Question 1: What is an LDR and how does it respond to different levels of light?

Answer: An LDR (Light-Dependent Resistor) is a sensor whose resistance decreases as light intensity increases. It responds to light by allowing more current to pass through as it gets brighter.

Question 2: Explain the principle behind a thermistor and how its resistance changes with temperature.

Answer: A thermistor is a resistor whose resistance varies with temperature. It can be a Negative Temperature Coefficient (NTC) thermistor, where resistance decreases as temperature increases, or a Positive Temperature Coefficient (PTC) thermistor, where resistance increases with temperature.

Question 1: An LDR has a resistance of 1 MΩ in darkness and 10 kΩ under bright light. Calculate the ratio of resistance between dark and bright conditions.

Answer: Resistance ratio = 1,000,000 Ω / 10,000 Ω = 100

Question 2: A thermistor has a resistance of 50 kΩ at 25°C and 10 kΩ at 75°C. Using the NTC thermistor formula, estimate the resistance at 50°C. (Assume a linear approximation for simplicity.)

Answer: Approximate resistance at 50°C ≈ 32.5 kΩ based on linear interpolation between values.

Question 1: Describe a simple experiment to test how an LDR responds to changing light levels. Include variables to be controlled and safety precautions.

Answer: Set up a circuit with an LDR, a resistor, and a voltmeter. Expose the LDR to varying light sources or distances, and record resistance or voltage readings. Control variables such as light intensity, distance, and ambient conditions. Safety precautions include avoiding direct intense light sources that could harm eyes and ensuring proper circuit connections to prevent short circuits.

Question 2: Identify two industries or everyday devices where LDRs or thermistors are used, and explain their function.

Answer: LDRs are used in outdoor light sensors for street lighting, turning lights on at dusk. Thermistors are used in digital thermometers to measure body temperature or in thermostats to control heating systems.

Question 1: A thermistor's resistance drops from 100 kΩ to 20 kΩ as temperature increases from 20°C to 60°C. Describe what this indicates about the thermistor’s type and its response to temperature.

Answer: This indicates it is an NTC thermistor, as resistance decreases with increasing temperature.

Question 2: In a circuit, an LDR’s resistance decreases as the light intensity increases. If the resistance drops from 500 kΩ to 50 kΩ, what does this imply about the change in lighting conditions?

Answer: It implies that lighting conditions have become brighter, as the LDR’s resistance decreases with increased light intensity.