Question

Why does resistance decrease with an increase in temperature?

Answer 1

Actually, resistance typically increases with an increase in temperature for most conductors. This is due to the increased lattice vibrations within the material as the temperature rises, which impedes the flow of electrons and increases resistance.

However, there are materials called superconductors that exhibit a drastic drop in resistance below a certain critical temperature. For these materials, resistance decreases to zero when cooled below this critical temperature. But in the context of most conductors, like metals, resistance increases with temperature.

Answer 2

Actually, resistance typically **increases** with an increase in temperature for most conductive materials. Here’s a detailed explanation:

### Electrical Resistance and Temperature

**1. Basic Concept:**
Resistance (\(R\)) in a material is defined as the opposition to the flow of electric current. It can be expressed by Ohm's Law:

\[ R = \frac{V}{I} \]

where \(V\) is the voltage across the material, and \(I\) is the current flowing through it.

**2. Behavior with Temperature:**
For most metals and conductive materials, resistance increases with temperature. This is because as the temperature rises, the atoms in the material vibrate more intensely due to increased thermal energy. These vibrations create more collisions between the electrons (which carry the current) and the atoms, leading to increased resistance.

**3. Mathematical Representation:**
The temperature dependence of resistance can be expressed by:

\[ R_T = R_0 \left(1 + \alpha(T - T_0)\right) \]

where:
- \(R_T\) is the resistance at temperature \(T\),
- \(R_0\) is the resistance at a reference temperature \(T_0\),
- \(\alpha\) is the temperature coefficient of resistance.

For metals, \(\alpha\) is positive, indicating that resistance increases with temperature.

**4. Semiconductors and Insulators:**
In contrast to metals, semiconductors and insulators show a decrease in resistance with an increase in temperature. In semiconductors, the number of charge carriers (electrons and holes) increases with temperature, leading to lower resistance.

**5. Practical Implications:**
- **In Electronics:** High temperatures can lead to increased resistance in metal wires and components, which can affect the performance of electronic devices.
- **In Temperature Sensors:** Materials with a known resistance-temperature relationship are used in temperature sensors (like RTDs or thermistors) to measure temperature accurately.

So, in summary, while resistance typically increases with temperature for metals due to increased atomic vibrations causing more collisions with electrons, it decreases with temperature for semiconductors due to an increase in the number of charge carriers.