Wave Optics - 2 Practice Questions - DPP for NEET

 Page 1


DIRECTIONS (Q.1-Q.22) : There are 22 multiple choice
questions. Each question has 4 choices (a), (b), (c) and (d), out
of which ONLY ONE choice is correct.
Q.1 The first diffraction minima due to a single slit diffraction
is at q = 30° for a light of wavelength 5000Å. The width of
the slit is-
(a) 5 × 10
–5
 cm (b) 1.0 × 10
–4
 cm
(c) 2.5 × 10
–5
 cm (d) 1.25 × 10
–5
 cm
Q.2 Two spectral line of sodium D
1
 & D
2
 have wavelengths of
approximately 5890Å and 5896Å. A sodium lamp sends
incident plane wave on to a slit of width 2 micrometre. A
screen is located  at 2m from the slit. Find the spacing
between the first maxima of two sodium lines as measured
on the screen.
(a) 10
–4
 m (b) 9 × 10
–4
 m
(c) 9 × 10
4
 m (d) None
Q.3 Width of slit is 0.3mm. Fraunhoffer diffraction is observed
in focus plane of lense of a lense of focal length 1 m. If
third minima is at 5 mm distance from central maxima,
then wavelength of light is-
(a) 7000Å (b) 6500Å (c) 6000Å (d) 5000Å
Q.4 When a wave of  wavelength 0.2 cm is made incident
normally on a slit of width 0.004m, then the semi-angular
width of central maximum of diffraction pattern will be-
(a) 60° (b) 30° (c) 90° (d) 0°
Q.5 A parallel beam of monochromatic light is incident on a
narrow rectangular slit of width 1mm. When the diffraction
pattern is seen on a screen placed at a distance of 2m. the
width of principal maxima is found to be 2.5 mm. The wave
length of light is-
(a) 6250 nm (b) 6200 nm
(c) 5890 nm (d) 6000 nm
Page 2


DIRECTIONS (Q.1-Q.22) : There are 22 multiple choice
questions. Each question has 4 choices (a), (b), (c) and (d), out
of which ONLY ONE choice is correct.
Q.1 The first diffraction minima due to a single slit diffraction
is at q = 30° for a light of wavelength 5000Å. The width of
the slit is-
(a) 5 × 10
–5
 cm (b) 1.0 × 10
–4
 cm
(c) 2.5 × 10
–5
 cm (d) 1.25 × 10
–5
 cm
Q.2 Two spectral line of sodium D
1
 & D
2
 have wavelengths of
approximately 5890Å and 5896Å. A sodium lamp sends
incident plane wave on to a slit of width 2 micrometre. A
screen is located  at 2m from the slit. Find the spacing
between the first maxima of two sodium lines as measured
on the screen.
(a) 10
–4
 m (b) 9 × 10
–4
 m
(c) 9 × 10
4
 m (d) None
Q.3 Width of slit is 0.3mm. Fraunhoffer diffraction is observed
in focus plane of lense of a lense of focal length 1 m. If
third minima is at 5 mm distance from central maxima,
then wavelength of light is-
(a) 7000Å (b) 6500Å (c) 6000Å (d) 5000Å
Q.4 When a wave of  wavelength 0.2 cm is made incident
normally on a slit of width 0.004m, then the semi-angular
width of central maximum of diffraction pattern will be-
(a) 60° (b) 30° (c) 90° (d) 0°
Q.5 A parallel beam of monochromatic light is incident on a
narrow rectangular slit of width 1mm. When the diffraction
pattern is seen on a screen placed at a distance of 2m. the
width of principal maxima is found to be 2.5 mm. The wave
length of light is-
(a) 6250 nm (b) 6200 nm
(c) 5890 nm (d) 6000 nm
2
DPP/ P 53
Q.6 Light of wavelength 6328Å is incident normally on slit
having a width of 0.2 mm. The width of the central
maximum measured  from minimum to minimum of
diffraction pattern on a screen 9.0 meters away will be
about -
(a) 0.36° (b) 0.18°
(c) 0.72° (d) 0.09°
Q.7 A screen is placed 2m away from the single narrow slit.
