⚡ Electricity
Primary 5 Science — Summary Notes
Created by Miss Clarissa Ng · www.clartutors.com
1. Electric Circuits
- An electric circuit is made up of different parts that are connected together to allow current to flow through it.
- The different parts of an electric circuit are known as electrical components.
- A simple electric circuit consists of a battery, some wires, a bulb and a switch.
2. Parts of an Electric Circuit
| Component | What you need to know |
|---|---|
| Battery | The energy source of an electric circuit. It has a positive (+ve) terminal and a negative (−ve) terminal. When the positive terminal is connected to the negative terminal, the chemicals in the battery react to produce energy. |
| Wire | A wire is made of a thin strand of metal. The most common metal used to make wires is copper. Wires are used to connect electrical components to one another, to allow electric current to flow. Wires are usually insulated with a plastic/rubber covering. |
| Bulb | A light source. A bulb produces light and heat when electric current flows through it. A bulb is made up of different materials such as glass and metal. |
| Switch | Controls the flow of electric current in an electric circuit. If the switch is closed, electric current will flow. If the switch is open, no electric current will flow. |
3. Parts of a Bulb
A bulb is made up of the glass casing, metal filament, metal tip and metal casing.
The metal tip and metal casing must be properly connected to an electric circuit to light up a bulb.
4. Closed and Open Circuits
Closed circuit
Formed when all the electrical components in an electric circuit are connected without any gaps.
Open circuit
Formed when there is a gap between the electrical components in an electric circuit.
| In a closed circuit | In an open circuit |
|---|---|
| Electric current only flows in a closed circuit. | No electric current flows. |
| Electric current flows through and lights up the bulbs. | Electric current does not flow through and light up the bulbs. |
5. Electrical Conductors and Insulators
| Type | What you need to know |
|---|---|
| Electrical conductors | Materials that allow electric current to flow through them easily. Metals such as steel, copper and aluminium are electrical conductors. Some non-metals such as graphite (that pencil "lead" is made of) are also electrical conductors. |
| Electrical insulators | Materials that do not allow electric current to flow through them. Non-metals such as wood, glass, plastic and rubber are electrical insulators. |
To test whether an object is an electrical conductor or an electrical insulator, we can use a simple electric circuit:
- The object is placed between the two crocodile clips and the switch is closed.
- If the bulb lights up, the object is an electrical conductor.
- If the bulb does not light up, the object is an electrical insulator.
🧪 EXAM TIP
Explain both halves: an iron rod is a conductor of electricity, so a closed circuit is formed and current flows through the bulb, causing it to light up. A glass rod is a non-conductor, so an open circuit is formed, no current flows through the bulb, and the bulb does not light up.
6. Electrical Components and Their Symbols
| Component | Symbol | Function |
|---|---|---|
| Wire | Connects electrical components to one another. | |
| Battery | Energy source. Long line = positive (+ve) terminal · short thick line = negative (−ve) terminal |
|
| Light bulb | A light source. | |
| Switch in the 'off' position | Controls the flow of electric current (open circuit). | |
| Switch in the 'on' position | Controls the flow of electric current (closed circuit). |
7. Changing the Number of Batteries
- A battery is the energy source of an electric circuit.
- The larger the number of batteries connected in an electric circuit in series, the larger the amount of electric current flowing through the electric circuit.
- An increase in the number of batteries in series causes an increase in the brightness of the bulb.
Why a bulb becomes fused
If too many batteries are used, too much electric current will flow through the bulb and the metal filament will overheat and melt (fuse). A gap will form in the filament of the bulb. As a result, the bulb will become fused and will not light up.
8. Changing the Number of Bulbs
- The larger the number of bulbs connected in an electric circuit in series, the smaller the amount of electric current flowing through the electric circuit.
- An increase in the number of bulbs in series causes a decrease in the brightness of the bulbs.
9. Light Bulbs in Series
- When bulbs are arranged in series, current passes through each bulb in turn. There is only one pathway for current to flow.
- Hence, if one bulb fuses, there is a break in the circuit and the other bulbs will not light up.
- As the number of bulbs connected in series increases, the amount of current flowing through each bulb decreases. Therefore, the brightness of each bulb decreases.
10. Light Bulbs in Parallel
- When bulbs are arranged in parallel, there are separate pathways for current to flow. The current flows through a different pathway for each bulb.
- As the number of bulbs connected in parallel increases, the amount of current flowing through each bulb remains the same. Therefore, the brightness of each bulb remains the same.
Advantages
• Each bulb is brighter than when arranged in series.
• When one bulb fuses, the other bulbs remain lit.
• Each bulb can be controlled individually using switches.
Disadvantage
• The batteries in the circuit will be drained faster.
11. Summary — Series vs Parallel
| Series arrangement | Parallel arrangement | |
|---|---|---|
| Change in brightness when more bulbs are added | Each bulb in the circuit becomes dimmer. | The brightness of each bulb in the circuit remains the same. |
| Difference in the amount of current flowing through each bulb when more bulbs are added | The amount of current flowing through each bulb decreases. | The amount of current flowing through each bulb remains the same. |
| What happens when one bulb fuses | All bulbs do not light up. | Other bulbs remain lit. |
| Controlling bulbs | Bulbs cannot be controlled individually using switches. | Bulbs can be controlled individually using switches. |
| Battery life | Batteries will last longer. | Batteries will be drained faster. |
12. Safe Use of Electricity
- We must handle electricity with care because it can be very dangerous/hazardous.
- Electricity can cause a person to suffer an electric shock and fires to break out.
- Lives may be lost and properties may be destroyed by electric fires.
- To prevent electric fires, we should not overload a socket by putting too many plugs into it.
- We should also not use a plug or an appliance with exposed or damaged (frayed) wires.
13. Electromagnets
The magnetic strength of an electromagnet depends on:
| Factor | Effect |
|---|---|
| The amount of current passing through the wire | The greater the amount of current (e.g. by adding more batteries in series), the greater the magnetic strength of the electromagnet. |
| The number of coils of wire around the rod | The greater the number of coils of wire, the greater the magnetic strength of the electromagnet. |
14. The Electric Bell
- When the switch is pressed, a closed circuit is formed.
- Electric current flows through the circuit, causing the electromagnets to be magnetised.
- The electromagnets then attract the iron strip, causing the hammer to hit the gong and make a sound.
- At the same time, the metal contact no longer touches the iron strip, creating an open circuit.
- Electric current stops flowing through the electromagnets, causing them to lose their magnetism and stop attracting the iron strip.
- The iron strip then returns to its original position.
- A closed circuit is formed again, causing the hammer to hit the gong again.
⭐️ KEY POINT
The repetition of this process causes the alarm to ring — the bell works because making and breaking the circuit over and over makes the hammer strike the gong repeatedly.