Physics — Practice

Question 1

The SI unit of force is:
(a) Joule  (b) Newton  (c) Watt  (d) Pascal

Accepted Answer

Force = mass × acceleration → kg·m/s² is named the newton (N).

Answer: (b) Newton. Trap (a) Joule is the unit of work/energy (kg·m²/s²); trap (c) Watt is the unit of power (J/s); trap (d) Pascal is the unit of pressure (N/m²) — each is the correct unit for a different physical quantity, not force.

Question 2

Which instrument is used to measure atmospheric pressure?
(a) Thermometer  (b) Barometer  (c) Hygrometer  (d) Anemometer

Accepted Answer

A barometer measures atmospheric (air) pressure.

Answer: (b) Barometer. Trap (a) Thermometer measures temperature; (c) Hygrometer measures humidity; (d) Anemometer measures wind speed — all genuine instruments, but each for a different quantity.

Question 3

A book resting on a table stays at rest unless someone pushes it. This directly illustrates:
(a) Newton's Second Law  (b) Newton's Third Law  (c) Newton's First Law (Law of Inertia)  (d) Law of Conservation of Momentum

Accepted Answer

A body at rest remains at rest unless acted upon by an external force — the definition of the Law of Inertia, Newton's First Law.

Answer: (c). Trap (a) Second Law concerns F = ma once a force IS applied; trap (b) Third Law concerns action-reaction pairs, not rest; trap (d) momentum conservation is a separate principle about interacting bodies, not a single body at rest.

Question 4

A resultant force of 15 N acts on an object of mass 3 kg, initially at rest. The acceleration produced is:
(a) 5 m/s²  (b) 18 m/s²  (c) 12 m/s²  (d) 45 m/s²

Accepted Answer

a = F/m = 15/3 = 5 m/s².

Answer: (a) 5 m/s². Trap (b) 18 comes from adding F + m instead of dividing; trap (c) 12 comes from subtracting F − m; trap (d) 45 comes from multiplying F × m, confusing a = F/m with a = F×m.

Question 5

A porter lifts a trunk by applying a force of 50 N through a vertical height of 2 m. The work done is:
(a) 25 J  (b) 52 J  (c) 100 J  (d) 48 J

Accepted Answer

W = F × d = 50 × 2 = 100 J.

Answer: (c) 100 J. Trap (a) 25 divides instead of multiplying (50/2); trap (b) 52 adds F + d; trap (d) 48 subtracts F − d — none of these use the correct W = F × d relationship.

Question 6

A machine does 600 J of work in 15 seconds. Its power output is:
(a) 40 W  (b) 615 W  (c) 585 W  (d) 9000 W

Accepted Answer

P = W/t = 600/15 = 40 W.

Answer: (a) 40 W. Trap (b) 615 adds W + t; trap (c) 585 subtracts W − t; trap (d) 9000 multiplies W × t instead of dividing.

Question 7

Normal human body temperature is 37°C. Expressed on the Fahrenheit scale, this is:
(a) 37°F  (b) 66.6°F  (c) 98.6°F  (d) 310°F

Accepted Answer

F = (C × 9/5) + 32 = (37 × 1.8) + 32 = 66.6 + 32 = 98.6°F.

Answer: (c) 98.6°F. Trap (a) 37°F simply keeps the Celsius number unconverted; trap (b) 66.6°F stops after the ×9/5 step and forgets to add 32; trap (d) 310°F confuses this with the Kelvin conversion (C + 273 = 310 K) and mislabels it as Fahrenheit.

Question 8

Heat from the Sun reaches the Earth across the vacuum of space. This form of heat transfer, which needs no material medium, is:
(a) Conduction  (b) Convection  (c) Radiation  (d) Insulation

Accepted Answer

Radiation travels as electromagnetic waves and is the only mode of heat transfer that needs no material medium — exactly how solar heat crosses the vacuum of space.

Answer: (c) Radiation. Trap (a) Conduction needs direct particle contact in a solid; trap (b) Convection needs a moving fluid; trap (d) Insulation is not a mode of heat transfer at all — it is resistance to heat flow, a category-confusion trap.

Question 9

A ray of light strikes a plane mirror at an angle of 40° measured from the mirror's surface. The angle of reflection, measured from the normal, is:
(a) 40°  (b) 50°  (c) 80°  (d) 20°

Accepted Answer

The law of reflection is stated relative to the normal, not the surface. Angle from the normal = 90° − 40° = 50° (angle of incidence). Since angle of reflection = angle of incidence, the answer is 50°.

