Short Answer:

Self-induction is the phenomenon in which a changing current in a coil produces an electromotive force (EMF) in the same coil. This happens because the current creates a magnetic field, and when the current changes, the magnetic field also changes, inducing a voltage in the coil itself. This induced EMF always opposes the change in current as per Lenz’s Law.

Self-induction is a property of every coil or conductor carrying changing current. The strength of this effect depends on the coil’s number of turns, shape, and core material. Self-induction is important in devices like inductors, transformers, and chokes.

Detailed Explanation:

Self-induction

Self-induction is a fundamental concept in electromagnetism and is closely related to Faraday’s Law. It is the ability of a coil or conductor to oppose the change in current flowing through it by generating an opposing EMF in itself. This effect occurs due to the coil’s own changing magnetic field linking with its turns.

When a current flows through a coil, it produces a magnetic field around it. If the current is steady (DC), the field remains constant, and there is no induced EMF. But if the current changes with time (as in AC or when switching DC on/off), the magnetic field changes, and this change induces a voltage within the same coil. This is called self-induced EMF.

Mathematical expression

The self-induced EMF (ε\varepsilonε) is given by:

ε=−L⋅dIdt\varepsilon = -L \cdot \frac{dI}{dt}ε=−L⋅dtdI​

Where:

• ε\varepsilonε = self-induced EMF (in volts)
• LLL = self-inductance (in henries, H)
• dIdt\frac{dI}{dt}dtdI​ = rate of change of current with time
• The negative sign comes from Lenz’s Law, indicating the EMF opposes the current change

Self-inductance

Self-inductance (L) is the property of a coil that determines how much EMF is induced for a given rate of change of current. A coil with higher self-inductance will oppose changes in current more strongly.

Factors affecting self-inductance:

1. Number of turns: More turns mean higher inductance.
2. Core material: Magnetic materials like iron increase inductance.
3. Area of coil: Larger area gives stronger magnetic field.
4. Length of coil: Shorter length increases the inductance.
5. Shape and spacing of turns: Compact winding increases the inductive effect.

Unit of inductance is henry (H). If a 1-ampere per second change in current produces 1 volt EMF, the coil has 1 henry of inductance.

Examples of self-induction

1. Inductors in circuits: Used to resist sudden changes in current and protect sensitive components.
2. Relay coils: When switching off, a back EMF is generated that may require protection using diodes.
3. Fluorescent tube starters: Rely on inductive kick from coils for proper ignition.
4. Electric chokes: Limit AC current using the self-inductive property.

Difference from mutual induction

• Self-induction happens in one coil due to its own changing current.
• Mutual induction occurs when one coil’s current induces EMF in another nearby coil.

Conclusion:

Self-induction is the process by which a coil resists a change in its own current by inducing an opposing EMF in itself. This phenomenon is a natural result of changing magnetic fields within the coil and is guided by Lenz’s Law. Self-induction is widely used in electronic components like inductors and plays an important role in managing current flow and energy storage in circuits.