Lesson Notes By Weeks and Term v3 - Senior Secondary 2
Capacitors
Download the Lessonotes Mobile Nigeria 2025 app for faster lesson access on Android and iPhone.
Capacitors
Download the Lessonotes Mobile Nigeria 2025 app for faster lesson access on Android and iPhone.
Subject: Radio Television And Repairs
Class: Senior Secondary 2
Term: 1st Term
Week: 1
Theme: Basic Electricity
This page supports the lesson note with a companion video and a short classroom-ready summary.
For class groups and homework, share this lesson page so learners also get the summary, objectives, and full lesson context.
Draw the graphic symbolfor fixed and variablecapacitors. Identify typesof capacitors. Usemultimeters to test capacitors.
where one set of plates (rotor) can be moved relative to another fixed set (stator). Air or plastic is often the dielectric.
Applications: Used in radio tuners (e.g., local radio stations in Nigeria use these for frequency selection), oscillator circuits.
Appearance: Often have a shaft for manual adjustment, typically metallic with air gaps or plastic between plates.
2. Trimmer Capacitors: Construction: Smaller versions of variable capacitors, often screw-adjusted.
Applications: Fine-tuning or calibration of circuits where small adjustments are needed. 2.
5. Graphic Symbols Students must be able to draw and identify these symbols: | Capacitor Type | Graphic Symbol | Description | | :------------------------------ | :------------------------------------------------- | :-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | Fixed Capacitor (Non-Polarized) |  | Two parallel lines of equal length. Used for ceramic, film, and mica capacitors. | | Fixed Capacitor (Polarized/Electrolytic) |  | One straight line (positive) and one curved line (negative), or a straight line and a shorter straight line with a "+" sign indicating the positive terminal. Used for electrolytic and tantalum capacitors. | | Variable Capacitor |  | Two parallel lines with an arrow passing diagonally through them, indicating adjustability. Used for tuning and trimmer capacitors. | 2.
6. Testing Capacitors with a Multimeter Safety Precaution: Always ensure the capacitor is fully discharged before testing, especially large electrolytic capacitors. This can be done by shorting its terminals with a resistor (e.g., 1kΩ) for a few seconds. High-value capacitors can store significant charge and deliver a dangerous shock.
A. Using a Digital Multimeter (DMM) with Capacitance Function: Many modern DMMs have a dedicated capacitance measurement range (indicated by 'F' or a capacitor symbol).
1. Discharge the Capacitor: Short the terminals as described above.
2. Select Capacitance Range: Turn the DMM dial to the capacitance function (e.g., μF, nF, pF).
3. Connect Probes: Connect the DMM probes to the capacitor terminals. Polarity matters for polarized capacitors if the DMM requires it, but generally, the DMM will measure irrespective of how the probes are connected to a non-polarized capacitor. For polarized capacitors, ensure the positive probe connects to the positive terminal and the negative probe to the negative terminal of the capacitor.
4. Read the Display: The DMM will display the capacitance value. Compare this value to the rating printed on the capacitor.
Good Capacitor: Reading is close to the marked value (within tolerance, e.g., ±10%, ±20%).
Open Capacitor: DMM shows "OL" (Over Limit) or 0 (depending on meter), indicating no capacitance.
Shorted Capacitor: DMM shows a very low resistance reading or a short circuit beep (if in resistance mode), or an extremely low/unstable capacitance reading.
B. Using an Analog Multimeter (VOM) in Resistance (Ohms)
Range: This method provides an indication of the capacitor's charging/discharging behavior, but not its precise capacitance value. It's effective for identifying shorted, open, or leaky capacitors.
1. Discharge the Capacitor: Crucial for electrolytic capacitors.
2. Select Resistance Range: Turn the VOM dial to a suitable resistance range (e.g., R x 1k or R x 10k for larger capacitors, R x 100 or R x 1 for smaller ones).
3. Zero the Meter: Short the probes together and adjust the "Zero Ohms" knob until the needle reads zero.
4. Connect Probes: For non-polarized capacitors: Connect probes to the terminals.
For electrolytic capacitors: Connect the red (positive) probe to the positive terminal and the black (negative) probe to the negative terminal.
5. Observe the Needle: Good Capacitor (Charging Sweep): The needle will momentarily deflect towards zero ohms (indicating low resistance as it charges) and then gradually move back towards infinity (indicating high resistance as it charges fully). The larger the capacitance, the slower the needle will return to infinity. For very small capacitors (pF/nF), the sweep might be too fast to observe.
