A thermistor is a type of resistor that's sensitive to temperature. In simpler terms, it's an electrical component whose resistance changes significantly with temperature changes.

There are two main types of thermistors:

Negative Temperature Coefficient (NTC): This is the most common type. In an NTC thermistor, resistance decreases as temperature increases. So, when it gets hotter, it becomes easier for electricity to flow through it.
Positive Temperature Coefficient (PTC): In contrast, a PTC thermistor's resistance increases with temperature. As it gets hotter, it becomes harder for electricity to flow.

Thermistors are typically made of semiconductor materials like metallic oxides. These materials are formed into various shapes like beads, discs, or cylinders and then encased in a protective coating like epoxy or glass.

what makes thermistors useful:

Temperature Measurement: By measuring the change in resistance, we can determine the temperature. They are very sensitive and can detect even small temperature variations.
Temperature Control: NTC thermistors are often used in feedback circuits for temperature control systems. As the temperature rises, the resistance drops, signaling the circuit to adjust and bring the temperature back down. PTC thermistors can also be used for resettable overcurrent protection.

Thermistors are widely used in various applications due to their small size, fast response time, and cost-effectiveness. Some common examples include:

Thermometers: Digital thermometers often use thermistors to sense temperature.
Thermostats: Thermistors play a key role in regulating temperature in appliances like refrigerators and AC units.
Engine coolant sensors: In cars, thermistors monitor engine coolant temperature.
Overheat protection: They can be used in devices to prevent overheating by cutting off power if the temperature gets too high.