Lesson Notes By Weeks and Term v5 - Grade 12

Lesson Video

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Performance objectives

• Identify and describe the function of key components.
• Calculate total resistance in series and parallel.
• Analyze basic RC and RL circuits.
• Explain diode operation in a rectifier.
• Describe how a BJT works as a switch.

Lesson summary

This week, we delve into the fundamental building blocks of electronics: electronic components and basic circuits. Understanding these components and how they interact is crucial for anyone interested in electrical technology, whether you dream of designing the next groundbreaking gadget or simply maintaining the electrical systems that power our homes and industries. In South Africa, with its growing technological landscape and need for skilled technicians and engineers, a solid understanding of electronics offers significant opportunities for career advancement and entrepreneurship.

Lesson notes

2.1 Resistors: Resistors oppose the flow of electric current. The resistance (R) is measured in Ohms (Ω). The higher the resistance, the lower the current for a given voltage.

Types: Carbon composition, wire-wound, metal film, SM

D. Colour Code: Resistors typically use a colour code to indicate their resistance value and tolerance.

A typical resistor has 4 bands: Band 1: First digit Band 2: Second digit Band 3: Multiplier (power of 10)

Band 4: Tolerance (e.g., gold ±5%, silver ±10%)

Mnemonic: Black Brown Red Orange Yellow Green Blue Violet Grey White (0-9)

Example: A resistor with bands Brown, Black, Red, Gold: Brown (1), Black (0), Red (x10²) = 10 x 100 = 1000Ω = 1kΩ Gold = ±5% tolerance Series Resistors: Resistors connected in series add up.

The total resistance (R T ) is: R T = R 1 + R 2 + R 3 + ...

Parallel Resistors: The reciprocal of the total resistance is the sum of the reciprocals of individual resistances. 1/R T = 1/R 1 + 1/R 2 + 1/R 3 + ...

For two resistors in parallel: R T = (R 1 * R 2 ) / (R 1 + R 2 ) 2.2 Capacitors: Capacitors store electrical energy in an electric field. They consist of two conductive plates separated by an insulator (dielectric). The capacitance (C) is measured in Farads (F).

Types: Ceramic, electrolytic, film, tantalum.

Function: Blocking DC, passing AC, filtering, energy storage.

Capacitance Formula: C = Q/V, where Q is the charge and V is the voltage.

Units: Microfarad (µF = 10 -6 F), Nanofarad (nF = 10 -9 F), Picofarad (pF = 10 -12 F)

Markings: Capacitors often have their capacitance value and voltage rating printed on them. Electrolytic capacitors are polarised, meaning they have a positive and negative terminal. 2.3 Inductors: Inductors store energy in a magnetic field. They consist of a coil of wire. The inductance (L) is measured in Henries (H).

Types: Air core, iron core, ferrite core.

Function: Filtering, energy storage, creating magnetic fields.

Inductance Formula: V = L(di/dt), where V is the voltage, L is the inductance, and di/dt is the rate of change of current.

Units: Millihenry (mH = 10 -3 H), Microhenry (µH = 10 -6 H) 2.4 Diodes: Diodes allow current to flow in one direction only (ideally). They are made from semiconductor materials.

Types: Rectifier diodes, Zener diodes, LEDs.

Function: Rectification (converting AC to DC), voltage regulation, light emission.

Forward Bias: When the anode (+) is more positive than the cathode (-), the diode conducts.

Reverse Bias: When the anode is more negative than the cathode, the diode blocks current.

Forward Voltage Drop: A small voltage drop (typically 0.7V for silicon diodes) occurs across the diode when it is conducting. 2.5 Bipolar Junction Transistors (BJTs): BJTs are three-terminal devices that can amplify or switch electronic signals. They are made from semiconductor materials.

Types: NPN and PN

P. Terminals: Base (B), Collector (C), Emitter (E).

Function: Amplification, switching.

BJT as a Switch: A small current at the base can control a larger current flowing from the collector to the emitter (or emitter to collector for PNP). When the base current is sufficient, the transistor is "on" (saturated). When the base current is zero, the transistor is "off" (cut-off). 2.6 Ohm's Law: Ohm's Law states the relationship between voltage (V), current (I), and resistance (R): V = IR Where: V is the voltage in volts (V) I is the current in amperes (A) R is the resistance in ohms (Ω)