Among the various properties of light, reflection and refraction are two of the most important aspects. In this chapter, you are going to study in detail about these two properties with the help of specific situations and conditions.
Out of them, the experiment for refraction through glass slab is the most vital. Before delving deeper into this experiment and its conclusions, students should have prior knowledge of its concept. Having clarity on the two properties of light is crucial to gain a stronghold on the advanced concepts.
So, let us understand these properties first.
Reflection and Refraction
Look at the image below to understand refraction through glass slab -
The image here shows both the reflected and refracted rays. It presents the rays during reflection and also during refraction of light through the glass slab. As the name implies, a reflected ray is the one which deviates at the same angle in which it falls on a surface.
On the other hand, during refraction through glass slab, the ray passes through this surface. Once it has passed this surface, it deviates at an angle different from the one at which it fell.
There are a few common phenomena which show both reflection and refraction of light through a glass slab. Herein, students have to be clear about both terms and also angles at which a ray is incident on a surface.
Law of Reflection
Students should note here that during reflection, a light ray travels in the same medium. In simple words, the ray is incident and reflected in a common medium, say air. However, the observation of refraction of light indicates that there is a change in angle.
It means, during refraction, light rays change their path. In other words, they deviate from their angle of incidence when they change their medium of travel.
This is where the glass slab experiment must be understood by students since it proves these phenomena discussed above. However, before shifting to the experiment, you should know about the laws of reflection, which states -
‘Reflected ray, normal and incident ray lie on a common plane.’
‘Ratio of sine of an incident ray to the sine of reflected ray is a constant.’
sine i/ sine r = k
Herein, i is angle of incidence, r is angle of reflection, and k is a constant.
Refraction Through A Glass Slab
To prove the property of light, we perform an experiment that shows refraction through a rectangular glass slab. To conduct this experiment, you will need -
Scale and protractor
The steps in this experiment to explain refraction through a rectangular glass slab are as follows -
Fix the white sheet on a drawing board with thumb pins.
Outline a glass slab and label it ABCD.
Draw a perpendicular on one side and label it as normal EP on side AB.
Draw an angle 30° and fix two pins 3 or 4 cms apart on this line.
See through the glass slab and place these other two pins on the other side of this slab. Make sure that all four pins are in a straight line.
Mark those four points with a circle.
Remove the glass slab and join the dots.
Therefore, the glass slab experiment observations reveal that on traveling of light rays from one medium to another, refraction takes place.
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1. What is reflection?
When a light ray falls on a surface at an angle, it reflects at the same angle. This phenomenon is called reflection.
2. How is it different from refraction?
Reflection differs from refraction in a way that in the latter, incident rays deviate at a different angle after being refracted. Whereas, the former does not change the angle and remains in the same medium.
3. What is the law of reflection?
The law of reflection, as stated by Snell, is that the ratio of sine of angle of incidence and angle of reflection is a constant.