A long horizontal wire `AB`, which is free to move in a vertical plane and carries a steady current of `20 A`, is in equilibrium at a height of `0.01 m` over another parallel long wire `CD` which is fixed in a horizontal plane and carries a steady current of ` 30 A`, as shown in figure. Shown that when `AB` is slightly depressed, it executes simple harmonic motion. Find the period of oscillations.