Experiment - 7 :- A Different Type of Resistor

Combined Resistor Experiment   :- A different type of resistor while using the same basic circuit concepts (simple resistance measurement and a voltage divider).

Materials

• Digital Multimeter: Capable of measuring resistance (Ω) and DC voltage (V).

• Breadboard: For easy circuit construction.

• $9V$ Battery: A standard power source for the circuit.

• Fixed Resistor: A known value (e.g., 10kΩ) for a stable reference.

• Potentiometer: An adjustable resistor (e.g., 10kΩ).

• Thermistor: An NTC (Negative Temperature Coefficient) type.

• Photoresistor (LDR): A light-dependent resistor.

• Small Fan or Air Duster: To provide a cool breeze.

• Light Source: A flashlight or desk lamp.

• LED and Current-Limiting Resistor: A 330Ω resistor is a good choice to protect the LED.

• Containers: One with ice water, one with hot water.

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Part 1: Fixed Resistor and Potentiometer as a Reference   

This part sets the baseline for resistance and introduces the concept of a variable resistor.

1. Measure Fixed Resistor: Set your multimeter to measure resistance (Ω). Place the probes on the leads of the fixed resistor and note the reading. This value should be very close to the one indicated by the color code on the resistor itself.

2. Explore the Potentiometer: Connect the multimeter to the two outer terminals of the potentiometer. The resistance should remain constant, indicating the total resistance of the component. Now, connect the probes to a center terminal and one of the outer terminals. As you turn the knob, the resistance will change. This demonstrates its function as a manually adjustable resistor.

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Part 2: Characterizing the Thermistor (Temperature-Dependent Resistor) 

This part shows how resistance can be affected by temperature.

1. Resistance vs. Temperature: Connect the thermistor to the multimeter. Record its resistance at room temperature. Submerge the thermistor in the hot water and watch the resistance reading. For an NTC thermistor, the resistance will decrease. Then, place it in the ice water and observe the resistance increase significantly.

2. Build a Temperature-Sensing Circuit: Create a simple voltage divider on the breadboard using the thermistor and the potentiometer. Connect the 9V battery across the entire divider.

3. Observe Voltage Change: Measure the voltage across the thermistor with your multimeter. Blow a stream of air from a fan or air duster on the thermistor and watch the temperature and voltage change. The voltage will rise as the thermistor cools and its resistance increases.

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Part 3: Characterizing the Photoresistor (Light-Dependent Resistor)

This part demonstrates how a resistor's properties can be altered by light.

1. Resistance vs. Light: Connect the LDR to your multimeter. Place your hand over it or turn off the lights to create a dark environment. The multimeter will show a very high resistance value (often in the hundreds of kilo-ohms). Now, shine the light source directly onto the LDR. The resistance will drop to a very low value.

2. Build a Light-Sensing Circuit: Use the LDR and the potentiometer to build a voltage divider circuit on the breadboard. Connect the voltage divider's output to an LED (with a current-limiting resistor) to create a simple light-activated switch.

3. Demonstrate Function: In a dark room, the high resistance of the LDR will keep the LED from lighting up. When you shine a light on the LDR, its resistance drops, causing the voltage to shift and allowing current to flow to the LED, turning it on.