Question 1: Explain what an LDR (Light-Dependent Resistor) is and how it responds to changes in light intensity.

Answer: An LDR is a resistor whose resistance decreases as the light intensity falling on it increases. It responds to light by changing its resistance based on the brightness.

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

Answer: A thermistor is a resistor whose resistance varies with temperature. In NTC thermistors, resistance decreases as temperature increases; in PTC thermistors, resistance increases with temperature.

Question 3: Which type of thermistor is most commonly used for temperature measurement? Explain your choice.

Answer: NTC thermistors are most commonly used for temperature measurement because their resistance decreases predictably as temperature increases, allowing accurate sensing.

Question 1: Explain why the resistance of an LDR decreases in bright light and increases in darkness.

Answer: In bright light, more photons hit the LDR, freeing more charge carriers and decreasing resistance. In darkness, fewer photons mean fewer charge carriers, increasing resistance.

Question 2: Describe how a thermistor can be used as a temperature sensor in household appliances.

Answer: A thermistor is connected to a circuit so that changes in resistance with temperature alter the current flow, allowing the device to monitor and respond to temperature changes in appliances like thermostats.

Question 1: Calculate the resistance of an LDR when it is exposed to bright light if its resistance in darkness is 1 MΩ and it decreases to 10 kΩ in bright light. Use the formula R = V/I, assuming voltage and current are constant.

Answer: Resistance decreases from 1,000,000 Ω to 10,000 Ω in bright light.

Question 2: A thermistor has a resistance of 50 kΩ at 25°C and 5 kΩ at 75°C. Determine the temperature coefficient of resistance per degree Celsius.

Answer: Temperature coefficient = (R2 - R1) / (R1 * (T2 - T1)) = (5,000 - 50,000) / (50,000 * (75 - 25)) = -0.002 per °C.

Question 3: If an LDR's resistance drops from 100 kΩ to 10 kΩ when the light level increases, what does this indicate about the light environment?

Answer: It indicates that the light environment has become brighter.

Question 1: Describe a simple experiment to test how an LDR responds to different light sources. Include variables to control and safety precautions.

Answer: Set up an LDR in a circuit connected to a voltmeter or LED. Expose it to various light sources (sunlight, lamp, darkness). Control variables like distance and light intensity. Ensure safety by avoiding direct looking into bright light sources and handling electrical components carefully.

Question 2: Identify the independent and dependent variables in an experiment testing the resistance change of a thermistor with temperature.

Answer: Independent variable: Temperature; Dependent variable: Resistance of the thermistor.

Question 1: Explain how LDRs are used in automatic street lighting systems.

Answer: LDRs detect ambient light levels; when it gets dark, resistance increases, activating the street lights to turn on automatically.

Question 2: Describe a scenario where thermistors are critical in industrial temperature control systems.

Answer: Thermistors are used in industrial ovens or HVAC systems to monitor and regulate temperature accurately, ensuring safety and efficiency.