A long solenoid is formed by winding 20 turns `cm^-1`. What current is necessary to produce a magnetic field of `20 mT` inside the solenoid?

Explanation

To solve the problem of finding the current necessary to produce a magnetic field of 20 mT inside a long solenoid with 20 turns per centimeter, we can follow these steps:

### Step 1: Understand the formula for the magnetic field inside a solenoid
The magnetic field \( B \) inside a long solenoid is given by the formula:
\[ B = \mu_0 n I \]
where:
...