(ii) express the velocity of propagation in terms of
the amplitudes of the oscillating electric and
magnetic elds.
(b) How do you show that the e.m. wave carries
energy and momentum?
- Two wavelengths of sodium light 590 nm and
596 nm are used, in turn to study the di raction
taking place at a single slit of aperture 2 u 10 –4 m.
e distance between the slit and the screen is
1.5 m. Calculate the separation between the
positions of the rst maxima of the di raction
pattern obtained in the two cases.
- (a) Draw a ray diagram showing the formation of
image by a re ecting telescope.
(b) Write two advantages of a re ecting telescope
over a refracting telescope.
- (a) Good quality sun-glasses made of polaroids
are preferred over ordinary coloured glasses.
Justifying your answer.
(b) Two polaroids P 1 and P 2 are placed in crossed
postions. A third polaroid P 3 is kept between
P 1 and P 2 such that pass axis of P 3 is parallel to
that of P 1. How would the intensity of light (I 2 )
transmitted through P 2 vary as P 3 is rotated?
Draw a plot of intensity ‘I 2 ” versus the angle ‘q’
between pass axes of P 1 and P 3.
SECTION D
- (a) Derive the mathematical relation between
refractive indices n 1 and n 2 of two media and
radius of curvature R for refraction at a convex
spherical surface. Consider the object to be a
point source lying on the principle axis in rarer
medium of refractive index n 1 and a real image
formed in the denser medium of refractive
index n 2. Hence, derive lens maker’s formula.
(b) Light from a point source in air falls on a convex
spherical glass surface of refractive index 1.5 and
radius of curvature 20 cm. e distance of light
source from the glass surface is 100 cm. At what
position is the image formed?
OR
(a) A monochromatic source of light of wavelength
O illuminates a narrow slit of width d to produce
a di raction pattern on the screen. Obtain the
conditions when secondary wavelets originating
from the slit interfere to produce maxima and
minima on the screen.
(b) How would the di raction pattern be a ected
when
(i) the width of the slit is decreased?
(ii) the monochromatic source of light is replaced
by white light?
- (a) A ray of monochromatic light is incident on
one of the faces of an equilateral triangular
prism of refracting angle A. Trace the path of
ray passing through the prism. Hence, derive
an expression for the refractive index of the
material of the prism in terms of the angle of
minimum deviation and its refracting angle.
(b) ree light rays red (R), green (G) and blue (B)
are incident on the right angled prism abc at
face ab. e refractive indices of the material of
the prism for red, green and blue wavelengths
are respectively 1.39, 1.44 and 1.47. Trace the
paths of these rays reasoning out the di erence
in their behaviour.
a
bc
B
G
R
45°
OR
In Young’s double slit experiment, deduce
the condition for (i) constructive, and
(ii) destructive interference at a point on the screen.
Draw a graph showing variation of intensity in
the interference pattern against position ‘x’ on the
screen.
- Draw a ray diagram to show the working of a
compound microscope. Deduce an expression for
the total magni cation when the nal image is
formed at the near point.
In a compound microscope, an object is placed at a
distance of 1.5 cm from the objective of focal length
1.25 cm. If the eye piece has a focal length of 5 cm
and the nal image is formed at the near point,
estimate the magnifying power of the microscope.
OR
(a) Describe brie y how an unpolarised light get
linearly polarized when it passes through a
polaroid.
(b) ree identical polaroid sheets P 1 , P 2 and P 3 are
oriented so that the pass axis of P 2 and P 3 are
inclined at angle of 60q and 90q respectively with
