Give an exmple of amateral each for which temperature coefficient of resistivity is (i) positive, (ii) negative.

Answer

To answer the question regarding examples of materials with positive and negative temperature coefficients of resistivity, we can follow these steps:

### Step 1: Define Temperature Coefficient of Resistivity
The temperature coefficient of resistivity (α) is a measure of how much a material's resistivity changes with temperature. It is defined mathematically as:
\[ \rho(T) = \rho_0(1 + \alpha(T - T_0)) \]
where:
- \(\rho(T)\) is the resistivity at temperature \(T\),
- \(\rho_0\) is the resistivity at a reference temperature \(T_0\),
- \(\alpha\) is the temperature coefficient of resistivity.

### Step 2: Identify Positive Temperature Coefficient of Resistivity
For materials with a positive temperature coefficient of resistivity, as the temperature increases, the resistivity also increases. This behavior is typical for metals.

**Example:** Copper (Cu) is a metal that has a positive temperature coefficient of resistivity. As the temperature of copper increases, its resistivity increases.

### Step 3: Identify Negative Temperature Coefficient of Resistivity
For materials with a negative temperature coefficient of resistivity, as the temperature increases, the resistivity decreases. This is commonly observed in semiconductors.

**Example:** Silicon (Si) is a semiconductor that has a negative temperature coefficient of resistivity. As the temperature of silicon increases, its resistivity decreases.

### Final Answer
- **Material with Positive Temperature Coefficient of Resistivity:** Copper (Cu)
- **Material with Negative Temperature Coefficient of Resistivity:** Silicon (Si)

---