Identify the incorrect statement regarding a superconducting wire

Options

A. Transport current flows through its surface
B. Transport current flows through the entire area of crossection of the wire
C. It exhibits zero elactrical resistivity and expels applied magnetic field .
D. It is used to produce large magnetic field

Explanation

To identify the incorrect statement regarding a superconducting wire, let's analyze the properties of superconductors step by step.

### Step-by-Step Solution:

1. **Understanding Superconductors**:
- A superconductor is a material that exhibits zero electrical resistance when cooled below a certain critical temperature. This means that electric current can flow through it without any energy loss.

**Hint**: Remember that superconductors have unique properties that distinguish them from normal conductors, particularly at low temperatures.

2. **Current Flow in Superconductors**:
- In superconductors, the current does not flow through the entire cross-sectional area of the wire. Instead, it flows through a thin layer at the surface of the wire. This is a characteristic behavior of superconductors, known as the "Meissner effect", which causes them to expel magnetic fields.

**Hint**: Consider how current behaves differently in superconductors compared to normal conductors.

3. **Evaluating the Statements**:
- **Statement A**: "Transport current flows through its surface."
- This statement is correct because, in superconductors, the current tends to flow near the surface due to the expulsion of magnetic fields.

- **Statement B**: "Transport current flows through the entire area of cross section of wire."
- This statement is incorrect. As mentioned, the current in superconductors does not flow through the entire cross-section but rather through a surface layer.

- **Statement C**: "It exhibits zero electrical resistivity and expels applied magnetic field."
- This statement is correct. Superconductors have zero resistivity and expel magnetic fields due to the Meissner effect.

- **Statement D**: "It is used to produce large magnetic fields."
- This statement is also correct. Superconductors can carry large currents without resistance, allowing them to generate strong magnetic fields.

4. **Conclusion**:
- The incorrect statement regarding a superconducting wire is **Statement B**: "Transport current flows through the entire area of cross section of wire."

### Final Answer:
The incorrect statement is: **Transport current flows through the entire area of cross section of wire.**