The thermistors are usually made of
(a) metals with low temperature coefficient of resistivity
(b) m

Q: Why can't we use standard copper wire as a thermistor?

Copper is a metal with a positive and very small temperature coefficient. Its resistance doesn't change enough with temperature to be a sensitive and practical temperature sensor.

Q: What does 'negative temperature coefficient' mean?

It means that as the temperature increases, the resistance of the material decreases. This inverse relationship is typical for semiconductors and metal oxides used in thermistors.

Q: Are all thermistors made of metal oxides?

While most NTC (Negative Temperature Coefficient) thermistors are made of metal oxides, there are also PTC (Positive Temperature Coefficient) thermistors made from different materials like doped barium titanate. However, metal oxides are the classic textbook example for highly sensitive temperature measurement.

Q: Why do metal oxides behave like this when heated?

Metal oxides often act as semiconductors. As temperature rises, more electrons gain enough thermal energy to jump into the conduction band, drastically lowering the electrical resistance.

Q: Is a thermistor an ohmic device?

No, thermistors are non-ohmic. Because their resistance changes with the temperature (which can be affected by the current passing through them due to self-heating), the V-I graph is not a straight line.

Question

The thermistors are usually made of

Options:

(A) metals with low temperature coefficient of resistivity

(B) metals with high temperature coefficient of resistivity

(C) metal oxides with high temperature coefficient of resistivity

(D) semiconducting materials having low temperature coefficient of resistivity

Sigma Percentile · Accepted Answer

### The Magic of Thermistors

Have you ever wondered how digital thermometers measure your body temperature so quickly and accurately? Or how your car's engine knows exactly when it's getting too hot? The secret lies in a tiny, unassuming component called a **thermistor**.

A thermistor is a portmanteau of the words 'thermal' and 'resistor'. Unlike standard resistors, which are designed to maintain a constant resistance regardless of temperature, a thermistor's entire purpose in life is to change its resistance drastically when the temperature changes.

### The Need for High Sensitivity

If we want to build a highly sensitive temperature sensor, we need a material whose resistance changes significantly with even a tiny change in temperature. This property is quantified by the **temperature coefficient of resistivity**, denoted by $\alpha$.

Normal metals, like copper or aluminum, have a positive temperature coefficient (PTC). This means their resistance increases as they get hotter. However, this change is very small. If we used a copper wire as a thermometer, the resistance change would be so minuscule that it would be incredibly difficult to measure accurately.

### Enter Metal Oxides

To achieve the extreme sensitivity required for a thermistor, engineers turn to semiconducting materials, specifically **sintered metal oxides**. These include oxides of manganese, nickel, cobalt, copper, and iron.

These metal oxides typically exhibit a **Negative Temperature Coefficient (NTC)**. This means that as the temperature increases, their resistance drops. And it doesn't just drop a little bit—it plummets!

Why does this happen? Because in a semiconductor, increasing the thermal energy excites more electrons across the bandgap into the conduction band. This massive influx of charge carriers drastically reduces the resistance.

### The Final Verdict

Because of this incredible property, metal oxides are the perfect candidates for making thermistors. They provide a **high temperature coefficient of resistivity**, making them incredibly sensitive to thermal changes.

So, the next time you see a temperature reading on a digital display, you can thank the fascinating quantum mechanics of metal oxides working tirelessly behind the scenes!

Animated Solution for Physics - Current Electricity: The thermistors are usually made of

Select Answer:

Visualized Solution

$Understanding Thermistors$

$Temperature Coefficient$

$Material Composition$

$Conclusion$

The Sigma Insight: Ohm's Law, Resistance and Electrical Power

The Magic of Thermistors

The Need for High Sensitivity

Enter Metal Oxides

The Final Verdict

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