Lesson Notes By Weeks and Term v5 - Grade 10

Lesson Video

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Performance objectives

• Identify and draw circuit symbols for common components.
• Describe the function of each component.
• Distinguish between different types of resistors, capacitors, and diodes.
• Interpret simple circuit diagrams.
• Apply Ohm's Law in basic calculations.

Lesson summary

This week, we delve into the fundamental building blocks of all electrical circuits: basic electrical components and their corresponding symbols. Understanding these components and their symbols is absolutely crucial for anyone working with electricity, from fixing a faulty appliance to designing complex electrical systems. Think about it – without knowing what a resistor or a capacitor does, or how to identify it in a circuit diagram, you're essentially trying to navigate a city without a map!

Lesson notes

Let's break down each component and its symbol, exploring its function and different types where applicable.

Resistors: Symbol: A zig-zag line (or a rectangle in some international standards). ``` Zig-zag: /\/\/\/\/ Rectangle: ------ | | ------ ``` Function: Resistors oppose the flow of electric current. They convert electrical energy into heat. The higher the resistance (measured in Ohms, denoted by Ω), the more it restricts current flow.

Types: Fixed Resistors: Have a specific, unchanging resistance value. Color codes indicate their resistance and tolerance. Learn to read resistor color codes; there are many online resources and apps to help. Variable Resistors (Potentiometers/Rheostats): Allow you to adjust the resistance. Used in volume controls, light dimmers, etc. Potentiometers have three terminals, while rheostats have two.

Light Dependent Resistors (LDRs): Their resistance changes with the amount of light falling on them. Used in automatic streetlights and light sensors. Resistance decreases with increasing light.

Thermistors: Their resistance changes with temperature. Used in temperature sensors and control systems.

There are two types: NTC (Negative Temperature Coefficient) – resistance decreases with increasing temperature, and PTC (Positive Temperature Coefficient) – resistance increases with increasing temperature.

Example 1: Calculating Voltage Drop Across a Resistor A circuit has a 12V battery connected to a 100Ω resistor. What is the voltage drop across the resistor?

Ohm's Law: V = IR (Voltage = Current x Resistance) First, find the current: I = V/R = 12V / 100Ω = 0.12A The voltage drop across the resistor is equal to the source voltage in a simple series circuit. Thus, the voltage drop is 12V. This is because all the voltage supplied by the battery is used by the resistor to restrict the current.

Capacitors: Symbol: Two parallel lines (equal length if non-polarized, curved line if polarized). ``` Non-polarized: | | Polarized: | ) ``` Function: Capacitors store electrical energy in an electric field. They block DC current and allow AC current to pass. Measured in Farads (F).

Types: Electrolytic Capacitors: Polarized (have a positive and negative terminal). Used for high capacitance values. Must be connected with correct polarity to avoid damage!

Ceramic Capacitors: Non-polarized. Used for lower capacitance values. More stable than electrolytic capacitors.

Example 2: Capacitor Function in a Circuit Imagine a simple circuit with a resistor and a capacitor in series, connected to a DC voltage source. Initially, the capacitor acts like a short circuit, allowing current to flow and charging up. As the capacitor charges, the current gradually decreases until the capacitor is fully charged, at which point it blocks further DC current flow.

Inductors: Symbol: A coil of wire. ``` ---/\/\/\--- ``` Function: Inductors store energy in a magnetic field when current flows through them. They oppose changes in current. Measured in Henries (H). Inductors are less common in basic circuits than resistors or capacitors at the Grade 10 level.

Types: Air-core, iron-core, ferrite-core. (Details beyond the scope of Grade 10 basic components)

Diodes: Symbol: A triangle pointing to a line. ``` |>| ``` Function: Diodes allow current to flow in only one direction. This is crucial for rectification (converting AC to DC).

Types: Signal Diodes: Used for low-current applications.

Rectifier Diodes: Used for high-current applications (power supplies).

Zener Diodes: Allow current to flow in the reverse direction when a specific voltage (the Zener voltage) is reached. Used for voltage regulation.

Light Emitting Diodes (LEDs): Emit light when current flows through them in the forward direction. They have a longer leg (anode - positive) and a shorter leg (cathode - negative). Important for energy-efficient lighting in South Africa.

Example 3: Diode in a simple circuit. A diode is connected in series with a resistor and a battery. If the diode is connected correctly (forward biased - anode to positive, cathode to negative), current will flow, and the resistor will limit the current. If the diode is connected in reverse (reverse biased), no current will flow (ideally).

Switches: Symbol: A break in a line with a pivoting arm. ``` SPST (Single Pole, Single Throw): ---o o--- (open) ---o---o--- (closed) SPDT (Single Pole, Double Throw): ---o o--- \ o--- ``` Function: Switches open or close a circuit, controlling the flow of current.

Types: SPST (Single Pole, Single Throw), SPDT (Single Pole, Double Throw), DPST (Double Pole, Single Throw), DPDT (Double Pole, Double Throw).

Fuses: Symbol: A line with a small break in the middle, often enclosed in a rectangle or circle. ``` ---//\--- or ---( )--- ``` Function: A safety device that protects circuits from overcurrent. It contains a thin wire that melts and breaks the circuit if the current exceeds a certain limit. Very important for preventing electrical fires.