Physics MCQs

Question #21

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If the radius of the earth shrinks by 1%, its mass remaining the same, the value of 'g' on the earth's surface would:

A. Increase by 2%

B. Increase by 1%

C. Decrease by 1%

D. Decrease by 2%

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Correct Answer: Option A

Explanation:
The acceleration due to gravity is given by g = GM/R². For a small change, taking the derivative or using error approximation: Δg/g = -2(ΔR/R). If R shrinks by 1% (ΔR/R = -1%), then Δg/g = -2(-1%) = +2%. Therefore, the value of 'g' will increase by approximately 2%.

This question belongs to: Science Physics

Question #22

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A body weighs 72 N on the surface of the Earth. What is the gravitational force on it at a height equal to half the radius of the Earth?

A. 16 N

B. 32 N

C. 72 N

D. 28 N

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Correct Answer: Option B

Explanation:
Weight on surface W = mg = 72 N. Acceleration due to gravity at height h is g' = g [R / (R+h)]². Here h = R/2. So, g' = g [R / (R + R/2)]² = g [1 / (3/2)]² = g (2/3)² = 4g/9. The new weight W' = mg' = m(4g/9) = (4/9)mg = (4/9) × 72 = 32 N.

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Question #23

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The escape velocity for a projectile on the Earth's surface is 11.2 km/s. If a body is projected at twice this velocity, what happens?

A. It escapes Earth's gravity but eventually comes to rest in deep space.

B. It escapes Earth's gravity and retains a finite positive velocity in interstellar space.

C. It orbits the Earth indefinitely.

D. It returns to Earth after a long time.

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Correct Answer: Option B

Explanation:
Escape velocity (Ve) is the minimum velocity needed to overcome Earth's gravitational pull so that final velocity at infinity is zero. If launched with velocity v > Ve, the body will escape and, due to conservation of energy, retain a residual speed (v_infinity) at an infinite distance, calculated by v_infinity = √(v² - Ve²). Here, v = 2Ve, so it retains speed.

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Question #24

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What happens to the pressure of a given mass of gas if its volume is halved at a constant temperature?

A. It is halved.

B. It remains unchanged.

C. It is quadrupled.

D. It is doubled.

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Correct Answer: Option D

Explanation:
According to Boyle's Law, for a given mass of an ideal gas at constant temperature, the pressure is inversely proportional to its volume (P ∝ 1/V, or P1V1 = P2V2). If the volume is halved (V2 = V1/2), the pressure must double (P2 = 2P1) to keep the product constant.

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Question #25

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Hydraulic brakes used in automobiles operate on the basis of:

A. Archimedes' Principle

B. Newton's Law of Viscosity

C. Bernoulli's Theorem

D. Pascal's Law

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Correct Answer: Option D

Explanation:
Hydraulic brakes operate on Pascal's Law. It states that an external pressure applied to an enclosed, incompressible fluid is transmitted undiminished equally in all directions throughout the fluid volume. When force is applied to the small brake pedal cylinder, it exerts a large pressure that is transmitted to the larger wheel cylinders, amplifying the force.

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Question #26

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A piece of ice is floating in a glass beaker containing water. When all the ice melts, the level of water in the beaker will:

A. Fall

B. Rise

C. First rise, then fall

D. Remain the same

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Correct Answer: Option D

Explanation:
According to Archimedes' principle, the floating ice displaces a volume of water equal to its own weight. When the ice melts, it transforms into a volume of water that is exactly equal to the volume of water it displaced while floating. Therefore, the water level remains unchanged.

This question belongs to: Science Physics

Question #27

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An iron needle sinks in water, whereas an iron ship floats. This is because:

A. The weight of the water displaced by the ship is greater than the weight of the ship.

B. The average density of the ship is less than that of water.

C. The density of the ship is greater than that of the needle.

D. The ship is hollow.

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Correct Answer: Option B

Explanation:
Though the ship is made of iron, it is hollow inside and traps a large volume of air. This makes the overall or average density of the ship less than the density of water. According to the law of floatation, an object floats if its average density is less than that of the fluid. A solid iron needle has a higher density than water, so it sinks.

This question belongs to: Science Physics

Question #28

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The specific heat capacity of water is exceptionally high. This property is primarily responsible for:

A. Water having high surface tension.

B. Water being a good conductor of electricity.

C. Water expanding upon freezing.

D. The formation of sea breezes and land breezes.

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Correct Answer: Option D

Explanation:
Water has a specific heat capacity of 4184 J/kg·K, which is very high. This means it heats up and cools down much more slowly than land. During the day, land heats faster than the sea, causing air above it to rise and cool air from the sea to rush in (sea breeze). The reverse happens at night (land breeze).

This question belongs to: Science Physics

Question #29

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Why does a metal spoon feel colder than a wooden spoon when left in a cold room, despite both being at the same room temperature?

A. Metal is a poorer conductor of heat than wood.

B. Metal absorbs coldness from the air faster.

C. The specific heat of metal is higher than that of wood.

D. Metal is a better conductor of heat than wood.

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Correct Answer: Option D

Explanation:
Both spoons are at the same temperature. However, metal is a good conductor of heat. When you touch it, it rapidly conducts heat away from your hand, making your skin feel a sudden drop in temperature (which you perceive as 'cold'). Wood is a poor conductor, so it draws heat from your hand very slowly.

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Question #30

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The phenomenon by which heat is transferred through empty space without the need for a material medium is known as:

A. Conduction

B. Radiation

C. Convection

D. Latent Heat Transfer

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Correct Answer: Option B

Explanation:
Thermal radiation is the transfer of heat via electromagnetic waves (primarily infrared). Unlike conduction (which requires physical contact) or convection (which requires fluid movement), radiation can travel through a vacuum. This is how the heat from the Sun reaches the Earth through the vacuum of space.

