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

Answer: An LDR is a resistor whose resistance decreases as light intensity increases. It operates on the principle that light photons cause electron excitation in the material, reducing resistance.

Question 2: Describe the main difference in resistance change between an LDR and a Thermistor when temperature varies.

Answer: An LDR's resistance is affected by light, not temperature, whereas a Thermistor's resistance changes significantly with temperature, decreasing in NTC types as temperature rises.

Question 1: An LDR has a resistance of 10 kΩ in darkness and 1 kΩ under bright light. Calculate the percentage decrease in resistance when moving from darkness to bright light. (Use the formula: Percentage change = (Initial - Final) / Initial × 100%)

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

Question 2: A Thermistor's resistance is 50 kΩ at 20°C and drops to 10 kΩ at 50°C. Calculate the temperature coefficient of resistance per degree Celsius. (Use the formula: α = (R2 - R1) / (R1 × ΔT)) where ΔT = T2 - T1.

Answer: α = (10,000 - 50,000) / (50,000 × (50 - 20)) = -40,000 / (50,000 × 30) = -0.0267 Ω/°C

Question 1: Describe a simple experiment to measure how the resistance of an LDR varies with changing light levels. Include the key variables and safety precautions.

Answer: Set up a circuit with the LDR connected to a voltmeter and a fixed power supply. Vary the light intensity using a lamp or natural light, and record the voltage across the LDR to infer resistance. Variables include light intensity (independent), resistance (dependent), and voltage (measured). Precautions involve avoiding direct exposure to intense light sources and ensuring correct circuit connections to prevent short circuits.

Question 2: Identify two factors that can affect the accuracy of resistance measurements in experiments involving Thermistors.

Answer: Factors include contact resistance at connection points and ambient temperature fluctuations affecting the Thermistor's resistance.

Question 1: In a room, an LDR's resistance was measured as 20 kΩ in the morning and 2 kΩ in the afternoon. Explain what environmental factor caused this change and how it affects the circuit.

Answer: The change is caused by increased light intensity in the afternoon, which decreases the LDR's resistance, allowing more current flow in the circuit.

Question 2: A Thermistor's resistance measurements at different temperatures are as follows: 10 kΩ at 40°C, 7 kΩ at 50°C, and 4.9 kΩ at 60°C. Describe the trend and its significance for temperature sensing applications.

Answer: Resistance decreases with increasing temperature, indicating an NTC Thermistor, which is useful for temperature sensing due to its predictable resistance change.

Question 1: Explain how Thermistors are used in modern household appliances to improve safety and energy efficiency. Provide specific examples.

Answer: Thermistors are used in thermostats within appliances like refrigerators and ovens to monitor and regulate temperature precisely, preventing overheating and reducing energy consumption by adjusting heating or cooling systems accordingly.

Question 2: A street lighting system uses an LDR to turn on lights at night automatically. Discuss the advantages of using LDRs for this purpose compared to manual switching.

Answer: Using LDRs allows automatic operation based on ambient light levels, saving energy, reducing manual effort, and ensuring lights are only on when needed, improving efficiency and convenience.