Electricity: Circuits and their Components
Why This Matters
Think about a torch. You slide its switch one way, and the lamp lights up. You slide it back, and the lamp goes dark.
It feels like magic. But it is not magic at all. It is science, and it is simple once you see how it works.
Look around you right now. A fan spinning. A bulb glowing. A phone charging. A TV playing. All of these run on electricity. We use it every single moment of the day.
But how does electricity actually make a bulb glow? Why does flicking a switch turn a light on and off? In this chapter, we will build a small circuit ourselves, step by step. By the end, you will understand exactly what is happening inside that torch — and inside the lights at your home too.
Safety first. In this chapter we only use small cells and batteries — like the ones inside a torch, a wall clock, or a TV remote. These are safe to play with. But the electricity in your wall sockets at home is very, very strong. It can hurt you badly or even kill you. Never do experiments with the wires or sockets in your house or school. Use only torch cells and batteries.
The Big Idea
Electricity needs a complete path to flow. Picture a closed loop, like a circle, that starts at a cell, goes through wires and a bulb, and comes back to the cell. When this loop is complete and unbroken, a tiny flow called electric current moves around it, and the bulb glows. If there is even one tiny gap anywhere in the loop, the current cannot flow, and the bulb stays dark. This complete loop has a name: an electric circuit. A switch is simply a tool that lets us make or break that loop whenever we want.
Let’s Break It Down
What an electric circuit is, and its parts
An electric circuit is a complete path that lets electric current flow through it. Think of it as a closed loop, like a race track for the current.
Let us meet the parts that make up a simple circuit. Each one has a job.
1. The electric cell. A cell is a small store of electrical energy. It pushes the current around the circuit. Look at a torch cell. It has two ends, called terminals. One end has a small metal cap — this is the positive terminal, marked with a plus sign (+). The other end is a flat metal disc — this is the negative terminal, marked with a minus sign (−). The current leaves from the + end and returns to the − end.
2. The battery. Sometimes one cell is not enough. So we join two or more cells together in a line. This group of cells is called a battery. We will look at this more closely later.
3. The bulb (electric lamp). The bulb is the part that gives light. An old-style bulb has a very thin wire inside called the filament (a filament is just a thin coiled wire). When current flows through the filament, it gets very hot and glows, giving off light. Many torches now use an LED instead — a tiny lamp that gives light without a hot filament and uses much less energy.
4. The wires. Wires are the roads. They carry the current from one part to the next. They are usually made of a metal like copper, covered with a coat of plastic.
5. The switch. A switch lets you open or close the path. Press it one way and the bulb lights up. Press it the other way and the bulb goes off. We will see exactly how it does this soon.
A torch cell has a metal cap at one end and a flat disc at the other. Which one is the positive terminal?
The metal cap is the positive terminal (+). The flat metal disc is the negative terminal (−). Every cell has these two terminals, and the current flows out from the + cap.
A closed circuit vs an open circuit — why a bulb glows only when the path is complete
This is the most important idea in the whole chapter. So let us go slow.
Imagine a circle of children holding hands. They want to pass a ball around the circle, hand to hand. As long as everyone is holding hands, the ball can keep going around. But if just two children let go, there is a gap. The ball reaches that gap and stops. It cannot jump across.
Electric current is just like that ball. It can only move around if the path is complete with no gaps.
- A closed circuit is a complete loop with no gaps. The current flows all the way around, and the bulb glows.
- An open circuit has a gap somewhere. The current reaches the gap and stops. So no current flows, and the bulb stays off.
Now you can answer the torch question from the start. The torch lamp glows only when the circuit inside is closed (complete). When it is open (has a gap), the lamp stays dark. The switch is what makes the gap appear or disappear.
Here is why this happens, shown as a picture. Figure 3.1 below puts a closed circuit and an open circuit side by side.
So remember this rule: no complete path, no current, no light. The current does not leak out of the wires or jump across gaps. It only flows when the whole loop is joined up.
A circuit has a tiny break in one wire, but everything else is connected. Will the bulb glow?
No. Even one tiny gap anywhere in the loop breaks the path. The current cannot jump across the gap, so it stops, and the bulb stays off. The whole loop must be complete.
