AIM: To verify the laws of refraction using a glass slab.
APPARATUS: Glass slab, drawing board, drawing pins, sheets of paper, cello tape, protractor and a pencil.
PRINCIPLE: When a ray of light passes from one medium to the other, its velocity as well as the path change due to a phenomenon called refraction. When the ray of light passes from a denser to a rarer medium, it travels away from the normal and when it passes the rarer to the denser medium, it bends towards the normal.
LAWS OF REFRACTION:
1. The incident ray, the refracted ray and the normal lie in the same plane at the point of incidence.
2. The ratio of the sin of angle of incidence to the sin of angle of refraction is a constant quantity called refractive index
1. Fix a sheet of paper on the drawing board with cello tape.
2. Place the glass slab horizontally and draw its boundary.
3. Remove the glass slab.
4. Mark a point O as shown in the figure and draw the normal NON’ through O.
5. Draw a line AO such that the angle AON is 30 degrees.
6. Place the glass slab back to its original position.
7. Fix two pins along the line AO.
8. Looking through the other side of the slab, fix two more pins such that these two pins and the images of the previous two pins seem to be in a straight line.
9. Remove the pins and the glass slab and draw the refracted and the emergent rays OB and BC.
10. Measure the angle BON’ that is the angle of refraction.
11. Take four more observations with different values of angles of incidence each time.
1. The glass slab must be correctly placed on the out line for all the observations.
2. Pins must be vertical.
3. While viewing through the other end of the glass slab, the feet of the pins must be adjusted to form a straight line and not the heads.
1. Since the incident ray, the refracted ray and the normal lie in the same plane that is the plane of paper at the point of incidence, the first law is verified.
2. The ratio of sin of angle of incidence to the sin of angle of refraction is a constant called the refractive index of the glass with respect to the air and its value is found to be _____