What is toroid?
The solenoid bent into circular shape is called toroid.
Inductance of a toroid derivation
Consider a toroid having rectangular cross sectional area.The inner radius of the toroid is ‘a’ while outer radius is b.The number of turns of toroid is N.Let i be the current flowing through each turn of toroid. The magnetic field lines inside the solenoid is given as:
Where dA = hdr is the area of the elementary strip of toroid .Putting the value of ‘B’ from equation (1) we get:
Which is the relation for inductance of solenoid.The inductance L depends only on geometrical factors.