Lesson Notes By Weeks and Term v4 - SHS 2
CIRCUITS AND MACHINES
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CIRCUITS AND MACHINES
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Subject: Engineering
Class: SHS 2
Term: 2nd Term
Week: 11
Grade code: 2.2.1.LI.2
Strand code: 2
Sub-strand code: 1
Content standard code: 2.2.1.CS.1
Indicator code: 2.2.1.LI.2
Theme: ENERGY SYSTEMS
Subtheme: CIRCUITS AND MACHINES
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This lesson introduces the exciting world of electronic circuit design. We will move beyond just identifying components and learn how to combine them to create useful devices that solve real-world problems. In Ghana, from the automatic streetlights in our cities to the charger for your phone, or even the flashing lights on a "trotro", electronic circuits are everywhere. Understanding how to design them is a fundamental skill for any aspiring engineer, inventor, or technician. Today, we will focus on designing simple but important circuits like alarms, which can enhance safety and convenience in our homes and communities.
Before we can design a house, we must first understand the materials: bricks, cement, wood, and iron rods. Similarly, to design an electronic circuit, we must first understand our building blocks – the electronic components. A. Basic Electronic Components
| Component | Schematic Symbol | Function & Explanation | | :--- | :--- | :--- | | Resistor | | Function: To limit or resist the flow of electric current. Analogy: Think of it as a narrow pipe in a water system that reduces the flow of water. Resistors protect more sensitive components (like LEDs) from receiving too much current. Its value is measured in Ohms (Ω). | | Capacitor | | Function: To store electrical energy temporarily in an electric field. Analogy: It acts like a small, rechargeable battery that can charge and discharge very quickly. It is often used to smooth out variations in voltage. Its value is measured in Farads (F), but usually microfarads (μF). | | Light Emitting Diode (LED) | | Function: A type of diode that emits light when current flows through it in the correct direction. Analogy: A one-way street for electricity that lights up when traffic (current) is flowing. It has a positive terminal (anode) and a negative terminal (cathode). | | Buzzer | | Function: An output device that produces a sound (buzzing or beeping) when a voltage is applied across it. Analogy: An electric bell that tells you when the circuit is active. | | NPN Transistor (BJT) | | Function: A semiconductor device used for amplification or switching. We will use it as an electronic switch. It has three terminals: Base (B), Collector (C), and Emitter (E). | B. The Transistor as a Switch
The NPN transistor is the most important component for our alarm circuits. Think of it as an electronic tap. Collector (C): The main water inlet pipe. Emitter (E): The main water outlet pipe. Base (B): The handle of the tap.
How it works: OFF State: When there is no small current flowing into the Base (B), the tap is closed. No large current can flow from the Collector (C) to the Emitter (E). The circuit connected to the Collector is OFF. ON State: When a small current is applied to the Base (B), the tap opens. This allows a much larger current to flow from the Collector (C) to the Emitter (E). The circuit connected to the Collector is turned ON.