Wave Optics- 1 Practice Questions - DPP for NEET

 Page 1


DIRECTIONS (Q.1-Q.20) : There are 20 multiple choice
questions. Each question has 4 choices (a), (b), (c) and (d), out
of which ONLY ONE choice is correct.
Q.1 The intensity ratio of two waves is 9 : 1. These waves
produce the event of interference. The ratio of maximum
to minimum intensity will be
(a) 1 : 9 (b) 9 : 1 (c) 1 : 4 (d) 4 : 1
Q.2 The equation of two light waves are y
1
 = 6cos wt,
y
2
 = 8cos(wt + f). The ratio of maximum to minimum
intensities produced by the superposition of these waves
will be
(a) 49 : 1 (b) 1 : 49
(c) 1 : 7 (d) 7 : 1
Q.3 In a Y oung’s double slit experiment, the separation between
the slits is 0.10 mm, the wavelength of light used is 600
nm and the interference pattern is observed on a screen
1.0 m away. Find the separation between the successive
bright fringes.
(a) 6.6 mm (b) 6.0 mm (c) 6 m (d) 6 cm.
Q.4 In Young’s double slit experiment the two slits are
illuminated by light of wavelength 5890 Å and the angular
separation between the fringes obtained on the screen is
0.2°. If the whole apparatus is immersed in water then the
angular fringe width will be, if the refractive index of water
is 4/3?
(a) 0.30° (b) 0.15° (c) 15° (d) 30°
Q.5 The intensities of two light sources are I and 9I respectively .
If the phase difference between the waves emitted by them
is p then the resultant intensity at the point of observation
will be –
(a) 3I (b) 4I (c) 10I (d) 82I
Page 2


DIRECTIONS (Q.1-Q.20) : There are 20 multiple choice
questions. Each question has 4 choices (a), (b), (c) and (d), out
of which ONLY ONE choice is correct.
Q.1 The intensity ratio of two waves is 9 : 1. These waves
produce the event of interference. The ratio of maximum
to minimum intensity will be
(a) 1 : 9 (b) 9 : 1 (c) 1 : 4 (d) 4 : 1
Q.2 The equation of two light waves are y
1
 = 6cos wt,
y
2
 = 8cos(wt + f). The ratio of maximum to minimum
intensities produced by the superposition of these waves
will be
(a) 49 : 1 (b) 1 : 49
(c) 1 : 7 (d) 7 : 1
Q.3 In a Y oung’s double slit experiment, the separation between
the slits is 0.10 mm, the wavelength of light used is 600
nm and the interference pattern is observed on a screen
1.0 m away. Find the separation between the successive
bright fringes.
(a) 6.6 mm (b) 6.0 mm (c) 6 m (d) 6 cm.
Q.4 In Young’s double slit experiment the two slits are
illuminated by light of wavelength 5890 Å and the angular
separation between the fringes obtained on the screen is
0.2°. If the whole apparatus is immersed in water then the
angular fringe width will be, if the refractive index of water
is 4/3?
(a) 0.30° (b) 0.15° (c) 15° (d) 30°
Q.5 The intensities of two light sources are I and 9I respectively .
