Activity: To identify a diode, an LED, a resistor and a capacitor from a mixed collection of such items
Introduction
This worksheet is designed to help you identify and understand the basic electronic components commonly used in circuits. By the end of this activity, you will be able to visually identify diodes, LEDs, resistors, and capacitors, understand their functions, and recognize their schematic symbols.
Electronic components are the building blocks of any electronic circuit. Being able to identify them correctly is a fundamental skill in electronics. This worksheet covers four essential components:
- Diodes - Allow current to flow in one direction only
- LEDs (Light Emitting Diodes) - Special diodes that emit light when current flows
- Resistors - Limit the flow of electric current
- Capacitors - Store and release electrical energy
Materials Required
- Assorted electronic components (diodes, LEDs, resistors, capacitors)
- Multimeter
- Magnifying glass (optional)
- Battery (3-9V)
- Breadboard
- Connecting wires
- 470Ω resistor (for LED testing)
Component Identification Guide
1. Diodes
Physical Appearance:
- Small cylindrical components with a band marking on one end
- Usually black, glass, or colored body
- Two leads (terminals)
- The band indicates the cathode (negative) end
Function:
Diodes allow current to flow in one direction only (from anode to cathode) and block it in the reverse direction. This rectifying property makes them useful in:
- Converting AC to DC (rectification)
- Protection circuits
- Logic gates
- Signal demodulation
The ideal diode equation is given by:
$I = I_S \left( e^{\frac{V_D}{nV_T}} - 1 \right)$
Where:
- $I$ is the diode current
- $I_S$ is the reverse saturation current
- $V_D$ is the voltage across the diode
- $n$ is the ideality factor
- $V_T$ is the thermal voltage ($\approx 26$ mV at room temperature)
Error loading equation. Please refresh the page.
Schematic Symbol:
How to Test:
- Set multimeter to diode test mode (diode symbol)
- Connect the red probe to the anode (unmarked end) and black probe to cathode (banded end)
- A reading between 0.5V to 0.7V indicates a functioning silicon diode
- Reverse the probes - you should see "OL" (overload) indicating no current flow
2. LEDs (Light Emitting Diodes)
Physical Appearance:
- Round or rectangular plastic enclosure (usually colored)
- Two leads of different lengths
- The longer lead is the anode (positive)
- The shorter lead is the cathode (negative)
- The casing may have a flat edge on the cathode side
Function:
LEDs are special diodes that emit light when current flows through them. They are widely used in:
- Indicators and displays
- Lighting fixtures
- Remote controls (infrared LEDs)
- Optical communication
The wavelength of light emitted by an LED is related to the bandgap energy:
$\lambda = \frac{hc}{E_g}$
Where:
- $\lambda$ is the wavelength of the emitted light
- $h$ is Planck's constant ($6.626 \times 10^{-34}$ J·s)
- $c$ is the speed of light ($3 \times 10^8$ m/s)
- $E_g$ is the bandgap energy of the semiconductor
Error loading equation. Please refresh the page.
Schematic Symbol:
How to Test:
- Connect a 470Ω resistor in series with the LED
- Connect the longer lead (anode) to the positive terminal of a battery through the resistor
- Connect the shorter lead (cathode) to the negative terminal
- If the LED lights up, it's functioning correctly
- Never connect an LED directly to a battery without a current-limiting resistor!
| LED Color | Typical Forward Voltage | Wavelength Range |
|---|---|---|
| Red | 1.8-2.2V | 620-750 nm |
| Green | 2.0-3.0V | 495-570 nm |
| Blue | 2.7-3.3V | 450-495 nm |
| White | 3.0-3.6V | Broad spectrum |
3. Resistors
Physical Appearance:
- Small cylindrical components with colored bands
- Two leads (terminals), one at each end
- No polarity (can be connected either way)
- Color bands indicate resistance value and tolerance
Function:
Resistors limit the flow of electric current and are used for:
- Current limiting
- Voltage division
- Biasing active components
- Timing circuits
Ohm's Law defines the relationship between voltage, current, and resistance:
$V = I \times R$
Where:
- $V$ is voltage in volts (V)
- $I$ is current in amperes (A)
- $R$ is resistance in ohms (Ω)
Error loading equation. Please refresh the page.
Resistor Color Code:
| Color | 1st & 2nd Band | Multiplier | Tolerance |
|---|---|---|---|
| Black | 0 | 10⁰ | - |
| Brown | 1 | 10¹ | ±1% |
| Red | 2 | 10² | ±2% |
| Orange | 3 | 10³ | - |
| Yellow | 4 | 10⁴ | - |
| Green | 5 | 10⁵ | ±0.5% |
| Blue | 6 | 10⁶ | ±0.25% |
| Violet | 7 | 10⁷ | ±0.1% |
| Grey | 8 | 10⁸ | ±0.05% |
| White | 9 | 10⁹ | - |
| Gold | - | 10⁻¹ | ±5% |
| Silver | - | 10⁻² | ±10% |
How to Read Resistor Values:
For a 4-band resistor:
- First band: First digit
- Second band: Second digit
- Third band: Multiplier
- Fourth band: Tolerance
Example: A resistor with bands Red-Violet-Orange-Gold has a value of 27 × 10³ Ω = 27 kΩ with ±5% tolerance.
