A thin but long, hollow, cylindrical tube of radius r carries a current i along its length. Find the magnitude of the magnetic field at a distance r/2 from the surface (a) inside the tube (b) outside the tube.

Explanation

To solve the problem of finding the magnetic field due to a long hollow cylindrical tube carrying a current \( i \), we will analyze two scenarios: (a) inside the tube and (b) outside the tube.

### Step-by-Step Solution

**Given:**
- Hollow cylindrical tube of radius \( r \)
- Current \( i \) flowing along its length
- We need to find the magnetic field at a distance \( \frac{r}{2} \) from the surface of the tube.
...