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The MCQs below are drawn from the Physics subject category.
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111
Speed of light, radio waves and microwaves in vacuum is:
A. 3 × 10^8 m/s
B. 3 × 10^5 m/s
C. 3 × 10^? m/s
D. 3 × 10^6 m/s
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Correct Option
Explanation
All electromagnetic waves propagate in vacuum at the speed of light, approximately 3 × 10^8 m/s.
112
With the increase in temperature, the surface tension of a liquid
A. remains the same
B. decreases
C. increases
D. changes erratically
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Correct Option
Explanation
Surface tension typically decreases with increasing temperature because molecular cohesive forces at the surface weaken.
113
Thick tar and honey have ______ coefficient of viscosities.
A. Very short
B. Large
C. Infinite
D. Normal
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Correct Option
Explanation
Thick fluids like tar and honey have large coefficients of viscosity, so option B is correct.
114
By sucking through a straw, a student can reduce the pressure in his lungs to 750 mm Hg (density = 13.5 g/cm³). Using the straw, he can drink water from a glass up to a maximum depth of
A. 75 cm
B. 10 cm
C. 13.6 cm
D. 1.36 cm
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Correct Option
Explanation
The pressure difference is 10 mm Hg ≈ 10×13.6 mm water = 136 mm = 13.6 cm, so the max suction head is 13.6 cm.
115
Supplementary units; radian and steradian were established for
A. viscosity
B. geometrical quantities
C. electric intensity
D. density
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Correct Option
Explanation
Radian and steradian are supplementary units used for geometrical quantities (angles).
116
190. Which one is not a unit of time?
A. year
B. shake
C. leap year
D. light year
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Correct Option
Explanation
A light year is a unit of distance, not time; the others are units or measures of time, so D is correct.
117
Water flows steadily through a horizontal pipe of variable cross section. If the pressure of water is P at a point where flow speed is v, the pressure at another point where the flow speed is 2v is:
A. p - 1/2 ρ v^2
B. p - 3/2 ρ v^2
C. p - 2 ρ v^2
D. p - ρ v^2
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Correct Option
Explanation
From Bernoulli: p + 1/2ρv^2 constant, so when speed doubles dynamic pressure increases by (1/2)ρ(4v^2) = 2ρv^2, giving p2 = p - (3/2)ρv^2.
118
Unit of solid angle is called:
A. Steradian
B. Radian
C. Angstrom
D. Degree
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Correct Option
Explanation
The SI unit of solid angle is the steradian; radian is for plane angles.
119
The units of surface tension are
A. energy per unit area
B. it is dimensionless
C. same as units of force
D. force per unit area
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Correct Option
Explanation
Surface tension has SI units N/m which are equivalent to J/m^2 (energy per unit area), so option B is correct.
120
Unit of pressure is:
A. Mole
B. Watt
C. Candela
D. Pascal
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Correct Option
Explanation
The SI unit of pressure is the pascal (N/m^2).