If the phase difference between the waves emitted by them
is p then the resultant intensity at the point of observation
will be –
(a) 3I (b) 4I (c) 10I (d) 82I
2
DPP/ P 52
Q.6 In Fresnel’s biprism experiment the width of 10 fringes is
2cm which are formed at a distance of 2 meter from the
slit. If the wavelength of light is 5100Å then the distance
between two coherent sources will be
(a) 5.1 × 10
–4
 m (b) 5.1 × 10
4
 cm
(c) 5.1 × 10
–4
 mm (d) 10.1 × 10
–4
cm
Q.7 Two coherent sources of intensity ratio 1 : 4 produce an
interference pattern. The fringe visibility will be -
(a)1 (b) 0.8 (c) 0.4 (d) 0.6
Q.8 When a mica sheet (m = 1.6) of thickness 7 microns is
placed in the path of one of interfering beams in the biprism
experiment then the central fringe gets shifted at the
position of seventh bright fringe. The wavelength of light
used will be –
(a) 4000Å (b) 5000Å (c) 6000 Å (d) 7000Å
Q.9 In Young’s double slit experiment, the distance between
two slits is made three times then the fringe width will
become –
(a) 9 times (b) 1/9 times (c) 3 times (d) 1/3 times
Q.10 In the given diagram, CP represents a wavefront and AO &
BP, the corresponding two rays. Find the condition on q
for constructive interference at P between the ray BP and
reflected ray OP
Q 
O
C
A
P
B
R
d
q q
(a) cos q = 3l/2d (b) cos q = l/4d
(c) sec q – cosq = l/d (d) sec q – cosl = 4l/d
Q.11 In Young’s double slit experiment 10th order maximum is
obtained at the point of observation in the interference
pattern for l = 7000 Å. If the source is replaced by another
one of wavelength 5000 Å then the order of maximum at
the same point will be–
(a) 12 th (b) 14 th
(c) 16 th (d) 18 th
Q.12 In Y oung’s double slit experiment, white light is used. The
separation between the slits is b. The screen is at a distance
d (d > > b) from the slits. Some wavelengths are missing
exactly in front of one slit. One of these wavelengths is
(a)
2
b
=
6d
l (b)
2
2b
=
d
l (c)
2
b
=
3d
l (d)
2
2b
=
3d
l
Q.13In Fresnel’s biprism experiment distance of m
th
 bright
fringe from zeroth order fringe will be –
(a) (2m – 1)
D
2d
l
(b)
mD
d
l
(c)
md
D l
(d) (2m + 1)
D
2d
l
Q.14Consider interference between waves from two sources
of Intensites I & 4I. Find intensities at points where the
phase difference is 
2
p
.
(a)I (b) 5 I (c) 4 I (d) 3 I
Q.15 The width of one of the two slits in a Young’s double slit
experiment is double of the other slit. Assuming that the
amplitude of the light coming from a slit is proportional
to slit-width. Find the ratio of the maximum to the
minimum intensity in the interference pattern.
(a) 34 : 1 (b) 9 : 1 (c) 4 : 1 (d) 16 : 1
Q.16 The intensity of the light coming from one of the slits in a
young’s double slit experiment is double the intensity from
the other slit. Find the ratio of the maximum intensity to
the minimum intensity in the interference fringe pattern
observed.
(a) 9 : 1 (b) 34 : 1 (c) 4 : 1 (d) 16 : 1
Q.17 Two waves originating from source S
1
 and S
2
 having zero
phase difference and common wavelength l will show
completely destructive interference at a point P if
(S
1
 P – S
2
 P) is-
(a)5l (b)3l/4
(c)2l (d) 11l/2
Page 3


DIRECTIONS (Q.1-Q.20) : There are 20 multiple choice
questions. Each question has 4 choices (a), (b), (c) and (d), out
of which ONLY ONE choice is correct.
Q.1 The intensity ratio of two waves is 9 : 1. These waves
produce the event of interference. The ratio of maximum
to minimum intensity will be
(a) 1 : 9 (b) 9 : 1 (c) 1 : 4 (d) 4 : 1
Q.2 The equation of two light waves are y
1
 = 6cos wt,
y
2
 = 8cos(wt + f). The ratio of maximum to minimum
intensities produced by the superposition of these waves
will be
(a) 49 : 1 (b) 1 : 49
(c) 1 : 7 (d) 7 : 1
Q.3 In a Y oung’s double slit experiment, the separation between
the slits is 0.10 mm, the wavelength of light used is 600
nm and the interference pattern is observed on a screen
1.0 m away. Find the separation between the successive
bright fringes.
(a) 6.6 mm (b) 6.0 mm (c) 6 m (d) 6 cm.
Q.4 In Young’s double slit experiment the two slits are
illuminated by light of wavelength 5890 Å and the angular
separation between the fringes obtained on the screen is
0.2°. If the whole apparatus is immersed in water then the
angular fringe width will be, if the refractive index of water
is 4/3?
(a) 0.30° (b) 0.15° (c) 15° (d) 30°
Q.5 The intensities of two light sources are I and 9I respectively .
