Lesson Notes By Weeks and Term v3 - Senior Secondary 1
Electric circuits
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Electric circuits
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Subject: Basic Electronics
Class: Senior Secondary 1
Term: 2nd Term
Week: 3
Theme: Electronic Components And Circuits
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Explain the meaning of electric circuit. Identify types of circuit boards. Explain different circuit arrangements Calculate resistance in:i. Seriesii. Parallel, and iii. Series-parallel.
are connected in parallel. Calculate the total resistance.
Step 1: Identify the circuit type. This is a parallel circuit.
Step 2: Apply the parallel resistance formula. (Using the product-over-sum formula for two resistors simplifies it). $R_T = (R_1 \times R_2) / (R_1 + R_2)$ Step 3: Substitute values and calculate. $R_T = (6 \Omega \times 12 \Omega) / (6 \Omega + 12 \Omega)$ $R_T = 72 \Omega^2 / 18 \Omega$ $R_T = 4 \Omega$ Alternatively, using the reciprocal sum formula: $1/R_T = 1/R_1 + 1/R_2$ $1/R_T = 1/6 \Omega + 1/12 \Omega$ To add fractions, find a common denominator (12): $1/R_T = 2/12 \Omega + 1/12 \Omega$ $1/R_T = 3/12 \Omega$ $1/R_T = 1/4 \Omega$ $R_T = 4 \Omega$ The total resistance is $4 \Omega$.
Example 3: Series-Parallel Circuit Calculation Consider a circuit where $R_1 = 5 \Omega$ is in series with a parallel combination of $R_2 = 10 \Omega$ and $R_3 = 15 \Omega$. Calculate the total resistance.
Step 1: Identify and simplify the parallel section first. $R_{parallel} = (R_2 \times R_3) / (R_2 + R_3)$ $R_{parallel} = (10 \Omega \times 15 \Omega) / (10 \Omega + 15 \Omega)$ $R_{parallel} = 150 \Omega^2 / 25 \Omega$ $R_{parallel} = 6 \Omega$ Step 2: Redraw/re-conceptualize the circuit. Now, $R_1$ is in series with the equivalent resistance of the parallel combination ($R_{parallel}$). The circuit is effectively $R_1$ in series with $R_{parallel}$.
Step 3: Apply the series resistance formula. $R_T = R_1 + R_{parallel}$ $R_T = 5 \Omega + 6 \Omega$ $R_T = 11 \Omega$ The total resistance is $11 \Omega$. This section provides detailed explanations of core concepts related to electric circuits. 2.
1. Meaning of Electric Circuit An electric circuit is a closed, conductive path through which electric current can flow. For current to flow, the circuit must be complete (closed), have a power source, a load (or resistance), and connecting wires. If any part of the path is broken (an open circuit), current will cease to flow. Basic Components of a Simple Electric Circuit:
1. Power Source: Provides the electrical energy (voltage) to drive the current. Examples include batteries, power supplies, and generators.
2. Load/Resistor: A component that consumes electrical energy, converting it into another form (e.g., light in an LED, heat in a heater, mechanical motion in a motor). It provides resistance to the current flow.
3. Conducting Wires: Materials (typically copper) that provide a low-resistance path for electrons to flow from the power source to the load and back.
4. Switch (Optional but common): A device used to open or close the circuit, thereby controlling the flow of current to the load.
Diagram of a Simple Circuit: (Teacher should draw on the board)
Battery Symbol: Two parallel lines, one long (positive) and one short (negative).
Resistor Symbol: Zig-zag line.
Switch Symbol: A break in the wire with a pivot point.
Connecting Wires: Straight lines. 2.
2. Types of Circuit Boards Circuit boards are platforms used to physically connect and support electronic components.
1. Breadboard (Protoboard): Description: A reusable, solderless platform used for building temporary prototypes of electronic circuits. It typically consists of a plastic block with a grid of holes.
Internal Connections: Terminal Strips: The main area where components are placed. Holes are usually connected in vertical columns (e.g., 5 holes connected together) but broken in the middle to allow integrated circuits (ICs) to straddle the break.
Bus Strips (Power Rails): Located along the sides, these rows of holes are connected horizontally. They are typically used for power supply (VCC/positive) and ground (GND/negative) connections.
Advantages: No soldering required, making it easy to assemble and disassemble circuits. Components are reusable. Ideal for testing and experimenting with circuit designs quickly.
Disadvantages: Not suitable for permanent circuits. Can introduce parasitic capacitance/inductance, affecting high-frequency circuits. Connections can be loose, leading to unreliable performance.
Nigerian Context: Widely used in educational institutions and by hobbyists for learning electronics and rapid prototyping of small projects like simple LED flashers or sensor-based alarms.
2. Printed Circuit Board (PCB): Description: A board made of non-conductive material (e.g., fiberglass, epoxy resin) with conductive pathways (traces) etched or printed on its surface. Electronic components are mounted on the board and connected via these traces, usually by soldering.
Types: Single-sided: Conductive layer on one side.
Double-sided: Conductive layers on both sides.
Multi-layer: Multiple layers of conductive traces separated by insulating material.
