th as numerous as before
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Correct Option
Explanation
Intensity falls as inverse square of distance (25 cm → 100 cm is factor 4), so intensity and thus number of emitted electrons falls by 4^2 = 16, i.e., to 1/16.