If the phase difference between the waves emitted by them
is p then the resultant intensity at the point of observation
will be –
(a) 3I (b) 4I (c) 10I (d) 82I
2
DPP/ P 52
Q.6 In Fresnel’s biprism experiment the width of 10 fringes is
2cm which are formed at a distance of 2 meter from the
slit. If the wavelength of light is 5100Å then the distance
between two coherent sources will be
(a) 5.1 × 10
–4
 m (b) 5.1 × 10
4
 cm
(c) 5.1 × 10
–4
 mm (d) 10.1 × 10
–4
cm
Q.7 Two coherent sources of intensity ratio 1 : 4 produce an
interference pattern. The fringe visibility will be -
(a)1 (b) 0.8 (c) 0.4 (d) 0.6
Q.8 When a mica sheet (m = 1.6) of thickness 7 microns is
placed in the path of one of interfering beams in the biprism
experiment then the central fringe gets shifted at the
position of seventh bright fringe. The wavelength of light
used will be –
(a) 4000Å (b) 5000Å (c) 6000 Å (d) 7000Å
Q.9 In Young’s double slit experiment, the distance between
two slits is made three times then the fringe width will
become –
(a) 9 times (b) 1/9 times (c) 3 times (d) 1/3 times
Q.10 In the given diagram, CP represents a wavefront and AO &
BP, the corresponding two rays. Find the condition on q
for constructive interference at P between the ray BP and
reflected ray OP
Q 
O
C
A
P
B
R
d
q q
(a) cos q = 3l/2d (b) cos q = l/4d
(c) sec q – cosq = l/d (d) sec q – cosl = 4l/d
Q.11 In Young’s double slit experiment 10th order maximum is
obtained at the point of observation in the interference
pattern for l = 7000 Å. If the source is replaced by another
one of wavelength 5000 Å then the order of maximum at
the same point will be–
(a) 12 th (b) 14 th
(c) 16 th (d) 18 th
Q.12 In Y oung’s double slit experiment, white light is used. The
separation between the slits is b. The screen is at a distance
d (d > > b) from the slits. Some wavelengths are missing
exactly in front of one slit. One of these wavelengths is
(a)
2
b
=
6d
l (b)
2
2b
=
d
l (c)
2
b
=
3d
l (d)
2
2b
=
3d
l
Q.13In Fresnel’s biprism experiment distance of m
th
 bright
fringe from zeroth order fringe will be –
(a) (2m – 1)
D
2d
l
(b)
mD
d
l
(c)
md
D l
(d) (2m + 1)
D
2d
l
Q.14Consider interference between waves from two sources
of Intensites I & 4I. Find intensities at points where the
phase difference is 
2
p
.
(a)I (b) 5 I (c) 4 I (d) 3 I
Q.15 The width of one of the two slits in a Young’s double slit
experiment is double of the other slit. Assuming that the
amplitude of the light coming from a slit is proportional
to slit-width. Find the ratio of the maximum to the
minimum intensity in the interference pattern.
(a) 34 : 1 (b) 9 : 1 (c) 4 : 1 (d) 16 : 1
Q.16 The intensity of the light coming from one of the slits in a
young’s double slit experiment is double the intensity from
the other slit. Find the ratio of the maximum intensity to
the minimum intensity in the interference fringe pattern
observed.
(a) 9 : 1 (b) 34 : 1 (c) 4 : 1 (d) 16 : 1
Q.17 Two waves originating from source S
1
 and S
2
 having zero
phase difference and common wavelength l will show
completely destructive interference at a point P if
(S
1
 P – S
2
 P) is-
(a)5l (b)3l/4
(c)2l (d) 11l/2
DPP/ P 52
3
Q.18In an interference pattern, at a point we observe the 16
th
order maximum for l
1
= 6000Å. What order will be visible
here if the source is replaced by light of wavelength ?
l
2
 = 4800 Å.
(a) 40 (b) 20
(c) 10 (d) 80
Q.19In Young’s experiment the wavelength of red light is
7.5 × 10
–5
 cm. and that of blue light 5.0 × 10
–5
  cm. The
value of n for which (n + 1)
th
  blue bright band coincides
with n
th
 red bright band is-
(a)8 (b)4
(c)2 (d)1
Q.20 In Y oung’s double slit experiment, carried out with light of
wavelength l = 5000Å, the distance between the slits is
0.2mm and the screen is at 200 cm from the slits. The
central maximum is at x = 0. The third maximum will be at
x equal to.
