NCERT Solutions Curiosity Chapter 3 Activity 3.11: Let us identify — Electrical Conductors and Insulators

Book page 35 Updated on2026-09-05

Q1.

Touch the two free ends of the wires momentarily. Does the lamp glow? If yes, our tester is ready.

Answer

Yes, the lamp glows for that moment.

While the two bare ends are apart, the circuit has a gap in it and no current flows. The instant you make them touch, the metal of one wire meets the metal of the other, the loop is completed and the lamp lights up.

Ends apart → circuit open → lamp off
Ends touching → circuit closed → lamp on

This test proves that the cell, the lamp and all the joints are working. Your conduction tester is now ready — whatever you place between the two free ends will take the place of that touch.

Tip: If the lamp does not glow on touching the ends, check the cell, the bulb, and whether about 1 cm of plastic covering has really been removed from each end of every wire.

Q2.

One by one, touch the free ends of the tester's wires to both ends of each object you have collected (Fig. 3.15b). Make sure the wires don't touch each other. Does the lamp glow every time?

Answer

No. The lamp glows for some objects and stays dark for others.

It glows for the metal spoon, coin, key, pin, sewing needle, aluminium foil and pencil lead.
It does not glow for cork, rubber, glass, the plastic scale, the wooden block, the candle, cardboard and paper.

This shows that electric current can pass easily through some materials but not through others — which is exactly the point of the activity.

Check it yourself: The two wires must never touch each other while testing. If they do, current takes the short cut and the lamp glows even for a piece of wood, giving a wrong result.

Q3.

Record your observations in Table 3.3.

Answer

A completed Table 3.3 looks like this. Rows 8 and 9 are left for objects of your own choice — two useful ones are given here.

S.No.	Object	Material it is made up of	Lamp glows (Yes/No)	Conclusion (Conductor/Insulator)
1.	Stick	Wood	No	Insulator
2.	Scale	Plastic	No	Insulator
3.	Bangle	Glass	No	Insulator
4.	Paper strip	Paper	No	Insulator
5.	Candle	Wax	No	Insulator
6.	Key	Metal	Yes	Conductor
7.	Eraser	Rubber	No	Insulator
8.	Coin	Metal	Yes	Conductor
9.	Aluminium foil	Aluminium (metal)	Yes	Conductor

Try This: Test a pencil sharpened at both ends. The lamp glows through the lead (graphite) but not through the wood — one object, two different answers.

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