This question belongs to: Science Physics

Question #31

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The amount of heat required to change the state of 1 kg of a substance from solid to liquid at its melting point without any change in temperature is called:

A. Specific heat capacity

B. Latent heat of vaporization

C. Latent heat of fusion

D. Thermal capacity

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Correct Answer: Option C

Explanation:
The heat required to change a solid into a liquid at its melting point without a temperature rise is called the Latent Heat of Fusion. The word 'latent' means hidden, because this heat energy breaks intermolecular bonds to change the phase rather than increasing the kinetic energy (temperature) of the molecules.

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Question #32

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Which characteristic of a sound wave determines its pitch?

A. Velocity

B. Amplitude

C. Wavelength

D. Frequency

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Correct Answer: Option D

Explanation:
The pitch of a sound is a subjective sensation that is determined primarily by the frequency of the sound wave. Higher frequency waves are perceived as high-pitched sounds (like a whistle), while lower frequency waves are perceived as low-pitched sounds (like a bass drum). Amplitude determines the loudness of the sound.

This question belongs to: Science Physics

Question #33

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SONAR is based on the principle of:

A. Diffraction of sound waves

B. Reflection of sound waves

C. Polarization of sound waves

D. Refraction of sound waves

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Correct Answer: Option B

Explanation:
SONAR (Sound Navigation and Ranging) relies on the reflection of ultrasonic waves. A transmitter sends out sound waves, which travel through water, strike an object (like a submarine or the seabed), and reflect back as an echo to a receiver. By measuring the time taken for the echo to return, the distance can be calculated.

This question belongs to: Science Physics

Question #34

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What is the minimum distance required to hear a distinct echo? (Assuming speed of sound in air is 344 m/s)

A. 10 meters

B. 17.2 meters

C. 34.4 meters

D. 25.6 meters

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Correct Answer: Option B

Explanation:
The human ear retains the sensation of sound for about 0.1 seconds (persistence of hearing). To hear a distinct echo, the reflected sound must reach the ear after at least 0.1 s. Distance traveled by sound = Speed × Time = 344 m/s × 0.1 s = 34.4 m. Since this is the total distance (go and return), the minimum distance to the obstacle is 34.4 / 2 = 17.2 meters.

This question belongs to: Science Physics

Question #35

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When an ambulance with a blaring siren moves towards an observer, the pitch of the siren appears to be higher. This is due to:

A. Acoustic resonance

B. The Doppler Effect

C. Reverberation

D. Interference of sound waves

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Correct Answer: Option B

Explanation:
The Doppler Effect is the apparent change in the frequency (and thus pitch) of a wave due to the relative motion between the source and the observer. As the ambulance approaches, sound waves get compressed, increasing the perceived frequency (higher pitch). As it moves away, waves stretch, lowering the frequency.

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Question #36

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A light ray enters from air into glass. How does its speed, frequency, and wavelength change?

A. Speed decreases, frequency decreases, wavelength decreases.

B. Speed remains same, frequency decreases, wavelength increases.

C. Speed increases, frequency remains same, wavelength increases.

D. Speed decreases, frequency remains same, wavelength decreases.

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Correct Answer: Option D

Explanation:
When light passes from a rarer medium (air) to a denser medium (glass), its speed decreases due to the higher refractive index. Wavelength is directly proportional to speed, so it also decreases. However, the frequency depends only on the source of light and remains absolutely constant during refraction across any boundary.

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Question #37

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A concave mirror forms a virtual, erect, and magnified image. Where is the object placed?

A. Between the pole (P) and the focus (F)

B. Beyond the center of curvature (C)

C. At the focus (F)

D. Between the center of curvature (C) and the focus (F)

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Correct Answer: Option A

Explanation:
A concave mirror forms real and inverted images in most positions. The only exception is when the object is placed very close to the mirror, specifically between the pole (P) and the principal focus (F). In this position, the reflected rays diverge, forming a virtual, erect, and magnified image behind the mirror. This is why concave mirrors are used as shaving or makeup mirrors.

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Question #38

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Which defect of vision is correctly matched with its correcting lens?

A. Hypermetropia - Concave lens

B. Myopia - Concave lens

C. Myopia - Convex lens

D. Presbyopia - Cylindrical lens

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Correct Answer: Option B

Explanation:
Myopia (near-sightedness) occurs when the image is focused in front of the retina. It is corrected using a concave (diverging) lens. Hypermetropia (far-sightedness) is corrected with a convex (converging) lens. Astigmatism is corrected with a cylindrical lens. Presbyopia is usually corrected with bifocal lenses.

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Question #39

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When white light passes through a glass prism, it splits into a spectrum of seven colors. Which color deviates the least?

A. Yellow

B. Violet

C. Red

D. Blue

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Correct Answer: Option C

Explanation:
Dispersion occurs because different colors of light travel at slightly different speeds inside the glass prism, meaning they have different refractive indices. Red light has the longest wavelength, the lowest refractive index in glass, and therefore deviates (bends) the least. Violet has the shortest wavelength and deviates the most.

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Question #40

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The sparkling of a diamond is primarily due to:

A. Interference

B. Dispersion

C. Total internal reflection

D. Scattering

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Correct Answer: Option C

Explanation:
Diamonds are cut in such a way that light entering them hits multiple facets from the inside at an angle greater than the critical angle (which is very low for diamond, around 24.4°). This results in multiple total internal reflections, trapping light and forcing it out of specific faces, creating a brilliant sparkle.

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