6. When does a coil's self-induction change? (1) A coil's number of turns is reduced. (2) A rod made of iron is inserted into it. Justify.
Answer (1)
Self-induction of a coil, also known as inductance, is the property of the coil that enables it to oppose any change in the current flowing through it by inducing an electromotive force (emf) in itself. This property depends on several factors:
Number of Turns in a Coil:
The inductance of a coil is directly proportional to the square of the number of turns in the coil. Therefore, if the number of turns in the coil is reduced, the self-inductance of the coil decreases. This is because with fewer turns, there is less wire through which the magnetic field lines can pass, reducing the total magnetic flux linkage and thereby decreasing inductance.
Formula: L ∝ N 2 , where L is the inductance and N is the number of turns.
Introducing an Iron Rod:
Inserting a rod made of iron (or any ferromagnetic material) into the coil increases the coil’s inductance. This is because iron has a high permeability, which means it allows the magnetic field lines to pass through it more easily than air. The increased magnetic flux linkage due to the presence of the iron core increases the inductance of the coil.
Additionally, the presence of a ferromagnetic core can concentrate the magnetic field lines within the coil, making the field stronger and further increasing inductance.
In summary, reducing the number of turns decreases self-induction, whereas introducing an iron rod into the coil increases it. These changes occur because both modifications affect the coil’s ability to support and maintain a magnetic field.
