Page 82 - Physics - XII

Graph and Calculations Y

Plot a graph between angle of incidence i and angle of 48 Scale used on:
deviation D, taking i along X-axis and D along Y-axis. 46 X- axis, 1 cm = ... degrees
The graph comes to be a curve as shown in Fig. 5.3. 44 Y- axis, 1 cm = ... degrees
Draw a tangent on the lowest point of the graph 42
parallel to X-axis. Note the angle of minimum 40
deviation D on Y-axis. Angle of deviation (in degree) D 38
m
The value of angle of minimum deviation from the 36
graph = D = _____ 34
m
Result 32
1. The graph between i and D indicates that as angle 20 30 40 50 60 70 X
of incidence i increases, angle of deviation D fi rst Angle of incidence (in degree) i
decreases, attains a minimum value D , and then
m
again starts increasing for further increase in angle Fig. 5.3: Graph between angle of incidence
and angle of deviation

of incidence.
2. The angle of minimum deviation, D = _____
m
Precautions

1. The pin should be fi xed vertical.
2. Encircle the pin pricks after they are removed.
3. Pins must be at a distance of about 8 to 10 cm.
4. The angle of incidence should lie between 30° to 60°.

5. The same angle of prism should be used for all the observations.
6. Draw the arrow to indicate the incidence, the refracted, and the emergent rays.
7. The curve should be free hand and smooth which should pass through as many points as possible.

Sources of Error

1. Measurement of the angle may be wrong.
2. Pin pricks may be thick.
3. The incident ray pins and emergent ray pins may not be along the same straight line.

EXPERIMENT - 6

Aim
To determine refractive index of a glass slab using a travelling microscope.

Apparatus and Materials Required
A glass slab, a marker, a travelling microscope, and lycopodium powder/chalk dust

Description of Apparatus
Travelling Microscope

A travelling microscope is an ordinary microscope (or a compound microscope) fi tted on a stand in such a
way that it can be made to travel in vertical as well as horizontal direction without disturbing its adjusted

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