Calculate the slit width if the first minimum lies 5mm on
either side of the central maximum. Incident plane waves
have a wavelenght of 5000Å.
(a) 2 × 10
–4
 m (b) 2 × 10
–3
 cm
(c) 2 × 10
–4
 cm (d) None
Q.8 Red light of wavelength 6500Å from a distant source falls
on a slit 0.5 mm wide. What is the distance between two
dark bands on each side of central bright band of diffraction
pattern observed on a screen placed 1.8 m from the slit.
(a) 4.68 × 10
–3
 cm (b) 4.68 × 10
–3
 mm
(c) 4.68 × 10
–3
 nm (d) 4.68 × 10
–3
 m
Q.9 Fraunhoffer diffraction pattern is observed at a distance
of 2m on screen, when a plane-wavefront of 6000Å is
incident perpendicularly on 0.2 mm wide slit.Width of
central maxima is:
(a) 10 mm (b) 6 mm
(c) 12 mm (d) None of these
Q.10 A diffraction pattern is produced by a single slit of width
0.5mm with the help of a convex lens of focal length 40cm.
If the  wavelength of light used is 5896Å. then the distance
of first dark fringe from the axis will be-
(a) 0.047 cm (b) 0.047 m
(c) 0.047 mm (d) 47 cm
Q.11 What should be the size of the aperture of the objective of
telescope which can just resolve the two stars of angular
width of 10
–3
 degree by light of wavelength 5000Å?
(a) 3.5 cm (b) 3.5 mm
(c) 3.5 m (d) 3.5 km
Q.12 Image of sun formed due to reflection at air water interface
is found to be very highly polarised. Refractive index of
water being m = 4/3, find the angle of sun above the horizon.
(a) 36.9º (b) 26.9º
(c) 16.9º (d) 46.9º
Q.13 When light of a certain wavelength is incident on a plane
surface of a material at a glancing angle 30º, the reflected
light is found to be completely plane polarised. Determine
refractive index of given material –
(a)
3
(b)
2
(c) 1/2 (d)2
Q.14 Two polaroids are oriented with their planes perpendicular
to incident light and transmission axis making an angle of
30º with each other. What fraction of incident unpolarised
light is transmitted ?
(a) 57.5 % (b) 17.5 %
(c) 27.5 % (d) 37.5 %
Q.15Unpolarised light of intensity 32 Wm
–2
 passes through
three polarisers such that the transmission axis of the last
polariser is crossed with the first. If the intensity of the
emerging light is 3 Wm
–2
. At what angle will the
transmitted intensity be maximum ?
(a) 45º (b) 15º
(c) 35º (d) 75º
Q.16 V
0
 and V
E
 represent the velocities, m
0
 and  m
E
 the refractive
indices of ordinary and extraordinary rays for a doubly
refracting crystal. Then
(a)V
0
  ³ V
E
, m
0 
 £  m
E
 if the crystal is calcite
(b)V
0
  £ V
E
, m
0 
 £  m
E
 if the crystal is quartz
(c)V
0
  £ V
E
, m
0 
 ³  m
E
  if the crystal is calcite
(d)V
0
  ³ V
E
, m
0 
  ³  m
E
 if the crystal is quartz
Page 3


DIRECTIONS (Q.1-Q.22) : There are 22 multiple choice
questions. Each question has 4 choices (a), (b), (c) and (d), out
of which ONLY ONE choice is correct.
Q.1 The first diffraction minima due to a single slit diffraction
is at q = 30° for a light of wavelength 5000Å. The width of
the slit is-
(a) 5 × 10
–5
 cm (b) 1.0 × 10
–4
 cm
(c) 2.5 × 10
–5
 cm (d) 1.25 × 10
–5
 cm
Q.2 Two spectral line of sodium D
1
 & D
2
 have wavelengths of
approximately 5890Å and 5896Å. A sodium lamp sends
incident plane wave on to a slit of width 2 micrometre. A
screen is located  at 2m from the slit. Find the spacing
between the first maxima of two sodium lines as measured
on the screen.
