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

Answer: An LDR is a resistor whose resistance decreases as light intensity increases; it works based on photoconductivity, where light photons increase charge carriers, reducing resistance.

Question 2: Describe the working principle of a thermistor and differentiate between NTC and PTC thermistors.

Answer: A thermistor is a resistor whose resistance varies with temperature; NTC thermistors decrease resistance as temperature rises, while PTC thermistors increase resistance with temperature.

Question 1: An LDR has a resistance of 10 kΩ in darkness and 1 kΩ in bright light. Calculate the percentage decrease in resistance when moving from darkness to bright light.

Answer: Percentage decrease = [(10,000 - 1,000) / 10,000] × 100 = 90%

Question 2: A thermistor has a resistance of 50 kΩ at 20°C and 10 kΩ at 80°C. Using the formula R = R0 × e^(β(1/T - 1/T0)), estimate the β value assuming T0 = 293K and T = 353K.

Answer: β ≈ 3400 K (approximate calculation)

Question 1: Outline a simple experiment to measure how the resistance of an LDR varies with different light intensities. Include variables to control and safety precautions.

Answer: Set up a circuit with an LDR, a voltmeter, and a power supply. Vary the light intensity using a lamp or natural light while keeping the distance constant. Measure resistance at each light level. Control variables include light source distance and ambient temperature. Safety precautions include avoiding direct exposure to intense light to prevent eye damage and ensuring the circuit is correctly connected to prevent short circuits.

Question 1: A thermistor's resistance was recorded at different temperatures: 20°C (50 kΩ), 40°C (25 kΩ), 60°C (12.5 kΩ). Describe the relationship between temperature and resistance and explain what this indicates about the thermistor type.

Answer: Resistance decreases as temperature increases, indicating it is an NTC thermistor. This inverse relationship shows resistance is thermally sensitive, decreasing with rising temperature.

Question 1: Explain how LDRs are used in automatic street lighting systems. Include the principle of operation and the advantages of such systems.

Answer: LDRs detect ambient light levels and control street lights accordingly. When light falls below a threshold, resistance increases, activating a circuit that turns on the lights. Advantages include energy efficiency, automatic operation without human intervention, and reduced light pollution.

Question 1: Describe how thermistors are used in temperature control systems within household appliances such as refrigerators or ovens.

Answer: Thermistors monitor temperature changes and regulate heating or cooling elements to maintain desired temperatures, ensuring efficiency and safety in appliances.