To identify a diode, LED, a transistor, an IC, resistor and capacitor from collection of such items

Aim

To identify a diode, an LED, a transistor, an IC, a resistor and a capacitor from a mixed collection of such items.

Apparatus and Material

A collection of a diode, an LED, a transistor, an IC, a resistor, a capacitor, and a multimeter.

Theory

For identification, the appearance and working of each item will have to be considered.
1. A diode is a two-terminal device. It conducts when forward biased and does not conduct when reverse biased. It does not emit light while conducting. Hence, it does not glow.
2. An LED (light-emitting diode) is also a two-terminal device. It also conducts when forward biased and does not conduct when reverse biased. It emits light while conducting. Hence, it glows.
3. A transistor is a three-terminal device. The terminals represent emitter (E), base (B) and collector (C).
4. An IC (integrated circuit) is a multi-terminal device in the form of a chip.
5. A resistor is a two-terminal device. It is conducted when either forward-biased or reverse-biased. (In fact, there is no forward or reverse bias for a resistor). It conducts even when operated with A.C. voltage.
6. A capacitor is also a two-terminal device. It does not conduct when either forward-biased or reverse-biased. When a capacitor is connected to a D.C. source, the multimeter shows full-scale current initially but it decays to zero quickly. It is because initially, a capacitor draws a charge.

Procedure

1. If the item has four or more terminals and has the form of a chip, it is an IC (integrated circuit).
2. If the item has three terminals, it is a transistor.
3. If the item has two terminals, it may be a diode, an LED, a resistor or a capacitor.
To differentiate proceed as ahead.
4. Put the selector on-resistance R of the multimeter to check the continuity. The probe metal ends are inserted in the terminal marked on the multimeter as common and P (or + ve).

If such the black one is in common and the red probe is in P (or + ve). On touching the two ends of the device to the two other metal ends of probes.

1. If the pointer moves when voltage is applied in one way and does not move when reversed and there is no light emission, the item is a diode.
2. If the pointer moves when voltage is applied in one way and does not move when reversed and there is light emission, the item is an LED.
3. If the pointer moves when voltage is applied in one way and also when reversed, the item is a resistor.
4. If the pointer does not move when voltage is applied in one way and also when reversed, the item is a capacitor.

Result

A diode, an LED, IC, resistor or capacitor can be identified.

Electronic Devices Based on Number of Terminals

Classification of Electronic Components Based on Current Flow

Precautions

• Handle all electronic components gently to avoid bending their leads.
• Ensure the multimeter is correctly set to the resistance (Ω) mode before testing.
• Always start with the lowest range of resistance for accurate readings.
• Do not apply excessive pressure on component terminals while using the multimeter probes.
• Never connect the multimeter in resistance mode to a powered circuit.
• Observe polarity carefully while checking diodes and LEDs.
• Avoid touching the metal parts of probes during measurement to prevent incorrect readings.
• Ensure capacitors are fully discharged before testing to avoid damage to the multimeter.
• Keep components dry and clean for proper identification.
• Verify readings more than once to avoid errors and confirm the component type.

Sources of Error

1. The multimeter should show zero resistance when its metal leads are touched together. If it does not show zero, adjust it using the zero-adjustment knob. If proper zero adjustment is not done, the measured resistance will be incorrect.
2. While measuring resistance, the metal ends of the multimeter leads should not be touched by hand. The body resistance comes in parallel with the component resistance and affects the measured value, leading to error.

Solved Examples Based to Identify a Diode, LED, Transistor, IC, Resistor and Capacitor From Collection of Such Items

Example 1: In column A, some names of the electronic components and in column B, the number of its terminals are given. Match each other.

Column A
(1) IC integrated
(2) transistor
(3) LED

Column B
(a) Three
(b) One
(c) Three or more than three
(d) Two

1) $1 \rightarrow \mathrm{c}, 2 \rightarrow \mathrm{a}, 3 \rightarrow \mathrm{d}$
2) $1 \rightarrow \mathrm{d}, 2 \rightarrow \mathrm{c}, 3 \rightarrow \mathrm{b}$
3) $1 \rightarrow \mathrm{c}, 2 \rightarrow \mathrm{b}, 3 \rightarrow \mathrm{a}$
4) $1 \rightarrow \mathrm{b}, 2 \rightarrow \mathrm{a}, 3 \rightarrow \mathrm{c}$

Solution:

To identify a diode, LED, transistor, IC, resistor and capacitor from the collection of such items

* If the item has four or more terminals and is in the form of a chip then it is an IC ( Integrated Chip)

* If the item has three terminals it is a transistor

* If it has two items it may be a diode, LED, resistor or capacitor

* Look for the colour band. If it is a set of three colours it is a resistor

* If the multimeter shows an equal deflection in both directions the component is a resistor

wherein

* If the multimeter does not show any deflection the component is a diode

* If the multimeter shows less deflection in other directions it is LED

* If it does not show any deflection on connecting terminals in either way, it is a capacitor

Result:

A diode, an LED, IC, resistor or capacitor can be identified.

Hence, the answer is the option (1).

Example 2: Which of the following will NOT be observed when a multimeter (operating in resistance measuring mode) probes connected across a component, are just reversed?

1)Multimeter shows an equal deflection in both cases i,e. before and after reversing the probes if the chosen component is a resistor.

2) Multimeter shows NO deflection in both cases i,e. before and after reversing the probes if the chosen component is a capacitor.

3) The multimeter shows a deflection, accompanied by a splash of light out of the connected component in one direction and NO deflection on reversing the probes if the chosen component is LED.

4)Multimeter shows NO deflection in both cases i,e. before and after reversing the probes if the chosen component is metal wire.

Solution:

1. No matter, how we connect the resistance across the multimeter It shows the same deflection.

2. The multimeter shows deflection when it connects with a capacitor.

3. If we assume that LED has negligible resistance then the multimeter shows no deflection for the forward bias but when it connects in the reverse direction, it breaks down so splash of light out.

4. The resistance of the metal wire may be zero, so no deflection in the multimeter.

Hence, the answer is the option (2).

Summary

To identify electronic components such as diodes, LEDs, transistors, ICs, resistors, and capacitors, look for their specific features. Diodes and LEDs have two leads, with LEDs emitting light. Transistors have three leads and a specific shape, often with part numbers. ICs are small chips with multiple pins and part numbers. Resistors are cylindrical with colour bands for resistance values, while capacitors are cylindrical or rectangular, with capacitance values marked. By observing these characteristics, you can accurately identify each component in your collection.