Ever wondered why certain balcony doors act as a mirror during nighttime?
Learn the concept of Reflecting Films and some other fun concepts with best-depicting sketches. You will learn the concept behind these films and their most interesting uses.
Let’s start.
ABOUT BALCONY DOORS
In places like Bangalore or Mumbai you can see that in most of the buildings they have used big sliding doors for balcony. Some of them may have used Reflecting films to prevent direct sunlight in the summertime. In this case, the door is working as a reflector of sunlight to save us from the heat.
People living in these places will also know that these doors act as a mirror during nighttime and we can see through the doors in the daytime. Ever wondered why this is happening?
This is because in day time light enters your door and reaches your eyes. When light inside of the room is much brighter than outside, light reflected from the door will enter your eyes and you will be able to see your reflection. while a person standing on the other side, say on the balcony, will be able to see you, because the light entering his\her eyes is the light from inside of the room.
This is the concept behind balcony doors. For more clarity refer to the image below.
If you want to learn what are Reflecting films. Continue Reading.
What are Reflecting Films?
Let us take the same example. In these balcony doors, a transparent thin film is deposited. Thin films are nothing but films whose thickness is comparable to the wavelength of light hitting the surface. light after hitting the film surface, following the laws of reflection, some of the light is reflected and some are refracted. The refracted light reaches the surface and it gets reflected and refracted again.
Know the Physics Side!
Interference- If we take two independent sources of light with constant phase difference and place them close to each other we get interference patterns.
Methods of obtaining Interference- 1) division of wavefront 2) division of amplitude. We will be considering the division of amplitude for our understanding.
What is optical path length?- you know that velocity is distance multiplied by time. path of light traveling through the medium will travel a lesser distance than a path of light traveling through air for the same amount of time. This is because light travels faster in the air. For more clarity refer to the image below.
so we can say that distance (rarer) will be equal to distance (medium) multiplied by the refractive index of the medium. The reflected light is changed only in direction while Refracted light changes both direction and speed of light due to the optical path length concept.
There is one more concept that you have to know to understand reflecting films. The light entering from rarer to denser medium changes path difference by lambda/2. While light entering from a denser medium enters a rarer medium there will be no path difference. This also is according to the concept of optical path difference that is explained above. If you are looking for a short derivation refer to the image below.
This was all about Reflecting Films and how they can be used on doors to save ourselves from the heat. Will come up with another topic next week. Happy Learning.