(a) 10
–4
 m (b) 9 × 10
–4
 m
(c) 9 × 10
4
 m (d) None
Q.3 Width of slit is 0.3mm. Fraunhoffer diffraction is observed
in focus plane of lense of a lense of focal length 1 m. If
third minima is at 5 mm distance from central maxima,
then wavelength of light is-
(a) 7000Å (b) 6500Å (c) 6000Å (d) 5000Å
Q.4 When a wave of  wavelength 0.2 cm is made incident
normally on a slit of width 0.004m, then the semi-angular
width of central maximum of diffraction pattern will be-
(a) 60° (b) 30° (c) 90° (d) 0°
Q.5 A parallel beam of monochromatic light is incident on a
narrow rectangular slit of width 1mm. When the diffraction
pattern is seen on a screen placed at a distance of 2m. the
width of principal maxima is found to be 2.5 mm. The wave
length of light is-
(a) 6250 nm (b) 6200 nm
(c) 5890 nm (d) 6000 nm
2
DPP/ P 53
Q.6 Light of wavelength 6328Å is incident normally on slit
having a width of 0.2 mm. The width of the central
maximum measured  from minimum to minimum of
diffraction pattern on a screen 9.0 meters away will be
about -
(a) 0.36° (b) 0.18°
(c) 0.72° (d) 0.09°
Q.7 A screen is placed 2m away from the single narrow slit.
Calculate the slit width if the first minimum lies 5mm on
either side of the central maximum. Incident plane waves
have a wavelenght of 5000Å.
(a) 2 × 10
–4
 m (b) 2 × 10
–3
 cm
(c) 2 × 10
–4
 cm (d) None
Q.8 Red light of wavelength 6500Å from a distant source falls
on a slit 0.5 mm wide. What is the distance between two
dark bands on each side of central bright band of diffraction
pattern observed on a screen placed 1.8 m from the slit.
(a) 4.68 × 10
–3
 cm (b) 4.68 × 10
–3
 mm
(c) 4.68 × 10
–3
 nm (d) 4.68 × 10
–3
 m
Q.9 Fraunhoffer diffraction pattern is observed at a distance
of 2m on screen, when a plane-wavefront of 6000Å is
incident perpendicularly on 0.2 mm wide slit.Width of
central maxima is:
(a) 10 mm (b) 6 mm
(c) 12 mm (d) None of these
Q.10 A diffraction pattern is produced by a single slit of width
0.5mm with the help of a convex lens of focal length 40cm.
If the  wavelength of light used is 5896Å. then the distance
of first dark fringe from the axis will be-
(a) 0.047 cm (b) 0.047 m
(c) 0.047 mm (d) 47 cm
Q.11 What should be the size of the aperture of the objective of
telescope which can just resolve the two stars of angular
width of 10
–3
 degree by light of wavelength 5000Å?
(a) 3.5 cm (b) 3.5 mm
(c) 3.5 m (d) 3.5 km
Q.12 Image of sun formed due to reflection at air water interface
is found to be very highly polarised. Refractive index of
water being m = 4/3, find the angle of sun above the horizon.
(a) 36.9º (b) 26.9º
(c) 16.9º (d) 46.9º
Q.13 When light of a certain wavelength is incident on a plane
surface of a material at a glancing angle 30º, the reflected
light is found to be completely plane polarised. Determine
refractive index of given material –
(a)
3
(b)
2
(c) 1/2 (d)2
Q.14 Two polaroids are oriented with their planes perpendicular
to incident light and transmission axis making an angle of
30º with each other. What fraction of incident unpolarised
light is transmitted ?
