Lesson Notes By Weeks and Term v5 - Grade 10

Lesson Video

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Performance objectives

• Identify and draw symbols for 10 common electrical components.
• Describe the function of each component.
• Interpret simple circuit diagrams.
• Differentiate between various types of resistors.

Lesson summary

Electricity powers our modern lives, from the lights in our homes and schools to the computers and cellphones we use every day. Understanding the fundamental components that make up electrical circuits and their corresponding symbols is crucial, not only for a career in electrical technology but also for understanding how the devices we use work. In South Africa, where access to reliable electricity is an ongoing challenge in some areas, knowing how basic circuits function can empower individuals to troubleshoot simple electrical problems and potentially contribute to sustainable energy solutions.

Lesson notes

2.1 Introduction to Electrical Components and Symbols Electrical circuits are made up of individual components, each performing a specific function. These components are represented in circuit diagrams using standardized symbols. Understanding these symbols is vital for interpreting and designing circuits. Think of these symbols as the alphabet of electrical engineering – you need to know them to "read" and "write" circuit diagrams. 2.2 Key Components and Their Symbols Here's a breakdown of essential components and their symbols, along with their functions: Resistor: Symbol: Zigzag line (see below) or a rectangle. ``` ____ / \ /______\ | | ------ OR ----- | | | | ----- ``` Function: Resistors impede the flow of current. They are used to control current levels, divide voltage, and provide resistance in circuits.

Types: Fixed Resistor: Has a constant resistance value. Colour bands indicate this value. Variable Resistor (Potentiometer/Rheostat): Allows the resistance to be adjusted. Used in volume controls, light dimmers, etc.

Light Dependent Resistor (LDR): Resistance changes with light intensity. Used in light sensors and automatic lighting systems.

Thermistor: Resistance changes with temperature. Used in temperature sensors and control systems.

Capacitor: Symbol: Two parallel lines of equal length (see below). Sometimes one side may be curved to indicate polarity (electrolytic capacitor). ``` | | | | --- ``` Function: Capacitors store electrical energy in an electric field. They are used for filtering, smoothing voltage, and timing circuits.

Inductor (Coil): Symbol: A coil of wire (see below). ``` ~~~~~~~~ ``` Function: Inductors store energy in a magnetic field. They are used in filters, transformers, and energy storage applications.

Diode: Symbol: Triangle pointing to a line (see below). Shows the direction of permitted current flow. ``` |>| -| |- --- ``` Function: Allows current to flow in only one direction. Used for rectification (converting AC to DC) and protection.

Light Emitting Diode (LED): Symbol: Diode symbol with two arrows pointing away from it (see below). ``` |>| -| |- --> --- --> ``` Function: Emits light when current flows through it in the forward direction. Used for indicator lights, displays, and lighting.

Switch: Symbol: A break in a circuit (see below). Several types (SPST, SPDT, DPST, DPDT) exist. ``` ---o o--- ``` Function: Opens or closes a circuit, controlling the flow of current.

Cell: Symbol: One short line and one long line (see below). ``` + ``` Function: Provides a single source of DC voltage.

Battery: Symbol: Multiple cells connected in series (see below). ``` - --- --- + + ``` Function: Provides a higher DC voltage than a single cell.

Fuse: Symbol: A line with a loop or a solid rectangle (see below). ``` ---/\/\--- OR ---[]--- ``` Function: A safety device that protects a circuit from overcurrent by melting and breaking the circuit.

Lamp (Light Bulb): Symbol: A circle with a cross inside (see below). ``` O / \ / \ \ / \ / O ``` Function: Converts electrical energy into light. 2.3 Worked Examples Example 1: Simple LED Circuit Imagine you want to light up an LED. LEDs are sensitive to current, so you need to use a resistor to limit the current and prevent damage. Draw a circuit diagram showing a battery, a resistor, and an LED connected in series. Indicate the direction of current flow.

Solution: ``` + ----/\/\----|>|---- - Resistor LED Battery ``` Explanation: The battery provides the voltage. The resistor limits the current to a safe level for the LED. The LED emits light when current flows from the positive terminal of the battery, through the resistor, through the LED (in the correct direction), and back to the negative terminal of the battery. The resistor is placed in series with the LE

D. Example 2: LDR-Controlled Lighting You want to design a system that automatically turns on a light when it gets dark using an LDR. Explain the basic concept, including the components involved and how they interact. A full circuit diagram is not required, but describe the necessary components and their connections.

Solution: The system needs an LDR, a resistor (fixed value), a transistor (used as a switch), a power source (battery or power supply), and a lamp. The LDR and the fixed resistor form a voltage divider circuit. As light levels decrease, the resistance of the LDR increases, causing the voltage at the base of the transistor to increase. When the voltage at the base of the transistor reaches a certain threshold, the transistor turns on, allowing current to flow through the lamp, and illuminating it. When light levels increase, the resistance of the LDR decreases, lowering the voltage at the base of the transistor. The transistor then turns off, switching off the lamp.

Example 3: Series Resistor Circuit Draw a circuit diagram showing three resistors connected in series with a 12V battery. The resistor values are 100 ohms, 220 ohms, and 330 ohms respectively.