Give one Important pratical application of photoelectric effect

Explanation

**Step-by-Step Solution:**

1. **Understanding the Photoelectric Effect**: The photoelectric effect is the phenomenon where electrons are emitted from a material (usually a metal) when it is exposed to light or electromagnetic radiation of sufficient energy.

2. **Identifying Practical Applications**: One of the most important practical applications of the photoelectric effect is in the functioning of automatic doors.

3. **Mechanism of Automatic Doors**: When a person approaches an automatic door, a light beam (often infrared) is emitted across the entrance. This light beam is continuously monitored by a sensor.

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