If a long hollow copper pipe carries a current, then magnetic field is produced:

Options

A. inside the pipe only
B. outside the pipe only
C. both inside and outside the pipe
D. no where

Explanation

To determine the magnetic field produced by a long hollow copper pipe carrying a current, we can follow these steps:

### Step 1: Understand the Configuration
We have a long hollow copper pipe that carries an electric current. The pipe is hollow, meaning there is an empty space inside it.

### Step 2: Apply Ampère's Law
According to Ampère's Law, the magnetic field (B) around a current-carrying conductor can be determined by considering the current enclosed by an imaginary loop (Amperian loop) around the conductor.

### Step 3: Analyze the Inside of the Hollow Pipe
When we consider a loop inside the hollow portion of the pipe:
- The current enclosed by this loop is zero because there is no current flowing through the hollow space.
- Therefore, according to Ampère's Law, the magnetic field inside the hollow pipe (B_inside) is given by:
\[ B_{\text{inside}} = 0 \]

### Step 4: Analyze the Outside of the Hollow Pipe
Now, consider a loop outside the hollow pipe:
- The current enclosed by this loop is equal to the total current flowing through the pipe.
- Hence, the magnetic field outside the pipe (B_outside) is non-zero and can be calculated using Ampère's Law.

### Step 5: Conclusion
From the above analysis, we conclude that:
- The magnetic field inside the hollow copper pipe is zero.
- The magnetic field exists outside the hollow copper pipe.

Thus, the answer to the question is that the magnetic field is produced outside the pipe.

### Final Answer
The magnetic field is produced **outside the hollow copper pipe**.

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