Lesson Notes By Weeks and Term v5 - Grade 12

Lesson Video

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Performance objectives

• Identify and explain the function of key components.
• Calculate total resistance in series and parallel circuits.
• Apply Ohm's Law to find voltage, current, and resistance.
• Construct and analyze simple circuits.
• Describe how a BJT transistor works as a switch.

Lesson summary

Electronic components are the building blocks of nearly all electronic devices we use every day, from our cell phones to traffic lights and renewable energy systems increasingly vital in South Africa. Understanding how these components function and how to connect them in basic circuits is crucial for anyone interested in electrical technology. South Africa, with its growing technology sector and focus on renewable energy, offers numerous opportunities for skilled individuals in this field. The principles learned in this topic will empower you to design, build, troubleshoot, and maintain electronic systems.

Lesson notes

2.1 Resistors Resistors are passive components that oppose the flow of electric current. Their resistance is measured in ohms (Ω). Resistors are used to limit current, divide voltage, and provide bias in electronic circuits.

Types: Fixed resistors, variable resistors (potentiometers and rheostats), thermistors, and light-dependent resistors (LDRs).

Color Code: Resistors are often marked with colored bands to indicate their resistance value and tolerance. Understanding the color code is essential for identifying the resistance. For example, a resistor with bands Brown, Black, Red, Gold has a resistance of 1, 0, x100 Ohms, +/-5% tolerance, therefore 1000 Ohms or 1k Ohms. 2.2 Capacitors Capacitors are passive components that store electrical energy in an electric field. Their capacitance is measured in farads (F). Capacitors are used for filtering, energy storage, and timing in electronic circuits.

Types: Electrolytic capacitors, ceramic capacitors, film capacitors. Electrolytic capacitors are polarized, meaning they have a positive and a negative terminal and must be connected with the correct polarity to avoid damage.

Capacitance: The capacitance of a capacitor depends on the area of the plates, the distance between the plates, and the dielectric material. 2.3 Inductors Inductors are passive components that store electrical energy in a magnetic field. Their inductance is measured in henries (H). Inductors are used for filtering, energy storage, and creating resonant circuits in electronic circuits.

Types: Air-core inductors, iron-core inductors, ferrite-core inductors.

Inductance: The inductance of an inductor depends on the number of turns of wire, the area of the coil, and the core material. 2.4 Diodes Diodes are semiconductor devices that allow current to flow in only one direction. They are used for rectification, switching, and voltage regulation.

Types: Rectifier diodes, Zener diodes, light-emitting diodes (LEDs).

Forward and Reverse Bias: A diode conducts when forward-biased (positive voltage applied to the anode, negative voltage to the cathode) and blocks current when reverse-biased. 2.5 Bipolar Junction Transistors (BJTs) BJTs are three-terminal semiconductor devices that can be used as amplifiers or switches.

They consist of three regions: emitter, base, and collector.

Types: NPN and PNP transistors.

Operation as a Switch: In a common-emitter configuration, a small current applied to the base can control a larger current flowing between the collector and emitter. This makes the BJT suitable for switching applications. Applying a sufficiently high voltage at the base (relative to the emitter) will "turn on" the transistor, allowing current to flow. Removing the base voltage "turns off" the transistor. Current Gain (β or hFE): The ratio of collector current (Ic) to base current (Ib) is called the current gain, denoted by β (beta) or hFE. 2.6 Ohm's Law Ohm's Law states the relationship between voltage (V), current (I), and resistance (R) in a circuit: V = I * R Where: V = Voltage (in volts) I = Current (in amperes) R = Resistance (in ohms) 2.7 Series and Parallel Circuits Series Circuits: Components are connected end-to-end, so the same current flows through each component. The total resistance (R_total) is the sum of the individual resistances: R_total = R1 + R2 + R3 + ...

Parallel Circuits: Components are connected side-by-side, so the voltage is the same across each component. The reciprocal of the total resistance is the sum of the reciprocals of the individual resistances: 1/R_total = 1/R1 + 1/R2 + 1/R3 + ...

Worked example

Example 1: Series Circuit

Three resistors are connected in series: R1 = 100 Ω, R2 = 220 Ω, and R3 = 330 Ω. If a 12V battery is connected across the series combination, what is the total resistance and the current flowing through the circuit?

Solution:

Total Resistance (R_total) = R1 + R2 + R3 = 100 Ω + 220 Ω + 330 Ω = 650 Ω

Current (I) = V / R_total = 12 V / 650 Ω = 0.0185 A or 18.5 mA

Example 2: Parallel Circuit

Two resistors are connected in parallel: R1 = 1 kΩ (1000 Ω) and R2 = 2 kΩ (2000 Ω). What is the total resistance of the parallel combination?

Solution:

1/R_total = 1/R1 + 1/R2 = 1/1000 Ω + 1/2000 Ω = 0.001 + 0.0005 = 0.0015

R_total = 1 / 0.0015 = 666.67 Ω