The magnetic field at a point inside a 2.0 mH inductor coil becomes 0.80 of its maximum value in `20 mu s ` when the inductor is joined to a battery. Find the resistance of the circuit.

Explanation

To solve the problem step by step, we will use the relationship between the magnetic field in an inductor, the time constant, and the resistance of the circuit.

### Step 1: Understand the given values
- Inductance \( L = 2.0 \, \text{mH} = 2 \times 10^{-3} \, \text{H} \)
- Time interval \( t = 20 \, \mu s = 20 \times 10^{-6} \, \text{s} \)
- The magnetic field reaches \( 0.8 \) of its maximum value.

### Step 2: Write the expression for current in an inductor
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