Question

What is the difference between self induction and mutual induction?

Answer 1

Self-induction and mutual induction are both concepts related to electromagnetic induction, but they occur in different situations. Here's how they differ:

### 1. **Self-Induction:**
   - **Definition:** Self-induction occurs when a changing current in a coil (or any conductor) induces an electromotive force (EMF) in the same coil.
   - **How it happens:** When the current in a coil changes (either increases or decreases), it creates a changing magnetic field around the coil. This changing magnetic field then induces an EMF (voltage) in the same coil, opposing the change in current (according to Lenz’s Law).
   - **Formula:** The induced EMF (or voltage) is proportional to the rate of change of current and the inductance of the coil:
     \[
     \text{EMF} = -L \frac{dI}{dt}
     \]
     Where:
     - \( L \) is the inductance of the coil.
     - \( \frac{dI}{dt} \) is the rate of change of current.

### 2. **Mutual Induction:**
   - **Definition:** Mutual induction occurs when a changing current in one coil induces an EMF in a nearby coil.
   - **How it happens:** When the current in the first coil changes, it creates a changing magnetic field around it. If there is a second coil placed within this changing magnetic field, an EMF is induced in the second coil. This is called mutual induction.
   - **Formula:** The induced EMF in the second coil is proportional to the rate of change of current in the first coil and the mutual inductance between the two coils:
     \[
     \text{EMF}_2 = -M \frac{dI_1}{dt}
     \]
     Where:
     - \( M \) is the mutual inductance between the coils.
     - \( \frac{dI_1}{dt} \) is the rate of change of current in the first coil.

### Key Differences:
- **Self-Induction:** The coil induces EMF in itself due to its own changing current.
- **Mutual Induction:** One coil induces EMF in a nearby coil due to the changing current in the first coil.

In summary:
- **Self-induction** is like a coil trying to resist changes in its own current.
- **Mutual induction** is when one coil influences another by creating a changing magnetic field.

Both involve magnetic fields, but in self-induction, it’s the coil’s own current that changes, while in mutual induction, it’s the current of a nearby coil that causes the effect.