Wire wound resistances used in resistance boxes are made up of

Options

A. Iron
B. Copper
C. Silver
D. Manganin

Answer

To solve the question regarding the materials used in wire wound resistances in resistance boxes, let's analyze the options provided step by step.

### Step 1: Understanding Wire Wound Resistors
Wire wound resistors are made by winding a wire around an insulating core. This construction allows for precise resistance values and better heat dissipation.

**Hint:** Think about the properties of materials used in resistors, especially their thermal stability.

### Step 2: Analyzing the Options
We have four options to consider:
1. Iron
2. Copper
3. Silver
4. Manganin

**Hint:** Consider the electrical properties and temperature coefficients of resistance for each material.

### Step 3: Evaluating Each Material
- **Iron:** This is a good conductor but has a high temperature coefficient of resistance, meaning its resistance changes significantly with temperature. This makes it unsuitable for wire wound resistors.

- **Copper:** While copper is an excellent conductor and widely used in electrical applications, it also has a significant temperature coefficient, which can lead to variations in resistance with temperature changes.

- **Silver:** Silver has the lowest resistivity of all metals and is an excellent conductor. However, like copper, it has a high temperature coefficient, making it less suitable for applications requiring stable resistance.

- **Manganin:** Manganin is an alloy that has a very low temperature coefficient of resistance, making it highly stable across a range of temperatures. This property makes it ideal for use in wire wound resistors.

**Hint:** Look for materials that maintain stable resistance across varying temperatures.

### Step 4: Conclusion
Based on the analysis, the correct answer is **Manganin**. This alloy is specifically chosen for wire wound resistors due to its low sensitivity to temperature changes.

**Final Answer:** The wire wound resistances used in resistance boxes are made up of **Manganin**.