Lesson Notes By Weeks and Term v5 - Grade 10

Lesson Video

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Performance objectives

• Identify and draw symbols for 8 common components.
• Describe the function of each component.
• Explain the difference between fixed and variable resistors.
• Identify components in a simple circuit diagram.
• Explain the importance of fuses for household safety.

Lesson summary

In Electrical Technology, understanding basic components and their symbols is fundamental, like learning the alphabet before writing stories. These components are the building blocks of every electrical circuit, from the phone charger in your house to the traffic lights on Nelson Mandela Drive. Knowing what these components do and how they are represented allows you to read circuit diagrams, troubleshoot faults, and eventually design your own electrical circuits. This knowledge is crucial for future careers in fields like electrical engineering, electronics, and even automotive repair – all sectors that are vital to South Africa's economic growth and infrastructure development.

Lesson notes

Resistors: Definition: A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element. Resistors oppose the flow of electric current.

Symbol: The circuit symbol for a resistor is a zig-zag line ( ). In some older diagrams, a rectangle is used.

Function: Resistors limit current flow and create a voltage drop. The relationship between voltage (V), current (I), and resistance (R) is defined by Ohm's Law: V = I

R. Types: Fixed Resistors: Have a constant resistance value. They are commonly made from carbon composition, metal film, or wirewound materials. Variable Resistors (Potentiometers & Rheostats): Their resistance value can be adjusted. Potentiometers have three terminals and are used to control voltage (e.g., volume control in a radio). Rheostats have two terminals and are used to control current (e.g., dimmer switch for lights).

South African Context: Fixed resistors are used in almost all electronic devices, from cell phones to TVs. Variable resistors are used in appliances like ovens and geysers to control temperature. Dimmer switches in homes use rheostats. Street lights often use resistors to regulate current.

Capacitors: Definition: A capacitor is a passive two-terminal electrical component that stores electrical energy in an electric field.

Symbol: The circuit symbol for a capacitor is two parallel lines ( || ). There are slightly different symbols for polarized and non-polarized capacitors. A polarized capacitor symbol usually has a curved line indicating the negative terminal.

Function: Capacitors block DC current and allow AC current to pass. They store charge and release it when needed.

Types: Electrolytic Capacitors: Polarized, high capacitance, used for filtering and smoothing DC voltage.

Ceramic Capacitors: Non-polarized, low capacitance, used for high-frequency applications.

Film Capacitors: Non-polarized, various capacitance values, used for general-purpose applications.

South African Context: Capacitors are used in power supplies to smooth out voltage fluctuations, ensuring a stable power source for devices. They are also used in motor starters to provide the initial surge of current needed to start the motor.

Inductors: Definition: An inductor (also called a coil, choke, or reactor) is a passive two-terminal electrical component that stores energy in a magnetic field when electric current flows through it.

Symbol: The circuit symbol for an inductor is a coiled wire ( ). Sometimes, a dashed line is drawn above the coil to represent a core (e.g., ferrite core).

Function: Inductors resist changes in current. They store energy in a magnetic field and release it when the current decreases.

Types: Air-Core Inductors: Have no core.

Ferrite-Core Inductors: Have a ferrite core to increase inductance.

Iron-Core Inductors: Have an iron core for high inductance and current-carrying capacity.

South African Context: Inductors are used in power supplies, transformers, and filters. They are found in appliances like TVs, radios, and electric motors. Induction heating cookers use inductors.

Diodes: Definition: A diode is a semiconductor device that allows current to flow in only one direction.

Symbol: The circuit symbol for a diode is a triangle pointing towards a line ( ). The triangle represents the anode (+), and the line represents the cathode (-).

Function: Diodes rectify AC voltage to DC voltage. They also protect circuits from reverse voltage.

Types: Rectifier Diodes: Used for converting AC to D

C. Zener Diodes: Used for voltage regulation.

Light-Emitting Diodes (LEDs): Emit light when current flows through them.

South African Context: Diodes are used in power supplies, LED lighting, and solar panels. LEDs are increasingly used in traffic lights and streetlights due to their energy efficiency. Solar panels use diodes to prevent reverse current flow.

Light-Emitting Diodes (LEDs): Definition: A semiconductor light source that emits light when current flows through it.

Symbol: Similar to a diode, but with two arrows pointing away from the diode symbol to indicate light emission ( ).

Function: Converts electrical energy into light. They are much more energy-efficient than traditional incandescent bulbs.

South African Context: LEDs are replacing incandescent bulbs in homes and businesses across South Africa to reduce electricity consumption and costs. LED streetlights are also becoming increasingly common, contributing to safer and more energy-efficient communities. Traffic lights and vehicle lights now widely use LEDs.

Switches: Definition: A switch is an electrical component that can break an electrical circuit, interrupting the current or diverting it from one conductor to another.

Symbol: Various symbols depending on the type of switch. A simple SPST (Single Pole Single Throw) switch is represented by a line that can be connected or disconnected ( ).

Function: To control the flow of electricity in a circuit.