A long solenoid is fabricated by closely winding a wire of radius 0.5 mm over a cylindrical nonmagnetic frame so that the successive turns nearly touch each other. What would be the magnetic field B at the centre of the solenoid if it carries a current of 5 A?

Explanation

To find the magnetic field \( B \) at the center of a long solenoid carrying a current of 5 A, we can follow these steps:

### Step 1: Identify the given parameters
- Radius of the wire \( r = 0.5 \, \text{mm} = 0.5 \times 10^{-3} \, \text{m} \)
- Current \( I = 5 \, \text{A} \)

### Step 2: Calculate the diameter of the wire
The diameter \( d \) of the wire is given by:
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