(a) 57.5 % (b) 17.5 %
(c) 27.5 % (d) 37.5 %
Q.15Unpolarised light of intensity 32 Wm
–2
 passes through
three polarisers such that the transmission axis of the last
polariser is crossed with the first. If the intensity of the
emerging light is 3 Wm
–2
. At what angle will the
transmitted intensity be maximum ?
(a) 45º (b) 15º
(c) 35º (d) 75º
Q.16 V
0
 and V
E
 represent the velocities, m
0
 and  m
E
 the refractive
indices of ordinary and extraordinary rays for a doubly
refracting crystal. Then
(a)V
0
  ³ V
E
, m
0 
 £  m
E
 if the crystal is calcite
(b)V
0
  £ V
E
, m
0 
 £  m
E
 if the crystal is quartz
(c)V
0
  £ V
E
, m
0 
 ³  m
E
  if the crystal is calcite
(d)V
0
  ³ V
E
, m
0 
  ³  m
E
 if the crystal is quartz
DPP/ P
3
53
Q.17 A ray of light is incident on the surface of a glass plate at
an angle of incidence equal to Brewster’s angle f. If m
represents the refractive index of glass with respect to air.
then the angle between reflected and refracted rays is
(a) 90° + f (b) sin
–1 
(m cosf)
(c) 90° (d) 90° – sin
–1 
( cosf/m)
Q.18A light has amplitude A and angle between analyser and
polariser is 60°. Light transmitted by analyser has
amplitude
(a)
2 A
(b)
/2 A
(c)
3 /2 A
(d) A/2
Q.19 A slit of size 0.15 cm is placed at 2.1 m from a screen. On
illuminating it by a light of wavelength 5×10
–5
 cm, the width
of central maxima will be
(a) 70 mm (b) 0.14 mm (c) 1.4 mm (d) 0.14 cm
Q.20 What will be the angle of diffraction for the first minimum
due to Fraunhoffer diffraction with sources of light of wave
lenght 550 nm and slit width 0.55 mm ?
(a) 0.001 rad (b) 0.01 rad
(c) 1 rad (d) 0.1 rad
Q.21 In Fresnel diffraction, if the distance between the disc and
the screen is decreased, the intensity of central bright spot
will
(a) increase (b) decrease
(c) remain constant (d) none of these
22. When an unpolarized light of intensity 
0
I is incident on a
polarizing sheet, the intensity of the light which does not
get transmitted is
(a)
0
1
4
I (b) 0
1
2
I
(c)
0
I (d) zero
DIRECTIONS (Q.23-Q.25) : 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.23Plane polarised light is passed through a polaroid. On
viewing through the polaroid we find that when the polariod
is given one complete rotation about the direction of the
light, which of the following is not observed ?
(1) The intensity of light gradually decreases to zero and
remains at zero
(2) The intensity of light gradually increases to a
maximum and remains at maximum
(3) There is no change in intensity
(4) The intensity of light is twice maximum and twice
zero
Q.24 Out of the following statements which are correct ?
(1) Nicol’s prism works on the principle of double
refraction and total internal reflection
(2) Nicol’s prism can be used to produce and analyse
polarised light
(3) Calcite and Quartz are both doubly refracting crystals
(4) When unpolarised light passes through a Nicol’s
prism, the emergent light is elliptically polarised
Q.25 Which statements are incorrect for a  zone plate and a lens?
(1) Zone plate has one focus whereas lens has multiple
focii
(2) Both zone plate and lens have multi focii
(3) Zone plate has one focus whereas a lens has infinite
(4) Zone plate has multi focii whereas lens has one
Page 4


DIRECTIONS (Q.1-Q.22) : There are 22 multiple choice
questions. Each question has 4 choices (a), (b), (c) and (d), out
of which ONLY ONE choice is correct.
