A heat sensitive resistor made of a semiconductor is called?

Step 1: Analyze the question The question asks for the name of a device that is (a) a resistor, (b) made of a semiconductor, and (c) sensitive to heat (temperature).

Step 2: Explain the concept The word comes from combining two words:

• Thermo = heat/temperature
• Resistor = a component that opposes current flow

So a thermistor ("thermal resistor") is a semiconductor device whose resistance changes noticeably with temperature. There are two types:

• NTC (Negative Temperature Coefficient): resistance decreases as temperature rises (the most common).
• PTC (Positive Temperature Coefficient): resistance increases as temperature rises.

Step 3: Check each option

• A. Thermometer: a general instrument for measuring temperature. It is not specifically a semiconductor resistor.
• B. Thermostat: a switch-based device that keeps temperature constant, as in irons, refrigerators and water heaters.
• C. Thermistor: a heat-sensitive semiconductor resistor. This matches the description.
• D. Thermopile: a number of thermocouples connected in series, used to detect or measure radiant heat. It is not a resistor.

Step 4: Answer The correct option is C. thermistor.

Exam tip: Break the word apart. "Thermo" + "(res)istor" = thermistor. In the same way, a photoresistor (LDR) is a light-sensitive resistor. Also remember that a thermostat stats (keeps constant) the temperature, while a thermopile is a pile (stack) of thermocouples.