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UPSC Civil Services
General Science

UPSC IAS/IPS MCQ questions — History, Polity, Economy, Science, General Studies.

207 Q 5 Subjects Graduate
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Difficulty: All Easy Medium Hard 81–90 of 207
Subjects in UPSC Civil Services
Q.81 Easy General Science Physics
Which of the following is NOT a vector quantity?
A Displacement
B Temperature
C Velocity
D Acceleration
Correct Answer:  B. Temperature
EXPLANATION

Temperature is a scalar quantity as it has only magnitude. Displacement, velocity, and acceleration are vector quantities as they have both magnitude and direction.

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Q.82 Hard General Science Physics
A charged particle moves in a magnetic field. Under what condition does it move in a straight line?
A Velocity is parallel to magnetic field
B Velocity is perpendicular to magnetic field
C Magnetic field is very strong
D Particle has positive charge
Correct Answer:  A. Velocity is parallel to magnetic field
EXPLANATION

Lorentz force F = q(v × B). When v is parallel to B, the cross product is zero, so no force acts

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Q.83 Hard General Science Physics
Which phenomenon causes the sky to appear blue during daytime?
A Reflection of light
B Refraction of light
C Rayleigh scattering
D Total internal reflection
Correct Answer:  C. Rayleigh scattering
EXPLANATION

Blue light has shorter wavelength and is scattered more by atmospheric molecules (Rayleigh scattering)

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Q.84 Hard General Science Physics
A wire of resistance R is stretched to double its length. What is the new resistance?
A R
B 2R
C 4R
D R/2
Correct Answer:  C. 4R
EXPLANATION

Resistance R = ρL/A. When length doubles, L becomes 2L and area becomes A/2 (volume constant). New R = ρ(2L)/(A/2) = 4ρL/A = 4R

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Q.85 Hard General Science Physics
Which quantum number determines the shape of an orbital?
A Principal quantum number (n)
B Azimuthal quantum number (l)
C Magnetic quantum number (m)
D Spin quantum number (s)
Correct Answer:  B. Azimuthal quantum number (l)
EXPLANATION

The azimuthal quantum number (l) determines the shape of the orbital (s, p, d, f)

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Q.86 Medium General Science Physics
A convex lens of focal length 20 cm is used as a magnifying glass. If an object is placed 5 cm from the lens, what is the nature of the image?
A Real, inverted, diminished
B Virtual, erect, magnified
C Real, erect, diminished
D Virtual, inverted, magnified
Correct Answer:  B. Virtual, erect, magnified
EXPLANATION

When object is between lens and focus (u < f), a convex lens produces virtual, erect, magnified image

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Q.87 Medium General Science Physics
What is the young's modulus of a material?
A Stress/Strain
B Strain/Stress
C Force × Area
D Force/Volume
Correct Answer:  A. Stress/Strain
EXPLANATION

Young's modulus Y = Stress/Strain = (F/A)/(ΔL/L), a measure of material stiffness

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Q.88 Medium General Science Physics
Which statement about elastic collisions is correct?
A Momentum is not conserved
B Kinetic energy is conserved
C Objects always stick together
D Maximum energy is lost
Correct Answer:  B. Kinetic energy is conserved
EXPLANATION

In elastic collisions, both momentum and kinetic energy are conserved

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Q.89 Medium General Science Physics
A radioactive element has a half-life of 10 years. After 30 years, what fraction of the original sample remains?
A 1/2
B 1/4
C 1/8
D 1/16
Correct Answer:  C. 1/8
EXPLANATION

After 3 half-lives (30 years), the fraction remaining = (1/2)³ = 1/8

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Q.90 Easy General Science Physics
Which of the following has the lowest refractive index?
A Water
B Glass
C Air
D Diamond
Correct Answer:  C. Air
EXPLANATION

Air has a refractive index of approximately 1, which is the lowest among common materials

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