Home › Free notes › Class 7 Science › Electricity: Circuits and their Components

Electricity: Circuits and their Components – Class 7 Science notes, important questions and MCQs

NCERT Class 7 Science, chapter 3. Notes, key terms, important questions with answers and MCQs.

Chapter overview

An electric circuit is a closed path for current. Cells, wires, switches and bulbs are its main parts, shown with standard symbols.

Circuit basics

A cell has a positive (+) and a negative (−) terminal; a battery is two or more cells joined.
Current flows only in a closed circuit; an open switch breaks the path.
Conductors (copper, iron) let current pass; insulators (plastic, rubber, wood) do not.

Symbols and safety

Symbols: cell (long and short lines), switch, bulb, wire.
Bulbs in series: one fuse breaks all; bulbs in parallel: others keep glowing.
Never experiment with mains electricity; use only cells in school activities.

Key terms

Electric circuit: complete path through which current flows
Conductor: material that allows current to pass
Insulator: material that does not allow current to pass

Formulas

Battery = combination of cells

Important questions with answers

Name two conductors and two insulators.2 marks

Conductors: copper, iron (metals). Insulators: plastic, rubber (also wood, glass).

Why are electric wires covered with plastic?3 marks

Plastic is an insulator. It stops current from passing to our body if we touch the wire, and prevents wires from touching each other (short circuit).

Draw (describe) a simple circuit with a cell, switch and bulb using symbols. What is a battery? Why should we never touch switches with wet hands or play near high-voltage lines?5 marks

The circuit has a cell (long thin line for +, short thick line for −), a switch, and a bulb, joined in one closed loop by connecting wires. A battery is two or more cells joined together, with the positive terminal of one connected to the negative of the next. Water (with dissolved salts) conducts electricity, so wet hands can let current pass through the body and give a shock; high-voltage lines can cause severe injury or death even without touching directly.

Quick revision

Closed circuit → current flows.
Metals are good conductors.
Switch ON = circuit closed.

Exam tips

The longer line in a cell symbol is the positive terminal.
Electricians wear rubber gloves because rubber is an insulator.

Practice MCQs

Which is a conductor?
1. copper
2. plastic
3. rubber
4. wood
Show answer
Answer: (a) copper. Metal.
When a switch is OFF, the circuit is
1. closed
2. charged
3. short
4. open
Show answer
Answer: (d) open. Open.
In a cell symbol, the longer line shows the
1. negative terminal
2. positive terminal
3. switch
4. bulb
Show answer
Answer: (b) positive terminal. Positive terminal.
Why do electric wires have plastic covering?
1. to look nice
2. to carry current faster
3. plastic is an insulator and prevents shocks
4. to keep them cool
Show answer
Answer: (c) plastic is an insulator and prevents shocks. Safety.
A switch in a circuit is used to
1. open or close the circuit
2. increase current
3. store electricity
4. produce light
Show answer
Answer: (a) open or close the circuit. Makes or breaks the path.
Two bulbs are in series. If one fuses, the other
1. also stops glowing
2. glows brighter
3. glows normally
4. flickers only
Show answer
Answer: (a) also stops glowing. The single path is broken.
Why is a filament bulb's filament made of tungsten?
1. it is cheap
2. it has a very high melting point
3. it is an insulator
4. it is magnetic
Show answer
Answer: (b) it has a very high melting point. It can glow white-hot without melting.
In a torch, the bulb glows only when
1. one terminal is connected
2. the cell is reversed only
3. the switch is off
4. the circuit is closed (complete)
Show answer
Answer: (d) the circuit is closed (complete). Current needs a closed path.

All chapters of Class 7 Science

Written by Kundali IQ from standard, well-established facts to help with revision. This is not an official NCERT publication; always read your textbook too.