At an airport, a person is made to walk through the door way of a metal detector, for security reasons. If `she//he` is carrying anything made of metal, the metal detector emits a sound. On what principle does this detector work ?

Explanation

### Step-by-Step Solution:

1. **Understanding the Metal Detector's Function**:
- A metal detector is a device used to identify the presence of metal objects. At an airport, it is used for security checks to ensure that individuals are not carrying prohibited metal items.

2. **Principle of Operation**:
- The metal detector operates on the principle of **electromagnetic induction**. This principle states that a changing magnetic field can induce an electric current in a conductor.

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