Lesson Notes By Weeks and Term v4 - JHS 2
ELECTRICITY AND ELECTRONICS
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ELECTRICITY AND ELECTRONICS
Download the Lessonotes Mobile Ghana app for faster lesson access on Android and iPhone.
Subject: Science
Class: JHS 2
Term: 2nd Term
Week: 10
Grade code: B8.4.2.2.1
Strand code: 4
Sub-strand code: 2
Content standard code: B8.4.2.2
Indicator code: B8.4.2.2.1
Theme: FORCES AND ENERGY
Subtheme: ELECTRICITY AND ELECTRONICS
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In many devices learners use in Ghana—radios, mobile phone chargers, TV sets, torches, traffic lights, and even some solar systems—there are electronic parts that store electrical energy briefly and then release it when needed. One important component that does this is the capacitor. Understanding charging and discharging helps learners explain why an LED may glow then go off, why some devices keep working for a short time after switching off, and why circuits need resistors and diodes to protect components.
2.1 What is a Capacitor? A capacitor is an electronic component that stores electric charge (and electrical energy) for a short time and can release it later. It has two conducting plates separated by an insulator called a dielectric (plastic, ceramic, air, etc.). Unit of capacitance: farad (F) Common smaller units: microfarad: µF (1 µF = 0.000001 F) nanofarad: nF picofarad: pF
Capacitance (C) tells how much charge a capacitor can store per volt: \[ C = \frac{Q}{V} \] Where: \(C\) = capacitance (F) \(Q\) = charge stored (coulombs, C) \(V\) = voltage across capacitor (V)
Example (Ghana context): A small radio circuit may use a 100 µF capacitor to smooth the DC supply so the sound is stable (less humming).
2.2 Capacitor in a DC Circuit (What it does) In a DC circuit, a capacitor behaves in a special way: (A) During Charging When connected to a DC battery: At the start, the capacitor is uncharged, so it allows current to flow. As it charges, it stores more charge, and the voltage across it increases. The charging current gradually reduces. After a long time, it becomes “fully charged” and then acts like an open switch (almost no current flows).