Schematic Symbol:
How to Test:
- Set multimeter to resistance mode (Ω)
- Connect the probes to both ends of the resistor (polarity doesn't matter)
- Read the value and compare with the color code calculation
4. Capacitors
Physical Appearance:
Capacitors come in many forms:
- Electrolytic: Cylindrical with markings, polarized (negative terminal marked)
- Ceramic: Small disk-shaped or rectangular components
- Film: Box-shaped with markings for value
- Tantalum: Drop-shaped with marking for polarity
Function:
Capacitors store and release electrical energy and are used for:
- Filtering (smoothing) power supplies
- Decoupling (bypassing) signals
- Timing circuits
- Coupling AC signals between circuit stages
- Energy storage
The capacitance formula:
$C = \frac{Q}{V}$
Where:
- $C$ is capacitance in farads (F)
- $Q$ is electric charge in coulombs (C)
- $V$ is voltage in volts (V)
Error loading equation. Please refresh the page.
The energy stored in a capacitor:
$E = \frac{1}{2}CV^2$
Error loading equation. Please refresh the page.
Types of Capacitors:
| Type | Typical Range | Polarized | Common Uses |
|---|---|---|---|
| Ceramic | 1 pF - 1 µF | No | High-frequency filtering, decoupling |
| Film | 1 nF - 10 µF | No | Precision timing, signal coupling |
| Electrolytic | 1 µF - 10,000 µF | Yes | Power filtering, bulk storage |
| Tantalum | 0.1 µF - 100 µF | Yes | Compact filtering, stable timing |
Capacitor Markings:
Capacitors may be marked in several ways:
- Direct value (e.g., 10µF)
- Code (e.g., 104 = 10 × 10⁴ pF = 100 nF)
- Polarity marking on electrolytic capacitors (- symbol or band)
Schematic Symbol:
Non-polarized capacitor
Polarized capacitor
How to Test:
- Discharge the capacitor by connecting a resistor across its terminals
- For electrolytic capacitors, set multimeter to capacitance mode
- Connect red probe to positive and black to negative terminal
- Read the value and compare with the marking
- Alternatively, for basic testing:
- Set multimeter to resistance mode (high range)
- Connect to capacitor terminals
- Observe resistance rising (charging) then approaching infinity
Activity Tasks
Task 1: Component Sorting
- From the mixed collection of components, separate them into four groups: diodes, LEDs, resistors, and capacitors.
- In your lab notebook, sketch each type and list the visual characteristics that helped you identify them.
Task 2: Resistor Values
- Select three different resistors from your sorted pile.
- Use the color code chart to determine their values.
- Verify these values using a multimeter set to resistance mode.
- Record both the calculated and measured values in a table.
Task 3: Testing Diodes and LEDs
- Using a multimeter in diode test mode, determine the anode and cathode of each diode and LED.
- Build a simple circuit on a breadboard to light up an LED (use a 470Ω resistor in series).
- Verify the diode's one-way conduction by inserting it in a simple battery circuit in both forward and reverse directions. Record your observations.
Task 4: Capacitor Identification
- Identify which capacitors are polarized and which are non-polarized.
- Determine the capacitance values from their markings.
- If your multimeter has a capacitance function, measure and compare the actual values with the markings.
Application Questions
- Why would you choose to use an LED instead of a regular diode in a circuit?
- In what situations would you need to be careful about the polarity of a capacitor?
- Calculate the current flow through a 220Ω resistor when connected to a 9V battery using Ohm's Law.
- Why are resistors often used in series with LEDs?
- Design a simple circuit using at least one of each component (diode, LED, resistor, and capacitor). Explain the function of your circuit.
Circuit Design Challenge
Using the components you've identified, design and build a simple flashing LED circuit on a breadboard. Your circuit should include:
- At least one LED
- Appropriate resistors
- At least one capacitor
- A power source
For a basic RC timing circuit, the time constant is given by:
$\tau = R \times C$
Where:
- $\tau$ is the time constant in seconds
- $R$ is resistance in ohms
- $C$ is capacitance in farads
Error loading equation. Please refresh the page.
Safety Precautions
- Always discharge capacitors before handling them, as they can store charge even when disconnected from a power source.
- Never connect LEDs directly to a power source without a current-limiting resistor.
- Be careful when handling small components to avoid losing them.
- Electrolytic capacitors can explode if connected with incorrect polarity or if exposed to voltages higher than their rating.
- Ensure your work area is clean and organized to prevent short circuits.
Assessment
You will be assessed on the following criteria:
- Correct identification of all components (25%)
- Accurate measurement and calculation of component values (25%)
- Successful completion of all tasks (30%)
- Correct answers to application questions (20%)