NCERT Solutions Curiosity Chapter 4 –48Section 4.1 Does an Electric Current Have a Magnetic Effect? — Activity 4.1: Let us investigate
Book page 47 Updated on2026-09-05
Q1.
While watching the compass needle, move the switch to 'ON' position to allow electric current to flow through the wire (Fig. 4.1b). What do you observe?
Answer
The moment the switch is closed, the compass needle is deflected — it turns away from the north–south direction in which it was resting and settles at an angle to the wire.
Activity 4.1 — with the switch ON, the needle of the compass placed under the stretched wire turns away from north–south.
Why it happens: a current carrying wire produces a magnetic field in the region around it. The compass needle is a tiny magnet, so it is acted on by this field and swings out of its resting direction. The deflection is a signal that current is flowing — nothing touches the needle, and the effect passes straight through the cardboard between the wire and the compass, because cardboard is a non-magnetic material.
Q2.
Now again while watching the compass needle, move the switch to 'OFF' position. What do you observe this time?
Answer
The needle returns to its original direction — it swings back and once again settles along the north–south line.
Why it happens: switching OFF breaks the circuit, so the current stops. With no current there is no magnetic field around the wire, and the only magnet left acting on the needle is the Earth itself. A freely turning magnet in the Earth's field rests north–south, so that is where the needle goes back to.
Tip: notice how quickly the needle responds. The magnetic effect appears and disappears with the current — it is not stored in the wire.
Q3.
Move the switch between 'ON' and 'OFF' positions a few more times. Carefully observe how the compass needle behaves the each time.
Answer
The needle behaves the same way every time: it kicks out of the north–south direction at each ON, and comes back to it at each OFF.
Switch
Current in the wire
Magnetic field around the wire
Compass needle
ON
Flows
Present
Deflected
OFF
Does not flow
Absent
Back to north–south
Why repeating matters: a single observation could be an accident — a draught of air, or a magnet somewhere nearby. Repeating the ON–OFF cycle several times and getting the same result each time shows that the deflection is genuinely linked to the current and to nothing else. This is exactly the checking that Hans Christian Oersted did in 1820 before publishing his discovery.