An aluminium wire `7.5 m` long is connected in parallel with a copper wire `6 m` long. When a current of `5 A` is passed through the combination, it is found that the current in the aluminium wire is `3 A`. The diameter of the aluminium wire is `1 mm`. Determine the diameter of the copper wire. Resistivity of copper is `0.017 muOmega-m` and that of the aluminium is `0.028 muOmega-m`.

Explanation

To solve the problem, we need to find the diameter of the copper wire when it is connected in parallel with an aluminum wire. We will use the given data and the relationship between resistance, resistivity, length, and cross-sectional area.

### Step-by-Step Solution:

1. **Identify Given Values**:
- Length of aluminum wire, \( L_1 = 7.5 \, \text{m} \)
- Length of copper wire, \( L_2 = 6 \, \text{m} \)
- Current through aluminum wire, \( I_1 = 3 \, \text{A} \)
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