The switch — how it makes and breaks the path
A switch is a simple device that completes or breaks a circuit. That is its only job — but it is a very useful one. It lets us turn things on and off whenever we like, without pulling out wires every time.
How does it work? Inside a switch are two points that the current wants to pass between. A small movable part either touches both points or leaves a gap between them.
- When the moving part touches both points, the gap is closed. The path is complete. The circuit is closed (ON), and the bulb glows.
- When the moving part is lifted away, there is a gap between the points. The path is broken. The circuit is open (OFF), and the bulb goes dark.
You can build a switch yourself with two drawing pins, a safety pin, and a piece of cardboard. Pin down the safety pin at one end so it can swing. When you swing it across to touch the second pin, you close the gap and the bulb lights up. Swing it away, and the bulb turns off.
A switch can be placed anywhere in the circuit. It does not have to be next to the cell or the bulb. Wherever it sits, when it is OFF it makes a gap in the loop, and that is enough to stop the current everywhere.
Let us compare the two states clearly.
| What to look at | Closed circuit (switch ON) | Open circuit (switch OFF) |
|---|---|---|
| Is the path complete? | Yes, no gap | No, there is a gap |
| Does current flow? | Yes | No |
| Does the bulb glow? | Yes, it glows | No, it stays dark |
| Everyday example | Torch turned on | Torch turned off |
Circuit symbols and drawing a circuit diagram
Drawing a real cell, a real bulb, and curvy wires every time would take ages. So scientists agreed on simple symbols for each part. A drawing of a circuit made with these symbols is called a circuit diagram.
Figure 3.2 below is your chart of the standard symbols. Learn these — you will use them again and again.
Two things to notice in Figure 3.2. First, in the cell symbol the long line is the + terminal and the short line is the − terminal. Second, the bulb is a circle with a cross in it, and the open switch clearly shows a gap.
Now, how do we turn a real circuit into a clean diagram? We replace each real part with its symbol, and we draw the wires as straight lines that join everything into a loop. Figure 3.3 shows a real circuit becoming its circuit diagram.
Let us practise reading and drawing one.
A simple torch circuit has one cell, one bulb, and one switch that is turned ON, all joined in a single loop. Draw its circuit diagram using the correct symbols, and say whether the bulb glows.
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List the parts and pick the symbol for each. Cell → one long line (+) and one short line (−). Bulb → a circle with a cross inside. Switch ON → a line bridging two dots (no gap). Wires → straight lines.
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Arrange them in a loop. Draw a rectangle. Place the cell symbol on the bottom side, the bulb symbol on the top side, and the closed switch symbol on a side. Join all parts with straight wire lines so the loop has no break.
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Check the path. Start at the + (long line) of the cell, follow the wire through the switch and the bulb, and return to the − (short line) of the cell. The loop is complete, with no gap.
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Because the switch is ON, the circuit is closed and current flows all the way round. So the bulb glows. Your finished diagram looks like the diagram on the right side of Figure 3.3.
Conductors and insulators — testing materials
Why are wires made of metal and not, say, wood or plastic? Let us find out.
We can build a simple tool called a tester. Take a cell and a bulb joined by wires, but leave two wire ends free. Touch those two free ends to an object, one end on each side. If the bulb glows, current passed through the object. If the bulb stays dark, current did not pass.
Try this with many objects — a metal key, a coin, a plastic scale, a wooden block, a rubber eraser, a paper strip. You will find a clear pattern.
- For some materials, like a key or a coin, the bulb glows. Current flows through them easily. These are called conductors. A conductor is a material that lets electric current flow through it easily.
- For other materials, like plastic, wood, or rubber, the bulb stays off. Current cannot flow through them. These are called insulators. An insulator is a material that does not let electric current flow through it.
Figure 3.4 shows the tester at work on two materials.
Now the answer is clear. Metals are conductors, so wires are made of metal — usually copper, because it conducts well and is not too costly. And the plastic coat on the wire is an insulator, so it stops the current from leaking out and keeps you safe when you touch the wire.
Here is a quick side-by-side comparison.
| Aspect | Conductor | Insulator |
|---|---|---|
| Does current flow through it? | Yes, easily | No |
| Bulb in the tester | Glows | Stays off |
| Examples | Copper, iron, key, coin | Plastic, rubber, wood, glass |
| Used for | Making wires, switches | Covering wires, plug tops |
In the tester, you touch the two free ends to a wooden ruler and the bulb does not glow. Is wood a conductor or an insulator? Why?
