G.O.A.

T PHYSICS
Wave Optics DPP #1
YDSE and Huygen’s Principle
1. The YDSE set-up is shown. On the lower slit a slab of thickness 0.1 mm
and refractive index 3/2 is placed λ = 5000 Å, d = 50×10 -4 cm, ϕ = 30°, D
= 2m. Find
a. Position of central maxima
b. Order of maxima at O and how many fringes will cross O if slab is
removed?
2. In double-slit experiment using light of wavelength 600 nm, the angular width of a fringe
formed on a distant screen is 0.1°. What is the spacing between the two slits?
3. White coherent light (400 nm-700 nm) is sent through the
slits of a YDSE, the separation between the slits is 0.5 mm
and the screen is 50 cm away from the slits. There is a
hole in the screen at a point 1 mm away (along the width
of the fringes) from the central line. Which wavelength
will be absent in the light coming from the hole?
4. In Young's double slit experiment, the two slits are kept 2
mm apart and the screen is positioned 140 cm away from the plane of the slits. The slits are
illuminated with light of wavelength 600 nm. Find the distance of the third bright fringes,
from the central maximum, in the interference pattern obtained on the screen. If the
wavelength of the incident light were changed to 480 nm, find out the shift in the position of
third bright fringe from the central maximum.
5. Laser light of wavelength 630 nm incident on a pair of slits produces an interference pattern
in which the bright fringes are separated by 7.2 mm. Calculate the wavelength of another
source of laser light which produces interference fringes separated by 8.1 mm using same
pair of slits.
6. In a Young's double slit experiment, the path difference at a certain point on the screen
between two interfering waves is 1/8th of the wavelength. The ratio of intensity at this point
to that at the centre of a bright fringe is close to
a. 0.80 c. 0.94
b. 0.74 d. 0.85
7. Two waves from two coherent sources S and S' superimpose at X as shown in the
figure. If X is a point on the second minima and SX – S'X is 4.5 cm. Calculate
the wavelength of the waves.
8. Monochromatic light of wavelength 5000 Aº is used in Y.D.S.E., with slit-width,
d = 1mm distance between screen and slits, D = 1m If intensity at the two slits
are, I1 = 4I0, I2 = I0 find
a. fringe width ẞ
b. distance of 5th minima from the central maxima on the screen
c. Intensity at y = 1/3 mm
d. Distance of the 1000th maxima e. Distance of the 5000th maxima
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9. In a Young's double slit experiment, a student observes 8 fringes in a certain segment of
screen when a monochromatic light of 600 nm wavelength is used. If the wavelength of light
is changed to 400 nm, then the number of fringes he would observe in the same region of the
screen is:
a. 8 b. 9 c. 12 d. 6
10.In Young's double slit experiment, if the separation between coherent sources is halved and
the distance of the screen from the coherent sources is doubled, then the fringe width
becomes :
a. half b. four times c. one-fourth d. double
11.In Young's double slit experiment, the fringe width is found to be 0.4 mm. If the whole
apparatus is immersed in water of refrative index 4/3 without disturbing the geometrical
arrangement, the new fringe width will be
a. 0.30 mm b. 0.40 mm c. 0.53 mm d. 450 microns
12.The intensity at the central maxima (O) in Young's
double slit experiment is I0. If the distance OP equals
one-third of the fringe width of the pattern, show that
the intensity at point P would be I0 / 4
13.In Young's experiment, the third bright band for light
of wavelength 6000 A coincides with the fourth
bright band from another source of light in the same
arrangement. Then the wavelength of second source is:
a. 3600 Å b. 4000 Å c. 5000 Å d. 4500 Å
14.The double slit experiment of Young has been shown in figure. is the
position of the first bright fringe on the right side and P is the 11th bright
fringe on the other side as measured from Q. If wavelength of the light
used is 6000 Å. S1B will be equal to 6×10-x m find x.
15.In Young's double-slit experiment, the intensity at a point where the path
difference is λ / 6 (being the wavelength of the light used) is I. If
I0denotes the maximum intensity. I / I0 is equal to:
a. √3/2 c. 3/4
b. 1/2 d. 1/√2
16.Spherical wave fronts shown in figure, strike a plane mirror. Reflected wave fronts
will be as shown in

d. c. b.
a.

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d. c.

b. a.

18.Plane wavefronts are incident on a spherical mirror as shown. The

a. b.

19.A point source of light is placed at origin, in air. The equation of wave front of the wave at
time t, emitted by source at t = 0 is (take refractive index of air as 1)
a. x+y+z= ct c. xy + yz + zx = c2t2
b. x2 + y2 + z2 = t2 d. x2 + y2 + z2 = c2t2
20.Figure shows a wavefront P passing through two systems A and B, and emerging as and then
as R. The system A and B could, respectively, be:
a. a prism and a convergent lens
b. a divergent lens and a prism
c. a convergent lens and a prism
d. a convergent lens and a divergent lens
21.A parallel beam of light passes from a medium of refractive index μ1
into a medium of refractive index μ2 as shown. The points P and Q lie
on the interface between the mediums. PP' is a wavefront in the first
medium and QQ’ is a wavefront in the second medium. The ratio
P'Q/PQ’ is equal to:
a.
b.

c.

d.
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