Why are alloys used for making standard resistance coils?

Options

A. Resistance to corrosion
B. Poor conductivity
C. heaviness
D. All of these

Answer

To answer the question "Why are alloys used for making standard resistance coils?", we can break down the explanation into several key points:

### Step-by-Step Solution:

1. **High Resistance or High Resistivity**:
- Alloys typically have a higher resistivity compared to pure metals. This property is crucial for resistance coils as it allows them to provide a stable and consistent resistance value.

2. **Temperature Independence**:
- The resistance of alloys is relatively independent of temperature changes. This means that when current passes through the coil and generates heat, the change in temperature does not significantly affect the resistance. This stability is essential for accurate measurements in standard resistance coils.

3. **Corrosion Resistance**:
- Alloys are generally more resistant to corrosion compared to pure metals. This property ensures that the resistance coils have a longer lifespan, as they are less likely to degrade over time due to environmental factors. For example, pure iron can rust easily, whereas iron alloys (like steel) are much more durable.

4. **Heaviness**:
- Alloys often have a higher density, which can be beneficial in certain applications where weight is a consideration. This can contribute to the stability of the coils in their operational environment.

### Conclusion:
Given these points, alloys are preferred for making standard resistance coils due to their high resistivity, temperature stability, corrosion resistance, and appropriate weight. Therefore, the answer to the question is that all these properties make alloys ideal for this application.