CAPF AC 2022 Q26: Science & Technology – Physics

CAPF AC 2022, Paper I (General Ability and Intelligence) · Science & Technology

1. (a) becomes zero
2. (b) remains same
3. (c) increases sharply
4. (d) decreases sharply

Answer: (c) increases sharply

Explanation

What happens in a short circuit

How to think: in a short circuit the live wire touches the neutral wire directly.

The current skips the appliance and finds a path of almost zero resistance.

By Ohm's law, current = voltage ÷ resistance.

When resistance falls to nearly zero, the current shoots up.

The danger: the large current heats the wires and can start a fire.

The protection: a fuse melts, or a miniature circuit breaker (MCB) trips, and cuts off the current.

Answer: (c) increases sharply.

Why each option is right or wrong

• (a) Incorrect. Current becomes zero in an open circuit, not a short circuit.
• (b) Incorrect. The current does not stay the same; the resistance has collapsed.
• (c) CORRECT. Resistance becomes almost zero, so the current increases sharply.
• (d) Incorrect. A sharp decrease would need a rise in resistance, the opposite of a short.

Key point

Short circuit: live and neutral wires touch, resistance near zero, current rises abruptly, heating and fire risk. Overloading: too many appliances on one socket. Safety devices: fuse (in series with the live wire), MCB, earthing.

Remember

Short circuit: resistance near zero, current very high.

Common mistakes

• Mixing up a short circuit (huge current) with an open circuit (no current).
• Thinking the current falls because the appliance stops working.
• Confusing short-circuiting with overloading, which has a different cause.

Exam tip

Educated guess: a short circuit blows the fuse. A fuse blows only when the current is too large.

Sources

• NCERT Class X Science — Magnetic Effects of Electric Current (domestic electric circuits)
• NCERT Class VII Science — Electric Current and its Effects (electric fuse)

Practise CAPF AC PYQsTake a timed mock