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1181
The value of Wien's constant is:
A. 3.42 × 10^-3 m K
B. 3.34 × 10^-3 m K
C. 2.90 × 10^-3 m K
D. 4.22 × 10^-7 m K
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Correct Option
Explanation
Wien's displacement constant is approximately 2.90 × 10^-3 m·K, matching option A after OCR exponent repair.
1182
Which one of the following has the largest wavelength?
A. X-rays
B. Radiowaves
C. Visible light
D. Infrared rays
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Correct Option
Explanation
Radiowaves have the longest wavelengths among the listed types of electromagnetic radiation.
1183
In electromagnetic spectrum, X-rays are next to
A. water waves
B. ultraviolet waves
C. radiowaves
D. infrared waves
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Correct Option
Explanation
In the electromagnetic spectrum ordering, ultraviolet lies adjacent to X-rays on the lower-energy side.
1184
The energy of X-rays depends upon
A. mass of the target
B. accelerating voltage and material of the target
C. accelerating voltage
D. material of the target
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Correct Option
Explanation
X-ray energies depend on the accelerating voltage (setting the maximum photon energy) and the target material (which determines characteristic line energies).
1185
The maximum range of radar can be increased by increasing the peak transmitted power and increasing
A. The radius of the antenna
B. The diameter of the antenna
C. The radius of the focus
D. None of these
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Correct Option
Explanation
Increasing antenna diameter improves gain and effective radiated power, thereby increasing radar range.
1186
An example of continuous spectrum is
A. the photoelectric effect
B. blackbody radiation spectrum
C. skin effect
D. Compton effect
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Correct Option
Explanation
A blackbody radiation spectrum is continuous, covering a continuous range of wavelengths.
1187
X-rays can cause fluorescence in materials such as
A. cadmium
B. palatinocyanide
C. zinc sulphide
D. all of these
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Correct Option
Explanation
X-rays can induce fluorescence in various phosphors and salts (including platinocyanide and zinc sulphide), so all listed materials may fluoresce.
1188
Operation of a LASER depends upon
A. the existence of atoms in normal state
B. spontaneous emission of radiation
C. the existence of atoms in metastable state
D. the existence of atoms in ground state
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Correct Option
Explanation
Laser action requires population inversion, which relies on atoms in metastable excited states to allow stimulated emission.
1189
The optical fibre is covered for protection by a:
A. Plastic Jacket
B. Aluminium Jacket
C. Copper Jacket
D. Glass Jacket
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Correct Option
Explanation
Optical fibres are commonly protected with a plastic jacket, and the OCR marks option B.
1190
A radiation of longer wavelength:
A. Possesses high energy
B. Is available at high temperature
C. Possesses low energy
D. Is available at low temperature
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Correct Option
Explanation
Energy of a photon is inversely proportional to wavelength (E = hc/λ), so longer wavelength corresponds to lower energy.