Q.1 The first diffraction minima due to a single slit diffraction
is at q = 30° for a light of wavelength 5000Å. The width of
the slit is-
(a) 5 × 10
–5
 cm (b) 1.0 × 10
–4
 cm
(c) 2.5 × 10
–5
 cm (d) 1.25 × 10
–5
 cm
Q.2 Two spectral line of sodium D
1
 & D
2
 have wavelengths of
approximately 5890Å and 5896Å. A sodium lamp sends
incident plane wave on to a slit of width 2 micrometre. A
screen is located  at 2m from the slit. Find the spacing
between the first maxima of two sodium lines as measured
on the screen.
(a) 10
–4
 m (b) 9 × 10
–4
 m
(c) 9 × 10
4
 m (d) None
Q.3 Width of slit is 0.3mm. Fraunhoffer diffraction is observed
in focus plane of lense of a lense of focal length 1 m. If
third minima is at 5 mm distance from central maxima,
then wavelength of light is-
(a) 7000Å (b) 6500Å (c) 6000Å (d) 5000Å
Q.4 When a wave of  wavelength 0.2 cm is made incident
normally on a slit of width 0.004m, then the semi-angular
width of central maximum of diffraction pattern will be-
(a) 60° (b) 30° (c) 90° (d) 0°
Q.5 A parallel beam of monochromatic light is incident on a
narrow rectangular slit of width 1mm. When the diffraction
pattern is seen on a screen placed at a distance of 2m. the
width of principal maxima is found to be 2.5 mm. The wave
length of light is-
(a) 6250 nm (b) 6200 nm
(c) 5890 nm (d) 6000 nm
2
DPP/ P 53
Q.6 Light of wavelength 6328Å is incident normally on slit
having a width of 0.2 mm. The width of the central
maximum measured  from minimum to minimum of
diffraction pattern on a screen 9.0 meters away will be
about -
(a) 0.36° (b) 0.18°
(c) 0.72° (d) 0.09°
Q.7 A screen is placed 2m away from the single narrow slit.
Calculate the slit width if the first minimum lies 5mm on
either side of the central maximum. Incident plane waves
have a wavelenght of 5000Å.
(a) 2 × 10
–4
 m (b) 2 × 10
–3
 cm
(c) 2 × 10
–4
 cm (d) None
Q.8 Red light of wavelength 6500Å from a distant source falls
on a slit 0.5 mm wide. What is the distance between two
dark bands on each side of central bright band of diffraction
pattern observed on a screen placed 1.8 m from the slit.
(a) 4.68 × 10
–3
 cm (b) 4.68 × 10
–3
 mm
(c) 4.68 × 10
–3
 nm (d) 4.68 × 10
–3
 m
Q.9 Fraunhoffer diffraction pattern is observed at a distance
of 2m on screen, when a plane-wavefront of 6000Å is
incident perpendicularly on 0.2 mm wide slit.Width of
central maxima is:
(a) 10 mm (b) 6 mm
(c) 12 mm (d) None of these
Q.10 A diffraction pattern is produced by a single slit of width
0.5mm with the help of a convex lens of focal length 40cm.
If the  wavelength of light used is 5896Å. then the distance
of first dark fringe from the axis will be-
(a) 0.047 cm (b) 0.047 m
(c) 0.047 mm (d) 47 cm
Q.11 What should be the size of the aperture of the objective of
telescope which can just resolve the two stars of angular
width of 10
–3
 degree by light of wavelength 5000Å?
(a) 3.5 cm (b) 3.5 mm
(c) 3.5 m (d) 3.5 km
Q.12 Image of sun formed due to reflection at air water interface
is found to be very highly polarised. Refractive index of
water being m = 4/3, find the angle of sun above the horizon.
(a) 36.9º (b) 26.9º
(c) 16.9º (d) 46.9º
Q.13 When light of a certain wavelength is incident on a plane
surface of a material at a glancing angle 30º, the reflected
light is found to be completely plane polarised. Determine
refractive index of given material –
(a)
3
(b)
2
(c) 1/2 (d)2
Q.14 Two polaroids are oriented with their planes perpendicular
to incident light and transmission axis making an angle of
30º with each other. What fraction of incident unpolarised
light is transmitted ?
