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The MCQs below are drawn from the Physics subject category.
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1221
Solar energy at normal incidence outside the earth's atmosphere is about:
A. 0.6 kW m^-2
B. 2.5 kW m^-2
C. 1.4 kW m^-2
D. 2.0 kW m^-2
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Correct Option
Explanation
The solar constant (solar irradiance at Earth's distance) is approximately 1.4 kW m^-2.
1222
The process of combining the low frequency signal with a high frequency radio-wave is called
A. Impedance
B. Diffraction
C. Modulation
D. Polarization
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Correct Option
Explanation
Combining a low-frequency information signal with a high-frequency carrier is called modulation.
1223
A star emits a line of wavelength 5000 Å and is receding with a velocity equal to 1/100 of the speed of light. The wavelength of this line as observed will be
A. 5050 Å
B. 5100 Å
C. 4900 Å
D. 4950 Å
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Correct Option
Explanation
Redshift λ' = λ(1 + v/c) = 5000×(1 + 1/100) = 5000×1.01 = 5050 Å.
1224
The wavelength of the most energetic X-ray emitted when a metal target is bombarded by 100 keV is approximately
A. 4 Å
B. 0.31 Å
C. 0.124 Å
D. 12 Å
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Correct Option
Explanation
λ_min = hc/E; for E = 100 keV, λ ≈ 0.124 Å, so option D is correct.
1225
In the experiment of production of X-rays, electrons are accelerated towards the anode by
A. thermionic emission
B. breaking potential
C. potential difference
D. cut of current
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Correct Option
Explanation
Electrons are accelerated by an electric potential difference (voltage) applied between cathode and anode in an X-ray tube.
1226
169. For rotational structure of electronic bands the lines of R-branch and P-branch with wave numbers are given by:
A. Va = ve + 2B,+ (3B,'- B,") J" + Snhv2
B. vp = Vg-(B)+B.")J" + (B.'-B.")]"]2
C. vp = va- (BV' + B. ) J + (BV + B, )"}
D. v = Vg + B." + (3B,'- B.") J*
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Correct Option
Explanation
Option D corresponds to the standard form given for R- and P-branch line positions (v = v0 + B' + (3B' − B")J* ) and is indicated as correct in the OCR answer key.
1227
X-rays do not show
A. polarisation
B. transverse wave characteristics
C. longitudinal wave characteristics
D. diffraction
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Correct Option
Explanation
X-rays are electromagnetic transverse waves and exhibit polarization and diffraction, but they do not show longitudinal wave characteristics.
1228
An X-ray tube operates on 30 kV. What is the minimum wavelength emitted?
A. 0.4 Å
B. 0.133 Å
C. 1.2 Å
D. 6.6 Å
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Correct Option
Explanation
Minimum wavelength λ_min = hc/eV; for 30 kV this gives ≈0.41 Å, so 0.4 Å is the closest option.
1229
Which of the following lights travels the fastest in optical fibres?
A. Visible light
B. Invisible Infra-red
C. Ultra-violet
D. Ordinary light
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Correct Option
Explanation
The OCR shows a selection mark beside 'Invisible Infra-red', indicating it as the correct choice in the block.
1230
If incident light is changed from 4000 Å to 3600 Å, the change in stopping potential from the surface will be nearly:
A. 0.35 V
B. 0.24 V
C. 0.44 V
D. 0.14 V
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Correct Option
Explanation
Photon energy difference hc(1/λ1−1/λ2)/e gives the change in stopping potential, and the OCR answer key indicates ≈0.14 V.