(a) 1.67 cm (b) 1.5 cm
(c) 0.5 cm (d) 5.0 cm
DIRECTIONS (Q.21-Q.23) : In the following questions,
more than one of the answers  given are correct. Select the
correct answers and mark it according to the following
codes:
Codes :
(a) 1, 2 and 3 are correct (b) 1 and 2 are correct
(c) 2 and 4 are correct (d) 1 and 3 are correct
Q.21 The Y oung’s double slit experiment, the ratio of intensities
of bright and dark fringes is 9. This means that
(1) The intensities of individual sources are 5 and 4 units
respectively
(2) The intensities of individual sources are 4 and 1 units
respectively
(3) The ratio of the their amplitudes is 3
(4) The ratio of their amplitude is 2
Q.22In an experiment similar to Young’s experiment,
interference is observed using waves associated with
electrons. The electrons are being produced in an electron
gun. In order to decrease the fringe width
(1) electron gun voltage be increased.
(2) the slits be moved away from each other.
(3) the screen be moved closer to interfering slits.
(4) electron gun voltage be decreased.
Q.23 Interference fringes were produced in Young’s double slit
experiment using light of wave length 5000 Å. When a film
of material 2.5 × 10
–3
 cm thick was placed over one of the
slits, the fringe pettern shifted by a distance equal to 20
fringe width. The refractive index of the material of the
film cannot be
(1) 1.25 (2) 1.33
(3) 1.5 (4) 1.4
DIRECTIONS (Q.24-Q.26) : Read the passage given below
and answer the questions that follows :
In a Y oung’s double slit experiment a monochromatic light whose
wavelength is l strikes on the slits, separated by distance d, as
shown in the figure. Refractive index of the medium between
slits and screen varies with time t as n = n
0
 + kt. Here n
0
 and k
are positive constants. Position of any point P on screen is
measure by its y-coordinate as shown.
P
y 
O 
d 
D
S
2
 
f
l
 n = (n + kt)
0
1
 
AIR
Q.24 The y co-ordinate of central maxima at any time t is
(a)
0
sin D
n kt
f
+
(b)
0
cos D
n kt
f
+
(c)
2
0
sin
()
D
n kt
f
+
(d)
2
0
cos
()
D
n kt
f
+
Page 4


DIRECTIONS (Q.1-Q.20) : There are 20 multiple choice
questions. Each question has 4 choices (a), (b), (c) and (d), out
of which ONLY ONE choice is correct.
Q.1 The intensity ratio of two waves is 9 : 1. These waves
produce the event of interference. The ratio of maximum
to minimum intensity will be
(a) 1 : 9 (b) 9 : 1 (c) 1 : 4 (d) 4 : 1
Q.2 The equation of two light waves are y
1
 = 6cos wt,
y
2
 = 8cos(wt + f). The ratio of maximum to minimum
intensities produced by the superposition of these waves
will be
(a) 49 : 1 (b) 1 : 49
(c) 1 : 7 (d) 7 : 1
Q.3 In a Y oung’s double slit experiment, the separation between
the slits is 0.10 mm, the wavelength of light used is 600
nm and the interference pattern is observed on a screen
1.0 m away. Find the separation between the successive
bright fringes.
(a) 6.6 mm (b) 6.0 mm (c) 6 m (d) 6 cm.
Q.4 In Young’s double slit experiment the two slits are
illuminated by light of wavelength 5890 Å and the angular
separation between the fringes obtained on the screen is
0.2°. If the whole apparatus is immersed in water then the
angular fringe width will be, if the refractive index of water
is 4/3?
(a) 0.30° (b) 0.15° (c) 15° (d) 30°
Q.5 The intensities of two light sources are I and 9I respectively .
