A current of i ampere is passing in an aluminium wire whose cross-section is ` A m^2`
The current density in the wire is given by

Options

A. `j=iA`
B. `j=i//A`
C. `j=A//i`
D. None of these

Explanation

To find the current density in an aluminium wire, we can use the formula for current density, which is defined as the current flowing through a unit cross-sectional area of the wire.

### Step-by-Step Solution:

1. **Understand the Definitions**:
- Current (I) is the flow of electric charge, measured in amperes (A).
- Cross-sectional area (A) is the area of the wire's cross-section, measured in square meters (m²).
- Current density (J) is defined as the current per unit area.

2. **Write the Formula for Current Density**:
\[ J = \frac{I}{A} \]
where:
- \( J \) is the current density,
- \( I \) is the current in amperes,
- \( A \) is the cross-sectional area in square meters.

3. **Substitute the Given Values**:
- We know that the current \( I \) is given as \( i \) amperes and the cross-sectional area \( A \) is given as \( A \) m².
- Substitute these values into the formula:
\[ J = \frac{i}{A} \]

4. **Conclusion**:
- The expression for current density in the aluminium wire is:
\[ J = \frac{i}{A} \]

### Final Answer:
The current density in the wire is given by \( J = \frac{i}{A} \).

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