- Science
- Classes 6-8
- 6 min read
Simple electric circuits
Build a safe circuit with a cell, bulb and switch, and learn about conductors, insulators and why a circuit must be closed.
Let us begin
The big idea
When you press a switch, a bulb lights up as if by magic. It is not magic. It is a circuit. A circuit is a complete path for electricity to flow around. Here we use only a small torch cell, which is safe.
An electric cell has two ends, called terminals. One is positive (+) and the other is negative (−). The cell pushes electric current around a circuit. A torch uses one or more cells.
A simple circuit has a cell, wires, a bulb and a switch. The current flows from the positive terminal through the wires and bulb and returns to the negative terminal. The bulb glows when current passes through its filament.
A circuit must make a complete loop. When the switch is ON (closed), the path is complete and the bulb glows. When the switch is OFF (open), there is a gap, so no current flows and the bulb does not glow.
Materials that let electric current pass through them are called conductors. Metals like copper, aluminium and iron are good conductors. Materials that do not let current pass are insulators. Plastic, rubber, wood, glass and cloth are insulators.
When two cells are joined one after another, the positive end of one touching the negative end of the next, the total is the sum of their voltages. Two 1.5 V cells joined this way give 3 V. SAFETY: Only ever use small cells or torch batteries for experiments. Never touch a plug point, a switch board or mains electricity. It is dangerous and can kill.
Worked examples
See how it works
Will the bulb glow?
A cell, a bulb and a switch are joined in a loop with wires. The switch is OFF. There is a gap in the loop, so the circuit is open and the bulb does not glow. When the switch is turned ON, the loop is complete and the bulb glows.
Conductor or insulator?
Test a key, an eraser, a coin and a plastic spoon in a circuit gap. The key and the coin are metal, so the bulb glows: they are conductors. The eraser and plastic spoon are insulators: the bulb stays off.
Two cells together
Two cells of 1.5 V each are joined end to end (positive to negative). Total voltage = 1.5 V + 1.5 V = 3 V. The bulb would glow brighter than with one cell, as long as the bulb is made for it.
Try it at home
Light a bulb and test conductors
You will need
- One 1.5 V torch cell
- One small torch bulb (with holder if you have one)
- Two pieces of insulated wire with the ends bare
- Sticky tape
- Things to test: coin, key, eraser, plastic spoon, paper clip, wooden stick
What to do
- Tape one wire to the (+) end of the cell, the end with the small knob, and another wire to the flat (−) end.
- Touch the free end of one wire to the bottom tip of the bulb and the free end of the other wire to the side of the bulb. The bulb should glow, so you know your circuit works.
- Now lift one wire off the bulb. Touch that wire to one end of a test object, and touch the other end of the object to the bulb, so the object is part of the loop.
- Watch the bulb. If it glows, the object is a conductor. If it stays off, it is an insulator.
- Write a table of what you tested.
Ask a grown-up: An adult should strip the wire ends and help hold the bulb. Use ONLY a single 1.5 V cell. Never use mains electricity, a plug point, a phone charger or a vehicle battery for this experiment.
Fun fact
The first electric battery was made by the Italian scientist Alessandro Volta around the year 1800.
Practice sheet
Check what you learned
Practice sheet: Simple electric circuits (Classes 6-8, Science)
- What are the two ends of a cell called?
- Name the four parts of a simple circuit that we use to light a bulb.
- Will a bulb glow if the switch is open? Why or why not?
- What is a conductor? Give one example.
- What is an insulator? Give one example.
- Which of these is a conductor: rubber, copper, wood?
- Why are electric wires covered with plastic or rubber?
- Two 1.5 V cells are joined end to end (positive to negative). What is the total voltage?
- Why must a circuit be a complete loop?
- Why should we never experiment with the mains electricity from a socket?
Answer key
Answers: Simple electric circuits
- Positive (+) and negative (−) terminals.
- A cell, wires, a bulb and a switch.
- No. An open switch leaves a gap, so the circuit is not complete and no current flows.
- A material that lets electric current pass through it, for example copper or iron.
- A material that does not let electric current pass through it, for example plastic or rubber.
- Copper.
- Plastic and rubber are insulators. They stop the current from passing to us and keep us safe.
- 1.5 V + 1.5 V = 3 V.
- The current can flow only if there is a complete path from one end of the cell to the other.
- Mains electricity is very strong and can cause serious injury or death.