Page 132 - Physics - XII

Result

1. The output voltage of the transformer across the secondary coil with respect to input voltage depends
N
on the turn ratio S .
N P
2. The output current of the transformer across the secondary coil with respect to input current depends
N
on the turn ratio S .
N P
3. Some loss of power between input and output coil of a transformer is observed.

Precautions

1. The improvised transformer may not have very high effi ciency otherwise it may get hot very soon.
2. Some special care should be taken while working with A.C. mains.
3. Before winding the turns on iron rod, it should be covered with a sheet of paper.
4. The zero error of voltmeter and ammeter should be taken into account.

PROJECT - 5

Aim
To investigate the dependence of the angle of deviation on the angle of incidence using a hollow prism
fi lled one by one, with diff erent transparent fl uids.

Apparatus and Materials Required

Hollow glass prism, a drawing board, white sheet of paper, drawing pins, scale, a pencil, a protractor, graph
papers, and liquids such as water, glycerine, turpentine oil

Principle/Theory
Consider the principal section ABC of the prism. A ray of light A
PQ (from air to glass) incident on the surface AB at an angle i is
refracted at an angle r along QR and fi nally emerges out along RS Q M D
as shown in Fig. 5.1. i r r′ e

The dotted lines in the fi gure represents the normal to the surfaces. R
The angle of incidence at the second surface AC (from glass to air) P S
is r′ and the angle of refraction or emergence be e. The angle of
deviation D is between the direction of incident ray PQ produced
forward and the direction of emergent ray RS produced backward. B C
From geometrical considerations, we have Fig. 5.1: Refraction of light through
A = r + r’ a prism

and D = ∠MQR + ∠MRQ = (i – r) + (e – r’)
D = i + e – A …(i)

For minimum deviation D , the light ray passes through the prism symmetrically, i.e. parallel to the base,
m
so that
D = D , i = e ⇒ r = r’
m
At the minimum deviation of position of the prism, we get the brightest image of an object.

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