Manual

14
Dispersion of Colors: Allow a wide beam of light to be incident on one face of the equilateral prism.
On a white screen, observe the emergent spectrum for different angles of deviation (from minimum
deviation to near-internal reflection).
•
What difference is there between the spectra obtained at minimum deviation and near-internal
reflection? (Hint: How many colors are seen in each case?) Why?
•
Would you say that µ is the same r all colors? If not, arrange the colors in order of increasing µ.
•
A prism is just a parallel-slab cut diagonally. Why, then, is there no dispersion of colors in a slab?
Rain-drops are shaped like prisms. Hence, they also disperse colors and form colorful rainbows.
In the above experiment, study the effect of placing filters of different colors, along with the slit-
former.
Focus - Convex Lens: Allow parallel rays to fall on the convex lens parallel to its axis of symmetry.
These rays meet (after refraction) at the FOCUS. The distance, OF, is the focal length (f) of the lens.
Place a diverging lens in front of the slits so that diverging rays fall on the convex lens.
The focal length (ignoring signs) is then given by
uvf
111
+=
Where, f = focal length of the convex lens
v = OV where V is the point the rays meet
u = OU where U is the point from which the incident rays appear to be diverging from
O
F
Fig.