Shorted Capacitor: The needle will deflect to zero ohms and stay there, indicating a short circuit.
Open Capacitor: The needle will not deflect at all, remaining at infinity, indicating an open circuit. * Leaky Capacitor: The needle will deflect but will not return fully to infinity; it will stop at some intermediate resistance value, indicating back towards infinity (indicating high resistance as it charges fully). The larger the capacitance, the slower the needle will return to infinity. For very small capacitors (pF/nF), the sweep might be too fast to observe.
Shorted Capacitor: The needle will deflect to zero ohms and stay there, indicating a short circuit.
Open Capacitor: The needle will not deflect at all, remaining at infinity, indicating an open circuit. * Leaky Capacitor: The needle will deflect but will not return fully to infinity; it will stop at some intermediate resistance value, indicating internal leakage.
6. Reverse Probes (Optional, for polarized): After the capacitor has fully charged and the needle is at infinity, reverse the probes. The needle should again sweep towards zero and return to infinity, indicating discharge and recharge in the opposite direction. 2.
1. Definition and Basic Principle A capacitor is a passive two-terminal electrical component designed to store electrical energy in an electric field. It essentially acts as a temporary battery, capable of charging and discharging. Its primary function is to store electric charge and electrical energy. 2.
2. Construction A basic capacitor consists of two conductive plates (usually metal) separated by an insulating material called a dielectric. The dielectric can be air, paper, mica, ceramic, plastic film, or an electrolytic solution. When a voltage is applied across the plates, an electric field is established in the dielectric, causing positive charge to accumulate on one plate and negative charge on the other. 2.
3. Capacitance Capacitance (C) is a measure of a capacitor's ability to store an electric charge. The higher the capacitance, the more charge it can store at a given voltage. The SI unit of capacitance is the Farad (F).
However, a Farad is a very large unit, so practical capacitors typically have capacitance values in: Microfarads (μF): 1 μF = 10−6 F Nanofarads (nF): 1 nF = 10−9 F Picofarads (pF): 1 pF = 10−12 F The capacitance value is determined by the area of the plates, the distance between them, and the type of dielectric material used. 2.
4. Types of Capacitors Capacitors are broadly classified into fixed and variable types. A. Fixed Capacitors (Most Common in Nigerian Electronics) These have a constant capacitance value that cannot be changed.
1. Electrolytic Capacitors: Construction: Consist of an anode (positive) of pure aluminum or tantalum, an electrolyte (ionic liquid or gel) acting as the cathode (negative), and an oxide layer on the anode surface acting as the dielectric.
Polarity: They are polarized, meaning they must be connected correctly with respect to the voltage polarity (positive to positive, negative to negative). Incorrect connection can lead to overheating, bulging, or even explosion, a common issue in power supplies of old televisions and radios. The negative terminal is usually marked with a stripe or a shorter lead.
Capacitance Range: High capacitance values (typically from 0.1 μF up to thousands of μF).
Applications: Commonly used for power supply filtering (smoothing out pulsating DC voltage from rectifiers in TVs, radios, chargers), coupling, and decoupling applications.
Appearance: Cylindrical shape, often larger than other fixed types, with capacitance and voltage ratings clearly printed.
2. Ceramic Capacitors: Construction: Use ceramic material as the dielectric.
Polarity: Non-polarized, meaning they can be connected in any orientation in AC or DC circuits.
Capacitance Range: Small capacitance values (typically pF to low μF).
Applications: High-frequency coupling and decoupling, timing circuits, resonant circuits, often found in RF sections of radios and digital logic circuits.
Appearance: Small, disc-shaped or rectangular, often blue, brown, or orange. Markings (e.g., 104 for 0.1 μF) use a code system.
3. Film Capacitors (e.g., Polyester, Polypropylene): Construction: Use thin plastic films (polyester, polypropylene, Mylar) as the dielectric.
Polarity: Non-polarized.
Capacitance Range: Medium capacitance values (nF to low μF).
Applications: Timing circuits, audio coupling, precision applications where stability is important. Common in audio amplifiers and certain power supply sections.
Appearance: Rectangular or oval shape, often green, red, or yellow, with clear markings.
4. Mica Capacitors: Construction: Use mica as the dielectric.
Polarity: Non-polarized.
Capacitance Range: Small (pF).
Applications: High precision, high frequency, and high-temperature applications. Often found in RF transmitters and filters.
