Lesson Notes By Weeks and Term v5 - Grade 7

Lesson Video

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Performance objectives

• Identify the basic components of a simple circuit.
• Draw a simple circuit diagram using standard symbols.
• Explain the function of each component.
• Differentiate between an open and a closed circuit.
• Construct a simple working circuit.

Lesson summary

Welcome to the exciting world of electrical systems! This week, we begin our journey into understanding basic circuits. Electricity is all around us, powering our homes, schools, and even our cell phones. From the lights that brighten our evenings to the appliances that make life easier, electricity plays a crucial role in our daily lives here in South Africa. Understanding how circuits work allows us to appreciate this technology and even troubleshoot simple electrical problems. Learning about circuits can even inspire some of you to become the electricians and engineers of tomorrow, helping to build and maintain the electrical infrastructure that our country needs.

Lesson notes

What is an Electrical Circuit? An electrical circuit is a complete path through which electricity can flow. Think of it like a water pipe system – for the water to flow, the pipe must be complete, with no breaks. Similarly, for electricity to flow, the circuit must be complete.

Basic Components of a Circuit: Power Source (Battery/Cell): This provides the energy to push the electricity around the circuit.

Batteries have two terminals: a positive (+) terminal and a negative (-) terminal. The voltage (measured in Volts, V) of the battery determines the amount of electrical "push". Imagine it as the pump in our water pipe analogy.

Conductors (Wires): These are typically made of copper because copper allows electricity to flow easily. They act as the "pipes" that carry the electricity from the power source to the other components and back. Wires are usually insulated with plastic to prevent shocks.

Load (Bulb/Resistor): This is the component that uses the electrical energy to do something, like produce light (in the case of a bulb) or heat (in the case of a heater). A resistor is a component that resists the flow of electricity, converting electrical energy into heat. The bulb is like the tap at the end of a pipe, it uses the water for some purpose.

Switch: This is a device that can open or close the circuit. When the switch is closed (ON), the circuit is complete, and electricity can flow. When the switch is open (OFF), the circuit is broken, and electricity cannot flow. The switch is like a valve on our water pipe, controlling the flow of water.

Circuit Diagrams: Instead of drawing pictures of the components, we use symbols to represent them in circuit diagrams. This makes it easier to understand and design circuits.

Here are the symbols we'll be using: Battery: A long line and a short line side-by-side (long line is the positive terminal, short line is negative). It's drawn as || Wire: A straight line. — Bulb: A circle with a cross inside. ⦵ Switch (Open): A line with a break in it. _/ \_ Switch (Closed): A straight line. — Open vs.

Closed Circuits: Closed Circuit: A complete circuit where electricity can flow continuously from the power source, through the components, and back to the power source. The bulb will light up.

Open Circuit: An incomplete circuit where there is a break in the path, preventing electricity from flowing. The bulb will not light up. This happens when a switch is open, or if a wire is disconnected.

Worked example

Example 1: Drawing a simple circuit with a battery, bulb and wires.

Identify Components: Battery, Bulb, Wires

Draw Battery: || (remembering long line is positive)

Draw Wires: Draw lines coming from each end of the battery symbol. —

Draw Bulb: Connect the wires to the bulb symbol ⦵. The lines coming from the battery connect to either side of the bulb.

Check: Is the circuit complete? Are all components connected by wires to form a loop?

Example 2: Drawing a circuit diagram of a battery, bulb, switch (open), and wires.

Identify Components: Battery, Bulb, Wires, Switch (open)

Draw Battery: ||

Draw Wires: —

Draw Switch (Open): _/ \_ Connect one end to a wire from the battery.

Draw Wires: — Connect the other end of the switch to the bulb.

Draw Bulb: ⦵ Connect the bulb back to the battery with a wire.

Example 3: Explaining the flow of electricity in a closed circuit.

In a closed circuit containing a battery, wires, and a bulb, electrons (tiny particles that carry electric charge) flow from the negative (-) terminal of the battery, through the wires, through the bulb (causing it to light up), and back to the positive (+) terminal of the battery. This continuous flow of electrons is what we call electric current.

Guided Practice (With Solutions)