BPSC CCE Prelims
Physics Previous Year Questions (PYQs)

Detailed Explanation:

✅ Statement 1 – Correct: By pulling hands backwards, the goalkeeper increases the time duration over which the ball's momentum changes to zero. Since Force = rate of change of momentum (F = Δp/Δt), increasing Δt decreases the force experienced, thereby decreasing the rate of change of momentum.

❌ Statement 2 – Incorrect: Pulling hands backwards reduces the force exerted on the ball, not increases it, by extending the time of contact.

❌ Statement 3 – Incorrect: The action decreases the force exerted by the ball on hands by increasing the stopping time, as per Newton's Third Law.

Detailed Explanation:

Centripetal force is the net force directed towards the center of a circular path that keeps an object moving in circular motion.

Without centripetal force, an object would continue moving in a straight line due to inertia (Newton's first law), not along a curved path.

Examples: Tension in a string (whirling stone), gravitational force (planetary orbits), friction (car turning).

Detailed Explanation:

✅ Option 1 – Correct: Kinetic energy to heat energy conversion involves frictional force. When objects move against each other (e.g., rubbing hands, braking vehicles), friction opposes motion and converts kinetic energy into heat energy.

❌ Option 2 – Incorrect: Potential energy to sound energy conversion (e.g., ringing bell, falling object hitting ground) does not require friction; it involves vibrations and mechanical energy transfer.

❌ Option 3 – Incorrect: Chemical energy to heat energy conversion (e.g., combustion, digestion) occurs through chemical reactions, not through frictional force.

Detailed Explanation:

When a bus takes a sharp right turn, the passengers' bodies tend to continue moving in a straight line due to inertia of motion.

Since the bus turns right, the passengers experience a tendency to move in the original direction, causing them to bend towards the left side relative to the bus.

This is an application of Newton's First Law of Motion (law of inertia), which states that a body in motion continues in its state unless acted upon by an external force.

Detailed Explanation:

✅ Statement 1 – Correct: Tuning a sitar before an orchestra involves adjusting the tension of the strings to match the frequency (pitch) with other instruments, ensuring all instruments play in harmony at the same musical scale.

❌ Statement 2 – Incorrect: Amplitude determines the loudness of sound, not the tuning; adjusting tension changes frequency/pitch, not amplitude.

❌ Statement 3 – Incorrect: Intensity (energy per unit area) is related to amplitude and distance, not directly adjusted through string tuning; tuning modifies frequency only.

Detailed Explanation:

A convex lens is thicker at the center and converges light rays. When an object is placed between the lens and its focal point, it produces a magnified, upright, virtual image—the principle behind magnifying glasses.

Concave lenses and plano-concave lenses diverge light and reduce image size, while convex mirrors also produce diminished images, making them unsuitable for magnification.

Therefore, a convex lens is used in magnifying glasses, making Option 2 the correct answer.

Detailed Explanation:

Paramagnetic substances are weakly attracted by magnetic fields and have small positive susceptibility (χ > 0). Among the options, platinum is a classic paramagnetic material with unpaired electrons that align weakly with external magnetic fields.

Iron and nickel are ferromagnetic (strongly magnetic, χ >> 1000), while mercury is diamagnetic (weakly repelled, χ < 0). Other paramagnetic examples include aluminium and manganese.

Therefore, only platinum exhibits paramagnetic behavior, making Option 3 the correct answer.

Detailed Explanation:

A washing machine uses centrifugal force during the spin cycle to separate water from clothes based on density differences.

• Centrifugation Principle: High-speed drum rotation creates outward force, pushing water through perforations while retaining heavier clothes inside.
• Therefore, the washing machine operates on centrifugation, making Option 2 the correct answer.

Detailed Explanation:

The speed of light in a medium is inversely proportional to its refractive index.

• Refractive Index Values: Vacuum = 1.0, Air ≈ 1.0003, Water ≈ 1.33, Glass ≈ 1.5–1.65.
• Glass has the highest refractive index among the given options, resulting in the slowest speed of light.
• Therefore, light travels slowest through glass, making Option 3 the correct answer.

Detailed Explanation:

A vector quantity possesses both magnitude and direction, whereas a scalar quantity has only magnitude.

• Speed is a Scalar: It measures only how fast an object moves, without any directional information (e.g., 50 km/h).
• Velocity, Displacement, and Torque are Vectors: Velocity is speed with direction; displacement is change in position with direction; torque is rotational force with directional sense.
• Therefore, speed is the only scalar among the options, making Option 4 the correct answer.

Detailed Explanation:

Earth's rotation creates a centrifugal effect that opposes gravity, reducing the effective weight of objects, especially at the equator where the rotational radius is maximum.

• Apparent gravity formula: g' = g - ω²R, where ω is angular speed and R is Earth's radius at the equator.
• Increased spinning speed: Higher ω increases ω²R, thereby decreasing g' (apparent gravity).
• Weight reduction: Since weight = mg', a smaller g' directly reduces the body's weight at the equator.
• Therefore, faster Earth rotation decreases equatorial weight, making Option 1 the correct answer.

Detailed Explanation:

Galileo Galilei was the first to define speed quantitatively as distance covered per unit of time.

• Historical Context: Galileo introduced the concept during his studies on motion and kinematics in the early 17th century.
• Significance: He established speed as a measurable scalar quantity, laying the foundation for classical mechanics.
• Therefore, Galileo is credited with the first definition of speed, making Option 4 the correct answer.

Detailed Explanation:

The Theory of Relativity was formulated by Albert Einstein in two parts: Special Relativity (1905) and General Relativity (1915).

• Special Relativity: Established that the speed of light is constant and the laws of physics are the same for all non-accelerating observers.
• General Relativity: Described gravity as the curvature of spacetime caused by mass and energy, replacing Newtonian gravity.
• Therefore, Albert Einstein is the scientist who presented the theory of relativity, making Option 4 the correct answer.

Detailed Explanation:

The Thomson effect describes the generation of electromotive force (EMF) in a single conductor due to a temperature gradient along its length.

• Core Distinction: Unlike the Seebeck effect (requiring two dissimilar metals), Thomson effect occurs in a single homogeneous conductor with varying temperature.
• Mechanism: Electrons diffuse from hot to cold regions, creating a potential difference proportional to the temperature gradient.
• Therefore, potential variation due to temperature variation in a single conductor is the Thomson effect, making Option 4 the correct answer.

Detailed Explanation:

A concave mirror produces a magnified (larger) virtual image when the object is placed between the pole and focus—commonly seen in makeup/shaving mirrors.

A plane mirror always produces same-size images, a convex mirror always produces diminished images, and a cylindrical mirror with bulging side outwards distorts rather than uniformly magnifies.

Therefore, only a concave mirror produces a larger image when the person stands close enough, making Option 1 the correct answer.