Physics MCQs

Question #81

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A car's speedometer measures:

A. Instantaneous speed

B. Average velocity

C. Average speed

D. Instantaneous velocity

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Correct Answer: Option A

Explanation:
A speedometer shows the speed of a vehicle at a particular instant in time. Speed is a scalar quantity (magnitude only, no direction). Therefore, it measures instantaneous speed. If it were measuring velocity, it would also need to display the car's current compass direction of travel at every moment.

This question belongs to: Science Physics

Question #82

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Newton's First Law of Motion is also known as the Law of:

A. Gravitation

B. Momentum

C. Action and Reaction

D. Inertia

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Correct Answer: Option D

Explanation:
Newton's First Law states that a body at rest stays at rest, and a body in motion stays in uniform motion unless acted upon by an external unbalanced force. This inherent property of matter to resist any change in its state of rest or motion is called inertia, hence it is known as the Law of Inertia.

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Question #83

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In the SI system, what are the fundamental units of momentum?

A. kg m² s⁻¹

B. kg m s⁻¹

C. kg² m s⁻¹

D. kg m s⁻²

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Correct Answer: Option B

Explanation:
Momentum (p) is defined as the product of mass (m) and velocity (v). p = m × v. The SI unit of mass is the kilogram (kg) and the SI unit of velocity is meters per second (m/s or m s⁻¹). Therefore, the SI unit of momentum is kg m/s or kg m s⁻¹.

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Question #84

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If a force of 10 N acts on a body and displaces it by 2 m in the direction of the force, the work done is:

A. 20 J

B. 12 J

C. 0 J

D. 5 J

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Correct Answer: Option A

Explanation:
Work done (W) is calculated as the dot product of force and displacement: W = F × d × cos(θ). Since the displacement is in the direction of the force, the angle θ is 0°, and cos(0°) = 1. W = 10 N × 2 m × 1 = 20 Joules (J).

This question belongs to: Science Physics

Question #85

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A thermometer reads 25°C. What is the corresponding temperature in Kelvin?

A. 298 K

B. 273 K

C. 248 K

D. 325 K

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Correct Answer: Option A

Explanation:
To convert a temperature from Celsius to Kelvin, the formula is K = °C + 273.15. For most physics problems, we use 273. Therefore, K = 25 + 273 = 298 K. Kelvin is the SI unit of temperature, and it never uses a degree symbol.

This question belongs to: Science Physics

Question #86

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A body starts from rest and moves with uniform acceleration. Which graph accurately represents its motion?

A. A decreasing straight line on a velocity-time graph.

B. A straight line displacement-time graph passing through origin.

C. A straight horizontal line on a velocity-time graph.

D. A parabolic displacement-time graph curving upwards.

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Correct Answer: Option D

Explanation:
For uniform acceleration starting from rest, the displacement equation is s = ½at². Since displacement 's' is proportional to the square of time (t²), the displacement-time graph is a parabola curving upwards. A straight horizontal line on a v-t graph means constant velocity (zero acceleration).

This question belongs to: Science Physics

Question #87

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The apparent weight of a person in an elevator moving downwards with an acceleration 'a' (where a < g) is:

A. Less than true weight

B. Greater than true weight

C. Equal to true weight

D. Zero

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Correct Answer: Option A

Explanation:
When an elevator moves downwards with acceleration 'a', the net downward force on the person is mg - R = ma, where R is the normal reaction (apparent weight). Solving for R gives R = m(g - a). Since g - a is less than g, the apparent weight (R) is less than the true weight (mg).

This question belongs to: Science Physics

Question #88

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What is the focal length of a plane mirror?

A. Infinity

B. Zero

C. Negative

D. One

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Correct Answer: Option A

Explanation:
The focal length of a spherical mirror is defined as R/2, where R is the radius of curvature. A plane mirror is essentially a part of a spherical mirror whose radius of curvature is infinity (it is completely flat). Therefore, the focal length of a plane mirror is also infinity.

This question belongs to: Science Physics

Question #89

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Assertion (A): The velocity of sound is greater in solids than in gases. Reason (R): Solids possess higher elasticity compared to gases.

A. A is false but R is true.

B. Both A and R are true but R is NOT the correct explanation of A.

C. Both A and R are true and R is the correct explanation of A.

D. A is true but R is false.

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Correct Answer: Option C

Explanation:
The velocity of sound in a medium is determined by the formula v = √(E/ρ), where E is the modulus of elasticity and ρ is the density. Although solids are denser, their modulus of elasticity (bulk modulus) is tremendously higher than that of gases, overwhelmingly compensating for the density. Hence, sound travels fastest in solids.

This question belongs to: Science Physics

Question #90

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Which of the following devices relies on the heating effect of electric current?

A. Electric fan

B. Electric generator

C. Transformer

D. Electric iron

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Correct Answer: Option D

Explanation:
An electric iron contains a heating element (usually nichrome). When electric current passes through this high-resistance element, it produces heat according to Joule's law (H = I²Rt). An electric fan uses the magnetic effect (motor), a generator uses electromagnetic induction, and a transformer uses mutual induction.

