General Science — Physics — Practice

Question 1

The SI unit of power is:
(a) joule (b) watt (c) newton (d) pascal

Accepted Answer

(b) watt.

Power = work/time = joule/second = watt. Joule measures energy, newton force, pascal pressure.

Question 2

Sound travels fastest in:
(a) vacuum (b) air (c) water (d) steel

Accepted Answer

(d) steel.

Sound needs a medium (zero speed in vacuum) and moves fastest in solids: ~5000 m/s in steel vs ~1500 m/s in water and ~340 m/s in air.

Question 3

Myopia (short-sightedness) is corrected by using a:
(a) convex lens (b) concave lens (c) cylindrical lens (d) bifocal lens

Accepted Answer

(b) concave lens.

The myopic eye focuses images in front of the retina; a diverging (concave) lens pushes the focus back. Hypermetropia takes convex; astigmatism takes cylindrical.

Question 4

Which device converts electrical energy into mechanical energy?
(a) generator (b) transformer (c) electric motor (d) dynamo

Accepted Answer

(c) electric motor.

Motor: electrical → mechanical. Generator/dynamo do the reverse via electromagnetic induction; a transformer only changes AC voltage levels.

Question 5

An electric fuse works on the principle of the:
(a) magnetic effect of current (b) heating effect of current (c) chemical effect of current (d) induction effect

Accepted Answer

(b) heating effect of current.

Overload current heats the low-melting fuse wire until it melts and breaks the circuit. Electric bells use the magnetic effect; electroplating the chemical effect.

Question 6

The sky appears blue because of the:
(a) reflection of sunlight by the sea (b) scattering of sunlight by air molecules (c) dispersion of light by water droplets (d) refraction of light in the atmosphere

Accepted Answer

(b).

Rayleigh scattering by air molecules is strongest for shorter (blue) wavelengths. Dispersion by droplets makes rainbows; refraction makes stars twinkle — each phenomenon has its own principle.

Question 7

A rocket works on the principle of:
(a) Newton's first law (b) conservation of momentum (c) Bernoulli's theorem (d) Archimedes' principle

Accepted Answer

(b) conservation of momentum (equivalently Newton's third law).

High-speed exhaust carries momentum downward; the rocket gains equal momentum upward. It needs no air to push against — rockets work best in vacuum.

Question 8

One kilowatt-hour (kWh) is the unit of:
(a) power (b) energy (c) force (d) charge

Accepted Answer

(b) energy.

kWh = power × time, i.e., energy: 1 kWh = 3.6 × 10⁶ J. It is the 'unit' on electricity bills. Watt alone is power — the standard trap.

Question 9

Water has its maximum density at:
(a) 0 °C (b) 4 °C (c) 100 °C (d) −4 °C

Accepted Answer

(b) 4 °C.

Water contracts on cooling only down to 4 °C, then expands. That is why lakes freeze from the top while denser 4 °C water sinks — letting aquatic life survive beneath the ice.

Question 10

The escape velocity from the Earth's surface is approximately:
(a) 7.9 km/s (b) 9.8 km/s (c) 11.2 km/s (d) 15 km/s

Accepted Answer

(c) 11.2 km/s.

Escape velocity is the minimum launch speed to leave Earth's gravity without further propulsion. 7.9 km/s is the orbital velocity near Earth's surface — the paired distractor; 9.8 borrows the number from g.

Question 11

The frequency range audible to the human ear is:
(a) 2 Hz – 2 kHz (b) 20 Hz – 20 kHz (c) 200 Hz – 200 kHz (d) 20 kHz – 200 kHz

Accepted Answer

(b) 20 Hz – 20 kHz.

Below 20 Hz is infrasonic (earthquake waves); above 20 kHz is ultrasonic — used by bats, SONAR and medical ultrasound imaging.

Practice — General Science — Physics

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