Advantages: Highly reliable and durable connections (soldered). Compact and lightweight. Reproducible and suitable for mass production. Efficient heat dissipation for some designs.
Disadvantages: Difficult to modify or repair once fabricated. Requires specialized manufacturing processes. Higher initial cost for small quantities.
Nigerian Context: Found in almost all commercial electronic devices like mobile phones, televisions, radios, computers, and in industrial control systems. Technicians involved in repairing these devices often work with PCBs.
3. Veroboard (Stripboard): Description: A type of circuit board with parallel strips of copper tracks on one side and pre-drilled holes. Components are typically soldered to these tracks. Breaks in the tracks are made by drilling or cutting to create desired connections.
Advantages: More permanent than breadboards but less complex than PCBs. Good for small to medium-sized prototype circuits. Relatively easy to modify compared to PCBs.
Disadvantages: Prone to short circuits if tracks are not carefully cut. Can be more difficult to troubleshoot than breadboards. * Nigerian Context: Used by electronics enthusiasts and students for building semi-permanent projects when PCBs are too complex or expensive to produce. 2.
3. Different Circuit Arrangements Electronic components, particularly resistors, can be connected in various ways, or cutting to create desired connections.
Advantages: More permanent than breadboards but less complex than PCBs. Good for small to medium-sized prototype circuits. Relatively easy to modify compared to PCBs.
Disadvantages: Prone to short circuits if tracks are not carefully cut. Can be more difficult to troubleshoot than breadboards.
Nigerian Context: Used by electronics enthusiasts and students for building semi-permanent projects when PCBs are too complex or expensive to produce. 2.
3. Different Circuit Arrangements Electronic components, particularly resistors, can be connected in various ways, primarily series, parallel, or a combination of both. 2.3.
1. Series Circuit: Definition: In a series circuit, components are connected end-to-end, forming a single continuous path for current flow. The current has only one route to take.
Characteristics: Current: The current flowing through each component is the same. ($I_T = I_1 = I_2 = I_3 = ...$)
Voltage: The total voltage supplied by the source divides across the components. The sum of voltage drops across individual components equals the total source voltage. ($V_T = V_1 + V_2 + V_3 + ...$)
Resistance: The total (equivalent) resistance of the circuit is the sum of individual resistances. Formula for Total Resistance ($R_T$): $R_T = R_1 + R_2 + R_3 + ... + R_n$ Where $R_1, R_2, ... R_n$ are the individual resistances.
Example: Old-fashioned Christmas tree lights (where if one bulb blew, all went out). A simple torchlight where battery cells are connected in series. 2.3.
2. Parallel Circuit: Definition: In a parallel circuit, components are connected across the same two points, providing multiple alternative paths for current flow.
Characteristics: Voltage: The voltage across each component is the same as the total source voltage. ($V_T = V_1 = V_2 = V_3 = ...$)
Current: The total current supplied by the source divides among the parallel paths. The sum of currents through individual branches equals the total source current. ($I_T = I_1 + I_2 + I_3 + ...$)
Resistance: The reciprocal of the total (equivalent) resistance is the sum of the reciprocals of individual resistances. The total resistance is always less than the smallest individual resistance. Formula for Total Resistance ($R_T$): $1/R_T = 1/R_1 + 1/R_2 + 1/R_3 + ... + 1/R_n$ For two resistors in parallel: $R_T = (R_1 \times R_2) / (R_1 + R_2)$
Example: Household wiring (appliances are connected in parallel, allowing them to operate independently at the same voltage). Car headlights. 2.3.
3. Series-Parallel (Combination)
Circuit: Definition: A series-parallel circuit combines both series and parallel connections of components.
Method for Calculation: To calculate the total resistance, simplify the circuit by identifying and combining series and parallel sections step-by-step until the entire circuit is reduced to a single equivalent resistance.
1. First, simplify any purely parallel branches.
2. Then, combine these simplified branches with any series components.
3. Repeat until a single equivalent resistance is found. 2.
4. Calculating Resistance in Different Circuit Arrangements Example 1: Series Circuit Calculation Three resistors with values $R_1 = 10 \Omega$, $R_2 = 20 \Omega$, and $R_3 = 30 \Omega$ are connected in series. Calculate the total resistance.
Step 1: Identify the circuit type. This is a series circuit.
Step 2: Apply the series resistance formula. $R_T = R_1 + R_2 + R_3$ Step 3: Substitute values and calculate. $R_T = 10 \Omega + 20 \Omega + 30 \Omega$ $R_T = 60 \Omega$ The total resistance is $60 \Omega$.
Example 2: Parallel Circuit Calculation Two resistors with values $R_1 = 6 \Omega$ and $R_2 = 12 \Omega$ are connected in parallel. Calculate the total resistance.
Step 1: Identify the circuit type. This is a parallel circuit.
Step 2: Apply the parallel resistance formula. (Using the product-over-sum formula for two resistors simplifies it). $R_T = (R_1 \times R_2) / (R_1 + R_2)$ Step 3: Substitute values and calculate. $R_T = (6 \Omega \times 12 \Omega) / (6 \Omega + 12 \Omega)$ $R_T = 72 \Omega^2 / 18 \Omega$ $R_T = 4 \Omega$ Alternatively, using the reciprocal sum formula: $1/R_T = 1/R_1 + 1/R_2$ $1/R_T = 1/6 \Omega This section outlines the activities for both the teacher and the students to facilitate effective learning. 3.