This question belongs to: Science Physics

Question #91

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If the distance between two charges is doubled, the electrostatic force between them will become:

A. Half

B. One-fourth

C. Double

D. Four times

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Correct Answer: Option B

Explanation:
According to Coulomb's Law, the electrostatic force (F) between two point charges is inversely proportional to the square of the distance (r) between them (F ∝ 1/r²). If the distance is doubled (r becomes 2r), the new force F' ∝ 1/(2r)² = 1/4r². Thus, the force becomes one-fourth of its original value.

This question belongs to: Science Physics

Question #92

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The process of splitting a heavy atomic nucleus into two lighter nuclei of comparable masses is known as:

A. Nuclear fusion

B. Isotope formation

C. Nuclear fission

D. Radioactive decay

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Correct Answer: Option C

Explanation:
Nuclear fission is the process where a heavy, unstable nucleus (like Uranium-235) is split into two smaller, stable nuclei when bombarded with a neutron. This process releases a massive amount of energy and more neutrons, triggering a chain reaction. Nuclear fusion is the opposite process (combining light nuclei).

This question belongs to: Science Physics

Question #93

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In modern household wiring, a 'fuse' has largely been replaced by which device that performs the same safety function but can be reset?

A. Capacitor

B. MCB (Miniature Circuit Breaker)

C. Inverter

D. Rectifier

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Correct Answer: Option B

Explanation:
A Miniature Circuit Breaker (MCB) serves the same safety function as a fuse: breaking the circuit during an overload or short circuit. However, unlike a fuse wire that melts and must be physically replaced, an MCB contains an electromechanical mechanism that trips the switch. It can simply be switched back on to restore power.

This question belongs to: Science Physics

Question #94

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Who formulated the Planetary Model of the atom, proposing that electrons orbit the nucleus in specific, quantized circular orbits?

A. J. J. Thomson

B. Albert Einstein

C. Niels Bohr

D. Ernest Rutherford

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Correct Answer: Option C

Explanation:
Niels Bohr proposed the Bohr model of the atom in 1913. He improved upon Rutherford's model by introducing quantum theory, suggesting that electrons travel in discrete, quantized orbits around the nucleus without radiating energy, and that energy is only emitted or absorbed when an electron jumps between these specific orbits.

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Question #95

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A satellite moves in a circular orbit around the Earth at a constant speed. The work done by the gravitational force on the satellite is:

A. Maximum

B. Zero

C. Negative

D. Positive

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Correct Answer: Option B

Explanation:
Work is defined as W = F.d.cos(θ). For a satellite in a circular orbit, the gravitational force acts as the centripetal force, directing entirely towards the center of the Earth. The displacement of the satellite at any instant is tangential. Since the angle between force and displacement is exactly 90°, cos(90°) = 0, meaning zero work is done.

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Question #96

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If a stone dropped from the top of a tower reaches the ground in 4 seconds, what is the approximate height of the tower? (Take g = 10 m/s²)

A. 40 m

B. 160 m

C. 80 m

D. 60 m

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Correct Answer: Option C

Explanation:
Using the second equation of motion for free fall: h = ut + ½gt². Since it is dropped, initial velocity (u) = 0. Time (t) = 4s, g = 10 m/s². The height h = 0 + ½(10)(4)² = 5 × 16 = 80 meters.

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Question #97

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In a simple harmonic motion (SHM), where is the kinetic energy of the oscillating particle maximum?

A. At the extreme positions

B. It remains constant everywhere

C. At the mean position

D. Halfway between mean and extreme position

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Correct Answer: Option C

Explanation:
In Simple Harmonic Motion (like a swinging pendulum), velocity is maximum when the particle passes through its equilibrium or mean position. Since Kinetic Energy = ½mv², KE is maximum at the mean position. At the extreme positions, the velocity is briefly zero, meaning kinetic energy is zero and potential energy is maximum.

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Question #98

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Which physical law explains the generation of lift force on an airplane wing?

A. Archimedes' Principle

B. Pascal's Law

C. Bernoulli's Principle

D. Boyle's Law

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Correct Answer: Option C

Explanation:
Bernoulli's principle states that an increase in the speed of a fluid occurs simultaneously with a decrease in pressure. Airplane wings (airfoils) are shaped so that air travels faster over the curved top surface than the flat bottom. This creates lower pressure above the wing and higher pressure below, resulting in an upward lift force.

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Question #99

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Rainbow formation is a complex phenomenon primarily involving which set of optical processes?

A. Reflection, Scattering, and Dispersion

B. Refraction, Dispersion, and Total Internal Reflection

C. Reflection, Diffraction, and Scattering

D. Diffraction, Interference, and Polarization

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Correct Answer: Option B

Explanation:
A rainbow is formed by sunlight interacting with water droplets. As light enters the droplet, it undergoes refraction and dispersion (separating into colors). The light then strikes the back of the droplet and undergoes total internal reflection. Finally, it undergoes a second refraction as it exits, spreading the spectrum out for the observer to see.

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Question #100

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An electrical appliance is rated 1500 W, 220 V. What is the current drawn by it?

A. 15 A

B. 4.5 A

C. 10 A

D. 6.8 A

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Correct Answer: Option D

Explanation:
The power formula is P = VI, where P is power, V is voltage, and I is current. Rearranging for current gives I = P / V. Given P = 1500 W and V = 220 V, the current I = 1500 / 220 ≈ 6.818 Amperes. Thus, 6.8 A is the closest correct answer.

This question belongs to: Science Physics

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