Define mutual inductance.

Explanation

**Step-by-Step Text Solution:**

1. **Understanding Mutual Inductance**: Mutual inductance is a phenomenon that occurs when the magnetic field created by one coil induces a voltage in another nearby coil. This interaction is fundamental in electromagnetic theory and is essential for the operation of many electrical devices.

2. **Visualizing the Coils**: Imagine two coils placed close to each other. When an electric current flows through the first coil, it generates a magnetic field around it. This magnetic field can extend to the second coil.

3. **Induction of Voltage**: The changing magnetic field from the first coil induces a voltage in the second coil. This induced voltage is a result of the interaction between the magnetic fields of the two coils.

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