Lesson Notes By Weeks and Term v5 - Grade 8

Lesson Video

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Performance objectives

• Identify components and draw circuit diagrams.
• Differentiate between series and parallel circuits.
• Explain how adding bulbs affects brightness in a series circuit.
• Understand the difference between open and closed circuits.

Lesson summary

Electricity powers our lives! From the lights in our homes and schools to the devices we use every day, electricity is crucial. In South Africa, access to reliable electricity is a significant issue affecting communities and the economy. Understanding how electricity works, and specifically how it flows in circuits, helps us to understand the technology around us, appreciate the importance of energy conservation, and even opens doors to careers in engineering, technology, and renewable energy. This week, we'll be focusing on the fundamentals of electric circuits.

Lesson notes

What is an Electric Circuit? An electric circuit is a complete, closed path through which electric current can flow. Think of it like a circular road for electricity. For electricity to flow, the circuit must be closed – meaning there are no breaks or gaps in the path. If there's a gap (an open circuit), the electricity can't flow, and the circuit won't work.

Components of a Circuit: Battery: The power source of the circuit. It provides the electrical energy that makes the current flow. The battery has a positive (+) and a negative (-) terminal. In circuit diagrams, a battery is represented by a long line and a short line, with the long line indicating the positive terminal. Sometimes multiple cells (batteries) are connected to make a larger battery.

Bulb (Lamp): A component that converts electrical energy into light energy. When current flows through the bulb, it lights up. In circuit diagrams, a bulb is represented by a circle with a cross inside, or a circle with a filament inside.

Switch: A device used to open or close the circuit. When the switch is closed, the circuit is complete, and current can flow. When the switch is open, the circuit is broken, and current stops flowing. In circuit diagrams, a switch is represented by a line that can be connected or disconnected.

Connecting Wires: Conductors (usually made of copper) that provide a path for the current to flow between the components. In circuit diagrams, connecting wires are represented by straight lines.

Circuit Diagrams: Circuit diagrams use standard symbols to represent the components in a circuit. This makes it easier to draw and understand circuits. Learning to draw and interpret these diagrams is crucial.

Types of Circuits: Series Circuit: In a series circuit, the components are connected one after the other along a single path. The current flows through each component in turn. If one component fails (e.g., a bulb burns out), the entire circuit breaks, and all the components stop working. Think of Christmas lights where if one bulb goes out, the whole string goes out.

Parallel Circuit: In a parallel circuit, the components are connected along multiple paths. The current can flow through each path independently. If one component fails, the other components continue to work because the current can still flow through the other paths. This is how most homes are wired – if one light blows, the others stay on. Current Flow in Series vs.

Parallel Circuits: Series: The current is the same at every point in a series circuit.

Parallel: The current splits at each junction (where the path divides) in a parallel circuit. The total current flowing into a junction is equal to the total current flowing out of the junction.

Bulb Brightness: Series: Adding more bulbs to a series circuit decreases the brightness of each bulb. This is because the battery has to share its energy amongst more bulbs, and each bulb receives less current.

Parallel: Adding more bulbs to a parallel circuit does not significantly affect the brightness of the other bulbs. Each bulb receives close to the full voltage of the battery.

Worked example

Example 1: Series Circuit with 2 Bulbs

Imagine you have a battery, two bulbs, and connecting wires. You connect them in a series circuit. What happens to the brightness of the bulbs if you add another bulb in series?

Solution:

When you add a third bulb in series, the total resistance of the circuit increases. Since the battery voltage remains the same, the current flowing through the circuit decreases (according to Ohm's Law, which you'll learn later, but the principle still applies). With less current flowing through each bulb, each bulb will be dimmer than before. The available energy is now shared between three bulbs instead of two.