Lesson Notes By Weeks and Term v4 - SHS 2
ELECTROSTATICS
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ELECTROSTATICS
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Subject: Physics
Class: SHS 2
Term: 2nd Term
Week: 3
Grade code: 2.3.1.LI.4
Strand code: 3
Sub-strand code: 1
Content standard code: 2.3.1.CS.2
Indicator code: 2.3.1.LI.4
Theme: ELECTRIC FIELD, MAGNETIC FIELD AND ELECTRONICS
Subtheme: ELECTROSTATICS
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This lesson explores the fascinating and crucial role of capacitors, which are fundamental components in almost every electronic device we use. From the charger for your phone to the fan in the classroom and the sound system in a church or mosque, capacitors are working silently. Understanding how they behave when connected to different types of power sources – Direct Current (DC) like from a battery, and Alternating Current (AC) like from the ECG mains – is essential for any student of physics and technology. This knowledge helps us understand why our gadgets work the way they do and is a building block for more advanced electronics.
A. Quick Recap: What is a Capacitor?
A capacitor is an electronic component that stores electrical energy in an electric field. In its simplest form, it consists of two parallel conductive plates separated by an insulating material called a dielectric (e.g., air, paper, ceramic). Symbol: The circuit symbol for a capacitor is two parallel lines: `---| |---`
Its ability to store charge is measured in Farads (F). Since the Farad is a very large unit, we often use microfarads (μF, 10⁻⁶ F), nanofarads (nF, 10⁻⁹ F), or picofarads (pF, 10⁻¹² F). B. Behaviour of a Capacitor in a DC Circuit
A Direct Current (DC) source provides a constant voltage, and the current flows in only one direction. Think of a battery or a phone charger's output. The Charging Process: Imagine a simple circuit with a battery, a switch, a capacitor, and a small bulb. When the switch is closed, electrons from the negative terminal of the battery flow to the plate of the capacitor connected to it. This plate becomes negatively charged. These negative charges repel electrons from the opposite plate. These repelled electrons then flow towards the positive terminal of the battery. This leaves the second plate with a net positive charge. Initially, the current is at its maximum. This is because the capacitor is empty and offers no opposition. The bulb will light up brightly at first. As charge builds up on the plates, a potential difference (voltage) develops across the capacitor. This voltage opposes the voltage of the battery. As the capacitor's voltage increases, it pushes back harder against the current from the battery. Consequently, the flow of current decreases. The bulb will start to dim. The 'Steady State' or Fully Charged Condition: The capacitor continues to charge until the potential difference across it is equal to the potential difference of the DC source (the battery). At this point, the capacitor's voltage perfectly opposes the battery's voltage, and the current stops flowing completely. The bulb will go off. The capacitor is now "full" and will hold its charge as long as it is connected to the battery or isolated.