NCERT Solutions for Class 7th Science Chapter 3 Activity 3.6: Let us construct — Making an electric lamp glow using an electric cell or battery

Book page 28 Updated on2026-09-19

Q1.

Predict, for each arrangement, if the lamp will glow or not and write your prediction in Table 3.1.

Table 3.1: Trying to make the lamp glow
Note: The lamps are not shown glowing in any circuit

S.No.	Arrangement of Cell and Lamp	Prediction	Observation
1.
2.
3.
4.
5.
6.

Table 3.1, page 29 — the six arrangements of the cell and the lamp, redrawn from the photographs.

Answer

Use one simple rule to predict: the lamp glows only if one of its terminals is joined to one terminal of the cell and its other terminal to the other terminal of the cell — so that current has an unbroken loop to travel round.

S.No.	How the cell and lamp are joined in Table 3.1	Prediction
1.	The wire from + is joined to one lamp wire and the wire from – is joined to the other lamp wire — both joints made	Will glow
2.	Only one joint is made; the wire from – and the second lamp wire are left lying apart	Will not glow
3.	Only the – side is joined; the wire from + is left free	Will not glow
4.	Both lamp wires are joined together to the + wire at the same point; the – wire is free	Will not glow
5.	Both lamp wires are joined together to the – wire; the + wire is free	Will not glow
6.	Again one lamp wire to +, the other lamp wire to – — both joints made	Will glow

Tip: Before predicting, trace the path with your finger starting at the + terminal. If your finger can reach the – terminal only by passing through the lamp, the lamp will glow.

Q2.

Now, connect the lamp and the cell, and observe if the lamp glows or not. Note down your observation in Table 3.1. Also, for the lamps which glow, colour their glass bulbs yellow.

Table 3.1: Trying to make the lamp glow
Note: The lamps are not shown glowing in any circuit

S.No.	Arrangement of Cell and Lamp	Prediction	Observation
1.
2.
3.
4.
5.
6.

Table 3.1, page 29 — the six arrangements of the cell and the lamp, redrawn from the photographs.

Answer

On actually making the connections, the lamp glows in the arrangements at S.No. 1 and S.No. 6 and does not glow in the rest. So only those two bulbs are to be coloured yellow.

S.No.	Observation	Reason
1.	Lamp glows	Complete circuit — current goes from + through the lamp and back to –
2.	Lamp does not glow	The loop is open at the second joint, so no current flows
3.	Lamp does not glow	The + wire is free — the loop is open
4.	Lamp does not glow	Both lamp terminals touch the same wire, and the – wire is free
5.	Lamp does not glow	Both lamp terminals touch the same wire, and the + wire is free
6.	Lamp glows	Complete circuit, made the same way as in S.No. 1

Why it happens: In 1 and 6 the two terminals of the lamp are joined to two different terminals of the cell. In 4 and 5 both lamp terminals are joined to the same terminal, so there is no push from one side to the other. In 2 and 3 the loop is simply left open.

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