47. What capacitance exists not through design but simply because two conducting surfaces are relatively close to each other?

The following three impedances are connected in series across a 40 V, 20 kHz supply: a 
resistance of 8 Ω, a coil of inductance 130 μH and 5 Ω resistance, and a 10 Ω resistor in 
series with a 0.25 µF capacitor. Sketch a neat diagram representing this network, and 
calculate:
5.1.1 The inductive and capacitive reactance’s. (4)
5.1.2 The magnitude and phase angle of the circuit impedance. (4)
5.1.3 The voltage drops across resistance, inductance and capacitance.

First Part

In the toroidal coil of the figure below the outer radius is equal to 5cm and the
internal with 4cm. The core is made of ferromagnetic material, the
coil has 400 + 13 coils and is leaked by a current of 0.3 A. The relative magnetic
permeability of ferromagnetic material is 2000.
1. Calculate the magnetic flux Φ in the core.
2. Calculate magnetic induction B.

Second Part

The toroidal coil itself is made of ferromagnetic material M1929, and the coil
it has 400 + 13 spirals.
1. How much current will need to pass through the coil in order to grow
magnetic flux equal to 0.12 mWb.
2. How much current will need to pass through the coil in order to grow
magnetic flux equal to 0.06 mWb.