14/01/2017
Fun with Science:
No.1: Make Objects Seemingly Disappear-
Basic Principle- Refraction is when light changes direction and speed as it passes from one object to another. Only visible objects reflect light. The velocity of light, C, in a vacuum is 2.99793 x (10 to the power 10) cm/sec. Light cannot travel faster than this, but if it travels through a substance, its velocity will decrease. Note that from the equation --
C = λf
The frequency of vibration,f, remains constant when the light passes through a substance. Thus, if the velocity, C, is reduced on passage through a substance, the wavelength, λ, must also decrease.
We here define refractive index, n, of a material or substance as the ratio of the speed of light in a vacuum, C, to the speed of light in a material through which it passes, Cm.
n = C/Cm
Note that the value of refractive index will always be greater than 1.0, since Cm can never be greater than C. In general, Cm depends on the density of the material, with Cm decreasing with increasing density. Thus, higher density materials will have higher refractive indices.
When two materials with similar reflective properties come into contact, light will pass through both the materials at the same speed, rendering the other material invisible.
Experiment:
Stuff you need: PYREX Or VEGETABLE OIL (Refractive Index- 1.147), BEAKERS (3 Nos.), TEST TUBES (4 Nos.), WATER (Refractive Index- 1.333).
Preparation: Each of the above Beakers pour Pyrex/ Vegetable Oil (Beaker No.1), Water (Beaker No.2), and half quantity Water & half quantity Pyrex/ Vegetable Oil (Beaker No.3).
For the above four Test Tubes do the following:
Test Tube No.1: Make both ends open.
Test Tube No.2: Fill water.
Test Tube No.3: Fill Pyrex/ Vegetable Oil.
Test Tube No.4: Fill-up half quantity water and half quantity Pyrex/ Vegetable Oil.
Tests: Immerge each of the Test Tube in turn inside the above Beakers.
Observations:
Test Tube No.1: For all the above three Beakers it is invisible.
Test Tube No.2: It is invisible inside the Beaker containing water (Beaker No2). Also, in the Beaker No.3 where half quantity water and half quantity Pyrex/ Vegetable Oil, it is visible in Pyrex/ Vegetable Oil, but not visible inside water. It is visible in Beaker No.1 containing Pyrex/ Vegetable Oil.
Test Tube No.3: It is invisible inside the Beaker containing Pyrex/ Vegetable Oil (Beaker No.1)l. Also, in the Beaker No.3 where half quantity water and half quantity Pyrex/ Vegetable Oil, it is visible in water, but not visible inside Pyrex/ Vegetable Oil. For Beaker No.2 where water is there it is visible.
Test Tube No.4: Gage what may happen.