Wood is an insulator. The bulb did not glow, which means current did not flow through the wood. Insulators block the current, so the path stays incomplete and the bulb stays off.
Cells and batteries — joining cells together
A single cell gives a certain push to the current. But many devices, like a torch, need more push or need to run for longer. So we join cells together to make a battery.
Here is the key rule for joining cells: the positive (+) terminal of one cell is connected to the negative (−) terminal of the next cell. We line them up plus-to-minus, plus-to-minus, in a row. Joining cells this way gives the circuit more energy and lets it run for a longer time.
Figure 3.5 shows a single cell, and then a battery made of three cells joined the right way.
If you open a torch and put the cells in the wrong way round, the lamp will not glow. That is why torches print small + and − marks inside the cell compartment — to show you which way each cell must point.
One small note: with an ordinary filament bulb, it does not matter which way you connect its two ends — it glows either way. But an LED is fussy. It only glows when its longer wire (the + side) connects toward the + side of the battery. Connect it the other way, and it stays dark. So LEDs must be put in the right way round.
When joining two cells into a battery, which terminal of one cell connects to which terminal of the next?
The positive (+) terminal of one cell connects to the negative (−) terminal of the next cell. We line them up plus-to-minus. This makes a working battery that gives more energy and lasts longer.
Common Mistakes
Let us clear up a few ideas that trip up many students. For each one, see why it feels right, then learn what is actually true.
A switch makes the electricity, like a small power source.
The switch is the thing you press to make the light come on, so it feels like the switch is what gives the light its power.
A switch does not make any electricity. The cell (or battery) is the source of energy. The switch only completes or breaks the path. When you press it ON, it closes the gap so current from the cell can flow; when OFF, it opens a gap and stops the flow.
If a wire is connected only to the positive terminal of the cell, the bulb will still glow.
The bulb is touching the cell through a wire, so it looks like it is properly connected and should light up.
One connection is not enough. The current needs a complete loop: out from the + terminal, through the bulb, and back to the − terminal. With only one terminal joined, there is no return path, the loop is open, and the bulb stays dark.
The plastic covering on a wire is what carries the electricity.
The plastic is the part you see and touch on the outside of the wire, so it seems like the important working part.
The plastic is an insulator — current cannot flow through it at all. The current actually flows through the metal (usually copper) inside. The plastic is only a safety coat that stops the current leaking out and protects you when you touch the wire.
Quick Check
Time to test yourself. Pick the best answer for each.
A bulb in a circuit does not glow. The cell and bulb both work fine. What is the most likely reason?
In the symbol for an electric cell, what does the LONG line stand for?
You test a rubber eraser with a tester and the bulb does not glow. The rubber is a:
Practice Problems
Easy
What is an electric circuit? Say it in one or two simple sentences.
An electric circuit is a complete path that lets electric current flow. It is made of parts like a cell, wires, a bulb and a switch joined in a loop. When the loop is complete, the bulb glows.
Name the two terminals of an electric cell and the sign used for each.
A cell has a positive terminal, marked with a plus sign (+), and a negative terminal, marked with a minus sign (−). On a torch cell, the metal cap is the + terminal and the flat disc is the − terminal.
Medium
A torch lamp glows when its switch is in one position but not in the other. Explain why, using the words 'open' and 'closed'.
When the switch is in the ON position, it closes the gap inside the circuit. The path becomes a complete loop — a closed circuit — so current flows from the cell through the lamp, and the lamp glows.
When the switch is in the OFF position, it leaves a gap in the path — an open circuit. The current cannot cross the gap, so no current flows and the lamp stays dark.
Why are electric wires made of copper but covered with plastic? Use the words 'conductor' and 'insulator'.
Copper is a conductor — it lets electric current flow through it easily — so it is used for the inner part that actually carries the current.
Plastic is an insulator — current cannot flow through it. The plastic coat stops the current from leaking out of the wire and protects anyone who touches the wire from a shock. So we need both: a conductor inside to carry the current, and an insulator outside for safety.