If the phase difference between the waves emitted by them
is p then the resultant intensity at the point of observation
will be –
(a) 3I (b) 4I (c) 10I (d) 82I
2
DPP/ P 52
Q.6 In Fresnel’s biprism experiment the width of 10 fringes is
2cm which are formed at a distance of 2 meter from the
slit. If the wavelength of light is 5100Å then the distance
between two coherent sources will be
(a) 5.1 × 10
–4
 m (b) 5.1 × 10
4
 cm
(c) 5.1 × 10
–4
 mm (d) 10.1 × 10
–4
cm
Q.7 Two coherent sources of intensity ratio 1 : 4 produce an
interference pattern. The fringe visibility will be -
(a)1 (b) 0.8 (c) 0.4 (d) 0.6
Q.8 When a mica sheet (m = 1.6) of thickness 7 microns is
placed in the path of one of interfering beams in the biprism
experiment then the central fringe gets shifted at the
position of seventh bright fringe. The wavelength of light
used will be –
(a) 4000Å (b) 5000Å (c) 6000 Å (d) 7000Å
Q.9 In Young’s double slit experiment, the distance between
two slits is made three times then the fringe width will
become –
(a) 9 times (b) 1/9 times (c) 3 times (d) 1/3 times
Q.10 In the given diagram, CP represents a wavefront and AO &
BP, the corresponding two rays. Find the condition on q
for constructive interference at P between the ray BP and
reflected ray OP
Q 
O
C
A
P
B
R
d
q q
(a) cos q = 3l/2d (b) cos q = l/4d
(c) sec q – cosq = l/d (d) sec q – cosl = 4l/d
Q.11 In Young’s double slit experiment 10th order maximum is
obtained at the point of observation in the interference
pattern for l = 7000 Å. If the source is replaced by another
one of wavelength 5000 Å then the order of maximum at
the same point will be–
(a) 12 th (b) 14 th
(c) 16 th (d) 18 th
Q.12 In Y oung’s double slit experiment, white light is used. The
separation between the slits is b. The screen is at a distance
d (d > > b) from the slits. Some wavelengths are missing
exactly in front of one slit. One of these wavelengths is
(a)
2
b
=
6d
l (b)
2
2b
=
d
l (c)
2
b
=
3d
l (d)
2
2b
=
3d
l
Q.13In Fresnel’s biprism experiment distance of m
th
 bright
fringe from zeroth order fringe will be –
(a) (2m – 1)
D
2d
l
(b)
mD
d
l
(c)
md
D l
(d) (2m + 1)
D
2d
l
Q.14Consider interference between waves from two sources
of Intensites I & 4I. Find intensities at points where the
phase difference is 
2
p
.
(a)I (b) 5 I (c) 4 I (d) 3 I
Q.15 The width of one of the two slits in a Young’s double slit
experiment is double of the other slit. Assuming that the
amplitude of the light coming from a slit is proportional
to slit-width. Find the ratio of the maximum to the
minimum intensity in the interference pattern.
(a) 34 : 1 (b) 9 : 1 (c) 4 : 1 (d) 16 : 1
Q.16 The intensity of the light coming from one of the slits in a
young’s double slit experiment is double the intensity from
the other slit. Find the ratio of the maximum intensity to
the minimum intensity in the interference fringe pattern
observed.
(a) 9 : 1 (b) 34 : 1 (c) 4 : 1 (d) 16 : 1
Q.17 Two waves originating from source S
1
 and S
2
 having zero
phase difference and common wavelength l will show
completely destructive interference at a point P if
(S
1
 P – S
2
 P) is-
(a)5l (b)3l/4
(c)2l (d) 11l/2
DPP/ P 52
3
Q.18In an interference pattern, at a point we observe the 16
th
order maximum for l
1
= 6000Å. What order will be visible
here if the source is replaced by light of wavelength ?
l
2
 = 4800 Å.
(a) 40 (b) 20
(c) 10 (d) 80
Q.19In Young’s experiment the wavelength of red light is
7.5 × 10
–5
 cm. and that of blue light 5.0 × 10
–5
  cm. The
value of n for which (n + 1)
th
  blue bright band coincides
with n
th
 red bright band is-
(a)8 (b)4
(c)2 (d)1
Q.20 In Y oung’s double slit experiment, carried out with light of
wavelength l = 5000Å, the distance between the slits is
0.2mm and the screen is at 200 cm from the slits. The
central maximum is at x = 0. The third maximum will be at
x equal to.