1. Week 5: Day 1 - Introduction to Electric Circuits and Circuit Boards Teacher Activities: Introduction (10 min): Recall basic electrical concepts (current, voltage, resistance, Ohm's Law) from previous lessons.
Introduce the topic: "Electric Circuits." Ask students to name devices that use electricity, then ask how the internal parts are connected.
Explanation of Electric Circuit (15 min): Define an electric circuit clearly, emphasizing the need for a closed path. Draw and explain the basic components of a simple circuit (power source, load, wires, switch) on the whiteboard, using standard symbols.
Use an analogy: water flowing through pipes (pump=power source, narrow pipe=resistor, faucet=switch, full loop=closed circuit). Demonstration/Explanation of Circuit Boards (20 min): Show physical examples of a breadboard, a simple PCB (e.g., from an old radio/phone), and a Veroboard (if available). Pass them around for students to observe (carefully). Explain the features, internal connections, advantages, and disadvantages of each type of circuit board, linking them to their real-world uses in Nigeria. Demonstrate how to insert components into a breadboard and make simple connections.
Q&A (5 min): Address any immediate questions from students.
Student Activities: Participate in the recall session. Listen attentively and take notes on the definition of an electric circuit and its components. Observe and handle the different types of circuit boards, noting their physical characteristics. Ask clarifying questions about the functionality and uses of each board type. 3.
2. Week 5: Day 2 - Circuit Arrangements and Resistance Calculations Teacher Activities: Recap (5 min): Briefly review the definition of an electric circuit and the types of circuit boards.
Explanation of Series Circuits (15 min): Define series connection, drawing a clear circuit diagram with multiple resistors.
Explain the characteristics: same current, voltage division, sum of resistances. Derive the formula for total series resistance: $R_T = R_1 + R_2 + ...$ Work through Example 1 (Series Circuit Calculation) on the board, explaining each step.
Explanation of Parallel Circuits (20 min): Define parallel connection, drawing a clear circuit diagram.
Explain the characteristics: same voltage, current division, reciprocal sum for resistance. Derive the formula for total parallel resistance: $1/R_T = 1/R_1 + 1/R_2 + ...$ and the special case for two resistors. Work through Example 2 (Parallel Circuit Calculation) on the board, explaining each step. Explanation of Series-Parallel Circuits (15 min): Define combination circuits, drawing a sample diagram. Explain the step-by-step approach to simplify and calculate total resistance. Work through Example 3 (Series-Parallel Circuit Calculation) on the board, emphasizing breaking down complex problems into simpler parts. Practical Demonstration (15 min - if resources allow): Using a breadboard, power supply (e.g., 9V battery), resistors, and a multimeter: Wire a simple series circuit. Measure individual resistances and then the total resistance to confirm the formula. Wire a simple parallel circuit. Measure individual resistances and then the total resistance to confirm the formula. Safety
Note: Ensure low voltage/current for student safety.* Student Activities: Participate in the recap. Take detailed notes on series, parallel, and series-parallel circuit definitions, characteristics, and formulas. Copy the worked examples into their notebooks, understanding the step-by-step calculations. Observe the practical demonstration, noting how components are connected and measurements are taken. Attempt to draw the circuit diagrams in their notes as the teacher explains.
This topic has extensive real-life applications in the Nigerian context: Household Electrical Wiring and Appliance Repair: Application: Understanding why all household appliances (e.g., TV, fan, refrigerator) in a Nigerian home operate at the same voltage (230V) and can be turned on or off independently is due to parallel wiring. Conversely, students learn why a broken series connection (like a tripped fuse or circuit breaker) affects the entire circuit it protects. This knowledge is crucial for diagnosing simple electrical faults in homes and for the work of electricians in the community.
Integration: The teacher can discuss common household electrical issues (e.g., "why does my light stop working when I connect my kettle?") and relate them to series/parallel connections.
Electronics Repair and Local Technicians: Application: Local electronics repairers (e.g., phone repairers, radio/TV technicians in "computer villages" or local markets) frequently troubleshoot circuit boards (PCBs). Their ability to identify components and understand how they are interconnected (series, parallel, or combination) is vital for diagnosing faults and replacing defective parts.
Integration: Discuss the role of local technicians and how this knowledge forms the foundation of their trade. Encourage students to observe how these technicians work when they visit them.
Solar Power Systems and Battery Banks: Application: In Nigeria, with increasing reliance on solar power, understanding series and parallel connections is crucial for designing and installing solar panel arrays and battery banks. Solar panels are connected in series to increase voltage and in parallel to increase current capacity, tailored to meet specific power demands for homes or businesses. Batteries are also arranged similarly to achieve desired voltage and ampere-hour ratings.
Integration: Show images or diagrams of solar panel installations. Explain how series connections of panels contribute to charging batteries (increasing voltage) and how parallel connections help to power more devices (increasing current).