Challenge
Two cells are joined to make a battery, but a student connects the + terminal of one cell to the + terminal of the other. Will this work well as a battery? Explain how the cells should be joined.
No, this is the wrong way to join them. To build a proper battery, the positive (+) terminal of one cell must connect to the negative (−) terminal of the next cell — plus-to-minus, in a line.
Joining + to + does not line up the cells’ pushes correctly, so the battery will not give the steady extra energy we want. The correct plus-to-minus joining (shown in Figure 3.5) gives the circuit more energy and makes it last longer.
A circuit has a cell, a bulb and a switch. The switch is ON, but the bulb still does not glow. Give two possible reasons and how you would check each.
Even with the switch ON, the bulb may not glow for these reasons:
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A broken filament (fused bulb). The thin wire inside the bulb may be broken, leaving a gap inside the bulb itself. Check by swapping in a new bulb — if the new one glows, the old bulb was fused.
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A loose or broken wire connection. One of the wires may not be touching its terminal properly, making a hidden gap. Check each joint and press the wire ends firmly onto the terminals.
In both cases the real problem is the same: there is a gap somewhere, so the loop is not truly complete, and current cannot flow.
Summary
- An electric circuit is a complete path (a loop) that lets electric current flow. Its parts are the cell or battery, wires, a bulb, and a switch.
- An electric cell is a portable store of electrical energy. It has a positive (+) terminal (metal cap) and a negative (−) terminal (flat disc).
- A bulb glows only when the circuit is closed (a complete loop with no gap). In an open circuit there is a gap, current cannot flow, and the bulb stays dark.
- A switch is a simple device that completes (ON) or breaks (OFF) the circuit. It does not make electricity; it only opens or closes the path.
- Each part has a symbol. A drawing of a circuit using these symbols is a circuit diagram. In the cell symbol, the long line is + and the short line is −.
- Conductors (like metals) let current flow easily; insulators (like plastic, rubber, wood) do not. Wires use a metal conductor inside and a plastic insulator outside.
- A battery is two or more cells joined in a line, with the + terminal of one cell connected to the − terminal of the next.
- Stay safe: only experiment with torch cells and batteries. Never touch wall sockets, mains wires, or switches with wet hands — our body is a conductor, and mains electricity can be deadly.
What’s Next
You have seen that wires and keys are made of metals, because metals are good conductors of electricity. But what exactly makes a metal a metal? And how are metals different from materials like wood, plastic, or coal?
In the next chapter, The World of Metals and Non-metals, we will explore the special properties of metals — why they shine, why they can be hammered into shapes and drawn into wires — and meet the non-metals too. The conductor idea you learned here is your first clue into that world.
Frequently Asked Questions
What is an electric circuit and why does a bulb only glow when the circuit is complete?
An electric circuit is a complete, closed loop through which electric current can flow. A bulb glows only when the circuit is complete because current needs an unbroken path to move from one terminal of the cell, through the wires and bulb, and back to the other terminal. Even one tiny gap anywhere in the loop stops the current, so the bulb stays dark.
What is the difference between an open circuit and a closed circuit?
In a closed circuit the path for current is complete and unbroken, so current flows and the bulb lights up. In an open circuit there is a gap somewhere in the loop — often a switch that is off — so current cannot flow and the bulb does not light. A switch simply makes or breaks this path.
What are conductors and insulators and can you give examples?
A conductor is a material that allows electric current to pass through it easily. Most metals — copper, iron, aluminium — are good conductors, which is why wires are made of metal. An insulator does not allow current to pass through. Plastic, rubber, wood and glass are insulators, which is why wires are covered in plastic to keep you safe.
What is a battery and how is it different from a single cell?
A single cell is one small store of electrical energy with a positive (+) terminal and a negative (-) terminal. A battery is two or more cells joined together in a line to give a bigger push of electricity. A torch might use one cell, but a stronger device might need a battery of several cells.
Why do we use circuit diagrams with symbols instead of drawing real pictures?
Circuit diagrams use standard symbols (a short and long line for a cell, a cross in a circle for a bulb, two crossing lines for a switch) because they are quick, neat and understood by everyone everywhere. Drawing real pictures of every component would be slow and messy, and the pictures might look different depending on who draws them.