(a) 1.67 cm (b) 1.5 cm
(c) 0.5 cm (d) 5.0 cm
DIRECTIONS (Q.21-Q.23) : In the following questions,
more than one of the answers  given are correct. Select the
correct answers and mark it according to the following
codes:
Codes :
(a) 1, 2 and 3 are correct (b) 1 and 2 are correct
(c) 2 and 4 are correct (d) 1 and 3 are correct
Q.21 The Y oung’s double slit experiment, the ratio of intensities
of bright and dark fringes is 9. This means that
(1) The intensities of individual sources are 5 and 4 units
respectively
(2) The intensities of individual sources are 4 and 1 units
respectively
(3) The ratio of the their amplitudes is 3
(4) The ratio of their amplitude is 2
Q.22In an experiment similar to Young’s experiment,
interference is observed using waves associated with
electrons. The electrons are being produced in an electron
gun. In order to decrease the fringe width
(1) electron gun voltage be increased.
(2) the slits be moved away from each other.
(3) the screen be moved closer to interfering slits.
(4) electron gun voltage be decreased.
Q.23 Interference fringes were produced in Young’s double slit
experiment using light of wave length 5000 Å. When a film
of material 2.5 × 10
–3
 cm thick was placed over one of the
slits, the fringe pettern shifted by a distance equal to 20
fringe width. The refractive index of the material of the
film cannot be
(1) 1.25 (2) 1.33
(3) 1.5 (4) 1.4
DIRECTIONS (Q.24-Q.26) : Read the passage given below
and answer the questions that follows :
In a Y oung’s double slit experiment a monochromatic light whose
wavelength is l strikes on the slits, separated by distance d, as
shown in the figure. Refractive index of the medium between
slits and screen varies with time t as n = n
0
 + kt. Here n
0
 and k
are positive constants. Position of any point P on screen is
measure by its y-coordinate as shown.
P
y 
O 
d 
D
S
2
 
f
l
 n = (n + kt)
0
1
 
AIR
Q.24 The y co-ordinate of central maxima at any time t is
(a)
0
sin D
n kt
f
+
(b)
0
cos D
n kt
f
+
(c)
2
0
sin
()
D
n kt
f
+
(d)
2
0
cos
()
D
n kt
f
+
4
DPP/ P 52
Q.25 The velocity of central maxima at any time t as a function
of time t is
(a)
2
0
–2 sin
()
kD
n kt
f
+
(b) 
2
0
– sin
()
kD
n kt
f
+
(c)
0
–2 sin
()
kD
n kt
f
+
(d)
0
– sin
()
kD
n kt
f
+
Q.26 If a glass plate of small thickness b is placed in front of S
1
.
How should its refractive index vary with time so that
central maxima is formed at O.
(a)
0
2 sin d
n kt
b
f
++ (b)
0
2 sin
–
d
n kt
b
f
+
(c)
0
sin
–
d
n kt
b
f
+ (d)
0
sin d
n kt
b
f
++
DIRECTIONS (Q. 27-Q.29) : Each of these questions contains
two statements: Statement-1 (Assertion) and Statement-2
(Reason). Each of these questions has four alternative choices,
only one of which is the correct answer. You have to select the
correct choice.
(a) Statement-1 is True, Statement-2 is True; Statement-2 is a
correct explanation for  Statement-1.
(b) Statement-1 is True, Statement-2 is True; Statement-2 is
NOT a correct explanation for Statement-1.
(c) Statement -1 is False, Statement-2 is True.
(d) Statement -1 is True, Statement-2 is False.
Q.27 Statement-1 : No interference pattern is detected when
two coherent sources are infinitely close to each other.
Statement-2 : The fringe width is directly proportional to
the distance between the two slits.
Q.28 Statement-1 : In Y oung’s experiment, the fringe width for
dark fringes is same as that for white fringes.
Statement-2 : In Y oung’s double slit experiment performed
with a source of white light, only black and bright fringes
are observed.
Q.29 Statement-1 : In Y oung’s double slit experiment, the fringes
become indistinct if one of the slits is covered with
cellophane paper.
Statement-2 : The cellophane paper decreases the
wavelength of light.