Question 1: Define a Light Dependent Resistor (LDR) and explain how its resistance varies with light intensity.

Answer: An LDR is a resistor whose resistance decreases as the light intensity increases.

Question 2: Describe the basic working principle of a Thermistor and how its resistance changes with temperature.

Answer: A Thermistor is a resistor whose resistance varies with temperature; it decreases in NTC thermistors as temperature rises.

Question 3: Explain why LDRs are useful in automatic lighting systems.

Answer: LDRs can detect light levels and automatically turn lights on or off based on ambient light conditions.

Question 1: An LDR is connected in a circuit with a supply voltage of 12 V. When exposed to bright light, the current flowing through it is 0.6 mA. Calculate the resistance of the LDR in this condition.

Answer: Resistance = 12 V / 0.0006 A = 20,000 Ω (20 kΩ)

Question 2: A thermistor has a resistance of 10 kΩ at 25°C. When the temperature increases to 50°C, its resistance drops to 4 kΩ. Calculate the approximate temperature coefficient of resistance.

Answer: Using ΔR/R = α ΔT, α ≈ (4,000 - 10,000) / (10,000 × (50 - 25)) = -0.0024 per °C

Question 1: Outline the experimental procedure to investigate the relationship between light intensity and LDR resistance, including variables and safety precautions.

Answer: Set up a circuit with an LDR, a voltmeter, and a variable light source. Keep the supply voltage constant. Vary the light intensity using a lamp or different distances. Measure the voltage across the LDR and calculate resistance. Control variables like temperature. Ensure the circuit is correctly insulated and avoid direct contact with electrical components to prevent shocks.

Question 1: A Thermistor's resistance at various temperatures is recorded as follows: 0°C - 50 kΩ, 25°C - 10 kΩ, 50°C - 4 kΩ. Describe the trend and explain what this indicates about the thermistor's characteristics.

Answer: Resistance decreases as temperature increases, indicating it is an NTC thermistor, which is common for temperature sensing.

Question 1: Describe how LDRs are used in automatic street lighting systems and the advantages of using them.

Answer: LDRs detect ambient light levels to turn street lights on or off automatically, saving energy and reducing manual control.

Question 2: Explain why Thermistors are preferred in digital thermostats over simple resistors, considering their properties.

Answer: Thermistors provide accurate and responsive temperature readings due to their resistance change with temperature, enabling precise control.