How does the two-way mirror in the interrogation rooms work?

You must have seen two-way mirrors (double-sided mirrors) often mounted in interrogation rooms in movies. With a two-way mirror, the inner person cannot look outside but the outside person can observe the inner space. Why can two-dimensional mirrors be able to do so?

1. Why often have white smoke streaks in the sky after the plane flies over?
2. Why can airplanes fly in the sky?
3. Boiling eggs with a microwave may explode, why?

How is mirror mirror different from mirror?

Mirrors often have to go through a production process consisting of mirror coated, then coated with reflective materials such as silver, aluminum, tin or nickel.

How does the two-way mirror in the interrogation rooms work? Picture 1

The structure of the mirror usually consists of a transparent glass plate on the front, a copper layer that prevents oxidation of the metal and finally a reflective coating.

Light enters the glass and when it hits the metal surface, the light will reflect back. This is the reason why we can see the mirror image of ourselves when we look in the mirror.

Two-way mirrors are coated with such a metal but are thinner than conventional mirrors. The coating of reflective molecules covers only half of the total surface area of ​​the mirror and the other half gives light to pass through.

How does the two-way mirror in the interrogation rooms work? Picture 2 Principle of operation of two-sided mirrors.

Therefore, in the movies we often see the interrogation room always bright and the opposite room often to the darkest space possible to avoid light transmitted through the interrogation room.

Two-way mirrors operate on the principle of light intensity. If both glass surfaces have the same light intensity, the two-dimensional mirror is like a normal piece of glass.