A circular coil `P` of `100` turns and radius `2cm` is placed coaxially at the centre of another circular coil `Q` of `100` turns and radius `20cm` . Calculate (a) the mutual inductance of the coils
(b) the induced emf in coil `P` when the current in the coil `Q` decreases from `5A` to `3A` in `0.04` sec (Take `pi^(2)=10)`

Explanation

To solve the problem step by step, we will first calculate the mutual inductance of the coils and then find the induced EMF in coil P when the current in coil Q changes.

### Step 1: Calculate the Mutual Inductance (M)

The formula for mutual inductance \( M \) between two coaxial coils is given by:

\[
M = \frac{n_1 n_2 \mu_0 \pi r_1^2}{2 r_2}
...