Appearance: Often flat, rectangular, brownish, or silvery. B. Variable Capacitors These capacitors allow their capacitance value to be manually adjusted.
1. Tuning Capacitors: Construction: Typically multi-plate capacitors where one set of plates (rotor) can be moved relative to another fixed set (stator). Air or plastic is often the dielectric.
Applications: Used in radio tuners (e.g., local radio stations in Nigeria use these for frequency selection), oscillator circuits.
Appearance: Often have a shaft for manual adjustment, typically metallic with air gaps or plastic between plates.
2. Trimmer Capacitors: Construction: Smaller versions of variable capacitors, often screw-adjusted.
Applications: Fine-tuning or calibration of circuits where small adjustments are needed. 2.
5. Graphic Symbols Students must be able to draw 3.
1. Teacher Activities Introduction & Review: Begin by reviewing basic electricity concepts, especially charge, voltage, and current, and introduce capacitors as components that store charge.
Conceptual Explanation: Explain what a capacitor is, its basic construction (plates, dielectric), and the concept of capacitance. Use an analogy, like a water tank (capacitor) storing water (charge).
Types of Capacitors Presentation: Present physical samples or high-quality images of various fixed capacitors (electrolytic, ceramic, film) and variable capacitors (tuning, trimmer).
Highlight key features: physical size, markings (capacitance, voltage, polarity), typical appearance. Discuss typical applications relevant to Nigerian contexts (e.g., electrolytic in TV power supplies, ceramic in radio tuners).
Symbol Demonstration: Draw the graphic symbols for fixed (non-polarized), fixed (polarized/electrolytic), and variable capacitors clearly on the board. Explain the significance of each part of the symbol, especially the polarity marking. Multimeter Testing Demonstration (Practical Session): Safety First: Emphasize and demonstrate how to safely discharge capacitors before testing.
Digital Multimeter: Demonstrate how to select the capacitance range, connect probes, and interpret readings for a known good, shorted, and open capacitor (if available).
Analog Multimeter: Demonstrate how to select a suitable resistance range, zero the meter, connect probes, and observe the needle's "sweep" for good, shorted, open, and leaky capacitors. Explain the difference in sweep time for different capacitance values. Use a variety of capacitors (small ceramic, medium film, large electrolytic) to show different responses. 3.
2. Student Activities Brainstorming & Discussion: Students will be asked to identify where they might have seen components resembling capacitors in common Nigerian electronic devices (e.g., old radio, TV, fan, charger).
Observation & Identification: Students will observe and handle various types of capacitors provided by the teacher, identifying them by type, noting their markings (capacitance, voltage, polarity), and discussing their likely uses.
Symbol Drawing: Students will practice drawing the graphic symbols for fixed (non-polarized), fixed (polarized), and variable capacitors in their notebooks.
Multimeter Practice: Under strict teacher supervision, students will work in groups to: Practice safely discharging various capacitors. Use a digital multimeter (if available) to measure capacitance values of several known capacitors. Use an analog multimeter to test the same capacitors, observing the needle's behavior and classifying them as good, open, shorted, or leaky. Record their observations and compare with expected results.
Q&A and Problem Solving: Engage in questions and answers to clarify concepts and reinforce understanding of capacitor types, symbols, and testing procedures.
Power Supply Filtering in Home Appliances: Capacitors, especially large electrolytic ones, are indispensable in the power supply units of almost every electronic device in Nigerian homes – televisions, radios, DVD players, fan regulators, and phone chargers. They smooth out the pulsating DC voltage produced by rectifiers, ensuring a stable and clean power supply to sensitive electronic components. Without them, devices would experience humming (in audio), flickering (in video), or erratic operation.
Radio Tuning and Selection: Variable capacitors are at the heart of analogue radio receivers prevalent in many Nigerian households, especially in rural areas. By adjusting the knob of a radio, the variable capacitor changes its capacitance, which in turn changes the resonant frequency of the tuning circuit, allowing the listener to select different local radio stations like Wazobia FM, Bond FM, or BBC Hausa, etc.
Timing and Control Circuits: Capacitors are used in conjunction with resistors (RC circuits) to create time delays. This principle is applied in various devices: Fan Regulators: Some older fan regulators use RC circuits to control fan speed.
Traffic Lights: The timing sequence of traffic lights (e.g., at busy junctions in Lagos or Abuja) can be controlled by circuits utilizing capacitors.
Car Indicators/Blinkers: The rhythmic blinking of car indicator lights or hazard lights relies on RC timing circuits.