Lesson Notes By Weeks and Term v5 - Grade 7

Lesson Video

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Performance objectives

• Define the basic components of a circuit and their functions.
• Draw a simple circuit diagram using standard symbols.
• Explain the difference between an open and closed circuit.
• Build a simple working circuit.
• Explain the concept of current flow.

Lesson summary

Welcome, Grade 7 learners! This week, we dive into the fascinating world of electrical systems, specifically basic circuits. Understanding how electricity works is incredibly important. From charging your cell phones to powering the lights in your home and the traffic lights that keep our roads safe, electricity is essential to modern life in South Africa. Knowing the basics of circuits empowers you to understand, troubleshoot, and even build simple electrical devices. Imagine being able to fix a faulty Christmas light string or designing a small light-up project for a school exhibition!

Lesson notes

What is an Electrical Circuit? An electrical circuit is a complete path that allows electricity to flow from a power source to a component (like a light bulb) and back. Think of it like a closed loop water park slide. The water (electricity) needs a complete path to flow around. If there's a break in the slide (an open circuit), the water stops.

Basic Components of a Circuit: Power Source (Battery): The power source provides the energy that pushes the electricity around the circuit. It has a positive (+) and a negative (-) terminal. Batteries provide Direct Current (DC), meaning the electricity flows in one direction.

Think of a borehole pump: the pump provides the pressure to move the water (electricity).

Conductors (Wires): Conductors are materials that allow electricity to flow easily through them. Copper is the most common material used for wires because it's a good conductor and relatively inexpensive. Wires act like the pipes in our water park analogy, guiding the flow.

Load (Light Bulb/Resistor): The load is the part of the circuit that uses the electrical energy to do something. In our case, it will usually be a light bulb, converting electrical energy into light and heat. A resistor limits the amount of current flowing through the circuit. Imagine a water wheel; it uses the energy of the water to turn.

Switch: A switch is a device that opens or closes the circuit. When the switch is closed, the circuit is complete, and electricity can flow. When the switch is open, there's a break in the circuit, and the electricity stops flowing. The switch is like a gate on the water slide. Open vs.

Closed Circuits: Closed Circuit: A closed circuit is a complete path for electricity to flow. This means the switch is closed, and all components are connected. The light bulb will light up because electricity can flow through it.

Open Circuit: An open circuit has a break in the path, preventing electricity from flowing. This could be because the switch is open, a wire is disconnected, or the light bulb is blown. The light bulb will not light up.

Circuit Diagrams and Symbols: We use standard symbols to draw circuit diagrams, which are like maps of the circuit.

Here are some common symbols: Battery: A long line and a short line next to each other. The long line represents the positive (+) terminal, and the short line represents the negative (-) terminal. ( || )

Wire: A straight line. ( — )

Light Bulb: A circle with an "X" inside, or a circle with a filament shape inside. ( ⊙ ) or ( 💡)

Switch (Open): A broken line with a small circle on one side. ( –o )

Switch (Closed): A continuous line. ( — )

Resistor: A zig-zag line. ( ⩴ )

Current Flow: Electricity is the flow of electrons. Conventionally, we say that current flows from the positive (+) terminal of the battery, through the circuit components, and back to the negative (-) terminal. The more current flowing through a light bulb, the brighter it will be.

Worked example

Example 1: Draw a circuit diagram of a battery connected to a light bulb with a switch. The switch is closed.

Solution:

Battery (||) — Wire (—) — Switch (closed) (—) — Wire (—) — Light Bulb (⊙) — Wire (—) — Battery (||)

Example 2: Draw a circuit diagram of a battery connected to a light bulb with a switch. The switch is open.

Solution:

Battery (||) — Wire (—) — Switch (open) (–o ) — Wire (—) — Light Bulb (⊙) — Wire (—) — Battery (||)

Explanation: Notice the break in the line representing the open switch. This indicates that the circuit is incomplete.

Example 3: A circuit consists of a 1.5V battery, a switch, a light bulb, and connecting wires. When the switch is closed, the bulb lights up brightly. What happens if we add another light bulb in the circuit? Explain.