Optic Trees

General Board 1 : Optics is the study of interaction of light with matter. Properties of light such as reflection, refraction, diffraction, interference and polarization can be studied and understood when light interacts with materials.

This exhibit has eight segments. Each segment illustrates a certain property of light.

General Board 2 : Light is an electromagnetic wave that carries energy. Energy of a certain range stimulates the cells of our eye which the brain interprets as colour. This range is known as the visible light (spectrum). It forms a very small fraction of the entire range known as the electromagnetic spectrum.

Light is produced by the vibration of electric charges such as electrons. And, it propagates in a direction perpendicular to the direction of vibration. There are a number of naturally occurring materials whose electrons are constrained to vibrate in a specific direction. Such materials produce what is known as polarized light. We humans cannot detect polarized light without such materials. Several insects, however, use polarized light for navigation and communication.

Colour, brightness and polarization are the three key properties of light that we need in order to study ALL the optical phenomena that we come across.

Prism : Stand in front of the prism filled with a colourless liquid and look at the objects through it. Sunlight as well as the objects appear colourful. A prism bends different colours in sunlight by slightly different angles. On account of this, the colours can be easily resolved by the eye. This phenomenon is known as 'Refraction of light'.

Pinhole Camera : This is a closed box with a small hole on one face of the box and a screen on the face opposite it. Point the pinhole at a distant building or a tree. An inverted image of the object will be formed on the screen. The ray diagram here gives a rough, simplified idea of the image formation. Nautilus and hermit Crab have pinhole camera type eye in nature.

Kaleidoscope : Three long strips of plane mirrors are glued together to form an equilateral triangular prism. One end of the prism has a glass sphere. See through the other end. Whatever the object in front of the sphere is, you will see multiple, symmetrical images.

The glass sphere acts like a lens and forms the image of the object while the mirrors produce multiple images that are symmetric.

Polarized Light : The tube has a Polaroid sheet at its two ends. The sheet at one end is fixed. See through the other end and slowly rotate the Polaroid sheet placed there. You will notice that that the brightness of light gradually changes from a minimum to a maximum or vice versa.

Each Polaroid sheet is made up of identical long chain molecules aligned in a specific manner. Maximum light passes through the second Polaroid if its molecules are aligned parallel to those in the first Polaroid. It will be a minimum if its molecules are aligned perpendicular to those in the first Polaroid. For any other orientation, the light reaching us will have intermediate brightness.

Bees, dung beetles and several other insects are sensitive to polarized light.

Polaroid sheets are used to make and view 3D movies.

Periscope : Two plane mirrors are placed parallel to one another in this vertical pipe. Light entering through the opening in front of the top mirror reflects and propagates towards the mirror at the bottom. Upon reflecting at this surface, it emerges out of the opening in front of it. Looking through this opening, one can see the objects that are in front of and above one’s head.

Mudskipper fish and Ghost Crabs possess periscopic eyes.

Moire Pattern : Here we have two plates with holes made at regular intervals. One of the plates remains fixed. Rotate the other plate as you see through it. Different patterns emerge depending upon the extent to which the openings in the two plates overlap throughout the plate as seen from a particular position.

Colour Wheel : We have red, blue and green filters that can be rotated to overlap discs of one’s choice. The filter that absorbs green and blue components from white light transmits red. Likewise, the green filter absorbs blue and red; and the blue filter absorbs red and green. You can overlap two or all three filters to see the resulting colours. This is producing colours by removal of certain colours from white light.

Binocular : It is an optical device that improves the power of vision by magnifying the image. On account of this we perceive farther objects to be closer to us. It works like a twin telescope through which one can simultaneously see through them. Binoculars are described by numbers such as 10 X 50. It means that this binocular makes an object appear ten times larger and that the diameter of its objective lens is 50 mm.