10

I recently found out about the Magic Mirror. Both sides of the mirror look the same, and it appears to be dark, if looked at closely, like sunglasses (but lighter in colour) but looks like a normal mirror from afar.

  1. Why does it appear different from different locations? How exactly is it silvered? It behaves like glass (though much, much more reflective than refractive unlike normal glass) on both sides.
  2. If I turn the bulbs inside on, it displays the picture within and 'loses' its reflective nature entirely. How does that happen?

Please note that this is not a duplicate of this question.

psmears
  • 333
Stuti
  • 658
  • 4
    You can see this effect on any window in your house. From within your house at night, turn on bright lights in a room and look out the window. You will see your reflection. Turn the lights off and you will see outside. – foolishmuse Feb 26 '24 at 16:50
  • @foolishmuse Thanks, I've gotten that part now. – Stuti Feb 26 '24 at 16:55
  • There is another type of ‘magic’ mirror: the so-called “Chinese magic mirror”. I got to play with one long ago and it is impressive because it is basically a fairly thick piece of polished bronze with a detailed pattern impressed on the back face. When illuminated on the front (polished) face, the reflected light shows the pattern on the back (not illuminated) face. The one I played with was about 6 mm thick. The polished front surface did not visually display the pattern on the back surface. Very interesting mirror. – Ed V Feb 26 '24 at 23:34
  • The effect works very well in mirror clocks like this one (eBay), where the back of the mirror is completely dark until the digits turn on. You can get bathroom mirrors that work the same way – Chris H Feb 27 '24 at 09:51

1 Answers1

16

This is commonly called a "one way mirror", which really isn't a good name. It is really two way. It is a partially reflective, partially transmissive mirror that works the same either direction.

Suppose it is placed between two rooms, one bright, the other dark. Observers on both sides see a combination of reflection from their own room and and transmitted light from the other room.

In the bright room, there is very little transmitted light and a lot of reflected light. That is, the bright room observer sees their own reflection.

In the dark room, there is a lot of transmitted light and very little reflected light. The observer sees the transmitted light from the bright room.

In your case, there is a small compartment behind the mirror, and a light you can turn on or off. You can make that compartment be bright or dark.

With the light off, you see your reflection plus very little light transmitted through the mirror from the dark compartment.

With the light on, your reflection is still there. But so much light is transmitted through the mirror that all you see is transmitted light. A little like not hearing a whisper in a rock concert.

Greg Martin
  • 131
mmesser314
  • 38,487
  • 5
  • 49
  • 129