Lesson Notes By Weeks and Term v5 - Grade 10

Lesson Video

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Performance objectives

• Identify at least ten common electrical components and their symbols.
• Draw the circuit symbols for each component.
• Explain the basic function of each component.
• Differentiate between types of resistors and capacitors.
• Correctly interpret a simple circuit diagram.

Lesson summary

This week, we delve into the foundational elements of electrical circuits: basic electrical components and their corresponding circuit symbols. Understanding these components and symbols is absolutely crucial for any future electrician, technician, or engineer in South Africa. Just like knowing the alphabet is essential for reading and writing, recognising these components and symbols is essential for understanding and designing electrical circuits. Imagine trying to fix a broken radio in your community without knowing what a resistor or capacitor looks like, or how it's represented on a circuit diagram – it would be nearly impossible!

Lesson notes

Let's explore the essential building blocks of electrical circuits. We'll cover what they are, what they do, and how they're represented in circuit diagrams.

Resistors: A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element. Resistors are used to reduce current flow, adjust signal levels, divide voltages, bias active elements, and terminate transmission lines, among other uses.

Symbol: A resistor is typically represented by a zig-zag line (US standard) or a rectangle (European standard). Both are accepted, but consistency is key. We’ll use the zig-zag symbol here.

Function: Resistors resist the flow of electric current. The higher the resistance value (measured in Ohms, Ω), the more it resists the current.

Types: Fixed Resistors: Have a fixed resistance value. Variable Resistors (Potentiometers/Rheostats): The resistance can be adjusted. The symbol includes an arrow through the resistor symbol.

Thermistors: Resistance changes with temperature.

Colour Code: Resistors have coloured bands that indicate their resistance value. Understanding the colour code is crucial for identifying the resistance value without using a multimeter. Black = 0, Brown = 1, Red = 2, Orange = 3, Yellow = 4, Green = 5, Blue = 6, Violet = 7, Grey = 8, White =

9. Tolerance bands indicate the accuracy of the stated resistance value (e.g., Gold = 5%, Silver = 10%).

Example: A resistor has bands: Brown, Black, Red, Gold. Brown (1) Black (0) Red (2) means 10 x 10^2 = 1000 Ohms or 1 kΩ. Gold means +/- 5% tolerance.

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

Symbol: Two parallel lines (equal length).

Function: Capacitors store electrical energy. They block DC current and allow AC current to pass through. They are used for filtering, smoothing voltage, and storing energy.

Types: Electrolytic Capacitors: Polarized (have a positive and negative terminal). The symbol usually includes a curved line next to the straight line to indicate polarity (+). These are used for larger capacitance values.

Ceramic Capacitors: Non-polarized (no specific positive or negative terminal). These are used for smaller capacitance values.

Inductors (Coils): An inductor is a passive two-terminal electrical component that stores energy in a magnetic field when electric current flows through it. It opposes changes in current.

Symbol: A series of looped lines resembling a coil of wire.

Function: Inductors store energy in a magnetic field. They block AC current and allow DC current to pass through. They are used in filters, transformers, and oscillators.

Diodes: A diode is a two-terminal semiconductor device that conducts primarily in one direction (from anode to cathode).

Symbol: A triangle pointing to a line. The triangle represents the direction of current flow (conventional current - positive to negative).

Function: Diodes allow current to flow in one direction only. They are used for rectification (converting AC to DC), signal detection, and protecting circuits from reverse polarity.

Light Emitting Diode (LED): A special type of diode that emits light when current flows through it.

Symbol: Diode symbol with two arrows pointing away from it, indicating light emission.

Function: Emits light when forward biased.

Transistors: A semiconductor device used to amplify or switch electronic signals and electrical power.

Symbol: There are different symbols for different types of transistors (BJT, MOSFET). We will focus on the BJT (Bipolar Junction Transistor) NPN transistor.

Function: Transistors act as electronic switches or amplifiers.

Switches: A mechanical device used to make or break an electrical circuit.

Symbol: A line that can be moved to connect or disconnect from another line.

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

Fuses: A safety device containing a thin wire that melts and breaks the circuit if the current exceeds a certain level.

Symbol: A line inside a rectangle or a wavy line.

Function: To protect the circuit from overcurrent.

Transformers: A device that transfers electrical energy from one circuit to another through electromagnetic induction.

Symbol: Two sets of coiled lines (representing the primary and secondary windings) separated by two parallel lines (representing the core).

Function: To step up or step down voltage.

Batteries: A device that converts chemical energy into electrical energy.

Symbol: A long line and a short line, repeated. The long line represents the positive terminal.

Function: To provide a DC voltage source. Guided Practice (With Solutions)

Question 1: Identify the component represented by the following symbol: (Insert Zig-zag resistor symbol here) and describe its basic function.

Solution: The symbol represents a resistor. A resistor's basic function is to resist the flow of electric current.