Answer: (b) 50°. Trap (a) 40° directly uses the surface angle without converting to the normal-based angle; trap (c) 80° doubles the surface angle; trap (d) 20° halves it — neither operation is the correct relationship.

Question 10

A person can focus clearly on nearby objects but not on distant ones — the image of a distant object forms in front of the retina. This defect (myopia) is corrected using a:
(a) Convex lens  (b) Concave lens  (c) Concave mirror  (d) Cylindrical lens

Accepted Answer

Myopia's image falls short of the retina; a concave (diverging) lens spreads the incoming rays slightly before they enter the eye, pushing the focus back onto the retina.

Answer: (b) Concave lens. Trap (a) Convex lens is the correction for the opposite defect, hypermetropia; trap (c) mirrors are not used for spectacle vision correction; trap (d) cylindrical lens corrects astigmatism, a different defect.

Question 11

Sound travels fastest through:
(a) Vacuum  (b) Air (a gas)  (c) Water (a liquid)  (d) Steel (a solid)

Accepted Answer

Sound is a mechanical wave that travels fastest where particles are most tightly packed — solids — followed by liquids, then gases; it cannot travel through a vacuum at all.

Answer: (d) Steel. Trap (a) Vacuum reflects the common misconception that sound behaves like light and can cross empty space — it cannot, since sound needs a medium; (b) and (c) both understate how much faster sound travels through a solid.

Question 12

The frequency range of sound audible to the average human ear is approximately:
(a) 2 Hz to 2,000 Hz  (b) 20 Hz to 20,000 Hz  (c) 200 Hz to 200,000 Hz  (d) 20,000 Hz to 200,000 Hz

Accepted Answer

The standard audible range for humans is 20 Hz to 20,000 Hz (20 kHz); below it is infrasonic, above it is ultrasonic.

Answer: (b) 20 Hz to 20,000 Hz. Trap (a) is off by a factor of 10 too low; trap (c) is off by a factor of 10 too high; trap (d) falls entirely within the ultrasonic range, confusing 'audible range' with 'ultrasonic range'.

Question 13

A resistor of 5 Ω carries a current of 3 A. The potential difference across it is:
(a) 1.67 V  (b) 8 V  (c) 15 V  (d) 2 V

Accepted Answer

V = IR = 3 × 5 = 15 V.

Answer: (c) 15 V. Trap (a) 1.67 inverts the operation (3/5 instead of 3×5); trap (b) 8 adds I + R; trap (d) 2 subtracts R − I — none apply Ohm's Law correctly.

Question 14

Two resistors of 4 Ω each are connected in parallel. Their equivalent resistance is:
(a) 8 Ω  (b) 2 Ω  (c) 4 Ω  (d) 1 Ω

Accepted Answer

1/R = 1/4 + 1/4 = 2/4 = 1/2, so R = 2 Ω.

Answer: (b) 2 Ω. Trap (a) 8 Ω wrongly adds the resistors as if in series; trap (c) 4 Ω assumes parallel connection leaves resistance unchanged; trap (d) 1 Ω over-reduces the result through a miscalculated further division.

Question 15

Which of the following will NOT increase the strength of an electromagnet?
(a) Increasing the number of turns in the coil  (b) Increasing the current through the coil  (c) Using a soft-iron core instead of an air core  (d) Reversing the direction of current flow

Accepted Answer

Reversing the current's direction reverses the electromagnet's polarity (which end is north/south) but does not change how strong it is.

Answer: (d). Traps (a), (b) and (c) are all genuine, commonly tested ways to increase an electromagnet's strength — a candidate who doesn't read 'NOT' carefully, or who misremembers which factor is which, is the intended trap here.

Question 16

Indian Navy submarines use SONAR to detect underwater objects and measure ocean depth. SONAR operates using:
(a) Radio waves  (b) Ultrasonic sound waves  (c) Infrared light  (d) X-rays

Accepted Answer

SONAR (SOund Navigation And Ranging) uses ultrasonic sound waves because sound travels efficiently through water, unlike radio waves, which are absorbed almost immediately underwater.

Answer: (b) Ultrasonic sound waves. Trap (a) Radio waves is exactly what RADAR (not SONAR) uses — the classic RADAR/SONAR mix-up; traps (c) and (d) are electromagnetic technologies not used for underwater detection.

Practice — Physics

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