The LDR (Light Dependent Resistor) is classified as a passive sensor.

Explanation:

• Passive sensors are sensors that do not require an external power source to function. They detect and respond to a physical parameter (like light in the case of the LDR) by changing their own physical properties (in this case, resistance).
• LDRs change their resistance based on the amount of light they are exposed to but do not require any external power for detection. The sensor's resistance varies depending on the intensity of light, and this change can be measured by a circuit.

Comparison:

• Active Sensors require an external power source to operate and generate a signal (e.g., ultrasonic sensors, temperature sensors with built-in signal generation).
• Passive Sensors simply respond to changes in their environment and typically modify a property (such as resistance, capacitance, or inductance) without needing an external power supply for operation.

Applications:

• Automatic Lighting Systems: LDRs are commonly used to automatically turn on lights when it gets dark (such as street lighting or night lamps).
• Solar Garden Lights: They detect light intensity to turn on lights at night.
• Light Metering: Used in devices for measuring light intensity.