Lesson Notes By Weeks and Term v5 - Grade 12

Lesson Video

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Performance objectives

• Identify and describe common electronic components.
• Analyze simple series and parallel DC circuits.
• Explain capacitor charging and discharging.
• Build and test simple circuits on a breadboard.
• Interpret basic circuit diagrams (schematics).

Lesson summary

This week, we delve into the heart of electronics: understanding electronic components and how they are used to build basic electronic circuits. This knowledge is crucial for anyone interested in electrical technology, whether you aspire to be an electrician, technician, engineer, or simply want to understand the technology that surrounds you every day. From the smartphones in our pockets to the traffic lights that keep our roads safe, electronic circuits are fundamental. In South Africa, with our growing emphasis on technology and innovation, understanding these circuits is essential for building a skilled workforce capable of maintaining, repairing, and developing new technologies.

Lesson notes

2.1 Resistors Resistors are passive components that oppose the flow of electric current. They are fundamental to controlling voltage and current levels in circuits. The resistance (R) is measured in ohms (Ω).

Ohm's Law: This fundamental law states the relationship between voltage (V), current (I), and resistance (R): `V = IR` or `I = V/R` or `R = V/I`.

Resistor Colour Codes: Resistors are often marked with colour bands to indicate their resistance value and tolerance. Learn to decode these bands using a colour code chart (Brown=1, Red=2, Orange=3, Yellow=4, Green=5, Blue=6, Violet=7, Grey=8, White=9, Black=0, Gold=5% tolerance, Silver=10% tolerance, No band=20% tolerance). The first two bands represent the first two digits of the resistance value, the third band is the multiplier (power of 10), and the fourth band indicates the tolerance.

Resistors in Series: The total resistance of resistors in series is the sum of their individual resistances: `R_total = R1 + R2 + R3 + ...` Resistors in Parallel: The reciprocal of the total resistance of resistors in parallel is equal to the sum of the reciprocals of their individual resistances: `1/R_total = 1/R1 + 1/R2 + 1/R3 + ...`. Alternatively, for two resistors: `R_total = (R1 R2) / (R1 + R2)` Example 1: A 100Ω resistor has colour bands Brown, Black, Brown, Gold.

Example 2 (Series): Three resistors, 100Ω, 220Ω, and 330Ω are connected in series. What is the total resistance? `R_total = 100Ω + 220Ω + 330Ω = 650Ω` Example 3 (Parallel): Two resistors, 100Ω and 200Ω are connected in parallel. What is the total resistance? `R_total = (100Ω * 200Ω) / (100Ω + 200Ω) = 20000Ω / 300Ω = 66.67Ω` 2.2 Capacitors Capacitors are passive components that store electrical energy in an electric field. They consist of two conductive plates separated by an insulating material (dielectric). The capacitance (C) is measured in farads (F).

Capacitance: `C = Q/V`, where Q is the charge stored and V is the voltage across the capacitor.

Capacitors in Series: `1/C_total = 1/C1 + 1/C2 + 1/C3 + ...` Capacitors in Parallel: `C_total = C1 + C2 + C3 + ...` Charging and Discharging: When a capacitor is connected to a voltage source, it charges up. The voltage across the capacitor increases exponentially over time. The rate of charging or discharging is determined by the time constant (τ). Time Constant (τ): For an RC circuit (a resistor and capacitor in series), the time constant is given by `τ = RC`, where R is the resistance in ohms and C is the capacitance in farads. After one time constant, the capacitor will be charged to approximately 63.2% of the applied voltage during charging, or discharged to 36.8% of its initial voltage during discharging.

Example 4: A 100µF capacitor is charged to 12

V. How much charge is stored? `Q = CV = (100 10^-6 F) 12V = 0.0012 Coulombs` Example 5: A 1kΩ resistor is connected in series with a 10µF capacitor. What is the time constant? `τ = RC = (1000Ω) (10 10^-6 F) = 0.01 seconds` 2.3 Inductors Inductors are passive components that store energy in a magnetic field when electric current flows through them. They consist of a coil of wire. The inductance (L) is measured in henries (H). We will not focus heavily on inductors this week, but their basic function should be understood. 2.4 Diodes Diodes are semiconductor devices that allow current to flow easily in one direction (forward bias) and block current flow in the opposite direction (reverse bias).

Forward Bias: When the anode (positive terminal) of the diode is more positive than the cathode (negative terminal), the diode conducts.

Reverse Bias: When the anode is more negative than the cathode, the diode does not conduct (ideally).

Voltage Drop: When a diode is forward biased, there is a small voltage drop across it (typically around 0.7V for silicon diodes).

Example 6: Consider a circuit with a 5V source, a 1kΩ resistor, and a diode connected in series. If the diode is forward biased, the voltage across the resistor will be approximately 5V - 0.7V = 4.3V. The current will be 4.3V/1kΩ = 4.3mA. If the diode is reverse biased, the current will be approximately 0A (assuming an ideal diode). 2.5 Transistors (NPN and PNP) Transistors are semiconductor devices that can act as switches or amplifiers.

They have three terminals: the base (B), the collector (C), and the emitter (E). We will focus on bipolar junction transistors (BJTs) – NPN and PNP types.

NPN Transistor: In an NPN transistor, a small current flowing from the base to the emitter controls a larger current flowing from the collector to the emitter. It turns ON when the base voltage is sufficiently higher (by about 0.7V) than the emitter voltage.

PNP Transistor: In a PNP transistor, a small current flowing from the emitter to the base controls a larger current flowing from the emitter to the collector. It turns ON when the base voltage is sufficiently lower (by about 0.7V) than the emitter voltage.