(a) 57.5 % (b) 17.5 %
(c) 27.5 % (d) 37.5 %
Q.15Unpolarised light of intensity 32 Wm
–2
 passes through
three polarisers such that the transmission axis of the last
polariser is crossed with the first. If the intensity of the
emerging light is 3 Wm
–2
. At what angle will the
transmitted intensity be maximum ?
(a) 45º (b) 15º
(c) 35º (d) 75º
Q.16 V
0
 and V
E
 represent the velocities, m
0
 and  m
E
 the refractive
indices of ordinary and extraordinary rays for a doubly
refracting crystal. Then
(a)V
0
  ³ V
E
, m
0 
 £  m
E
 if the crystal is calcite
(b)V
0
  £ V
E
, m
0 
 £  m
E
 if the crystal is quartz
(c)V
0
  £ V
E
, m
0 
 ³  m
E
  if the crystal is calcite
(d)V
0
  ³ V
E
, m
0 
  ³  m
E
 if the crystal is quartz
DPP/ P
3
53
Q.17 A ray of light is incident on the surface of a glass plate at
an angle of incidence equal to Brewster’s angle f. If m
represents the refractive index of glass with respect to air.
then the angle between reflected and refracted rays is
(a) 90° + f (b) sin
–1 
(m cosf)
(c) 90° (d) 90° – sin
–1 
( cosf/m)
Q.18A light has amplitude A and angle between analyser and
polariser is 60°. Light transmitted by analyser has
amplitude
(a)
2 A
(b)
/2 A
(c)
3 /2 A
(d) A/2
Q.19 A slit of size 0.15 cm is placed at 2.1 m from a screen. On
illuminating it by a light of wavelength 5×10
–5
 cm, the width
of central maxima will be
(a) 70 mm (b) 0.14 mm (c) 1.4 mm (d) 0.14 cm
Q.20 What will be the angle of diffraction for the first minimum
due to Fraunhoffer diffraction with sources of light of wave
lenght 550 nm and slit width 0.55 mm ?
(a) 0.001 rad (b) 0.01 rad
(c) 1 rad (d) 0.1 rad
Q.21 In Fresnel diffraction, if the distance between the disc and
the screen is decreased, the intensity of central bright spot
will
(a) increase (b) decrease
(c) remain constant (d) none of these
22. When an unpolarized light of intensity 
0
I is incident on a
polarizing sheet, the intensity of the light which does not
get transmitted is
(a)
0
1
4
I (b) 0
1
2
I
(c)
0
I (d) zero
DIRECTIONS (Q.23-Q.25) : 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.23Plane polarised light is passed through a polaroid. On
viewing through the polaroid we find that when the polariod
is given one complete rotation about the direction of the
light, which of the following is not observed ?
(1) The intensity of light gradually decreases to zero and
remains at zero
(2) The intensity of light gradually increases to a
maximum and remains at maximum
(3) There is no change in intensity
(4) The intensity of light is twice maximum and twice
zero
Q.24 Out of the following statements which are correct ?
(1) Nicol’s prism works on the principle of double
refraction and total internal reflection
(2) Nicol’s prism can be used to produce and analyse
polarised light
(3) Calcite and Quartz are both doubly refracting crystals
(4) When unpolarised light passes through a Nicol’s
prism, the emergent light is elliptically polarised
Q.25 Which statements are incorrect for a  zone plate and a lens?
(1) Zone plate has one focus whereas lens has multiple
focii
(2) Both zone plate and lens have multi focii
(3) Zone plate has one focus whereas a lens has infinite
(4) Zone plate has multi focii whereas lens has one
4
DPP/ P 53
DIRECTIONS (Q.26-Q.27) : Read the passage given below
and answer the questions that follows :
Angular width of central maximum in the Fraunhoffer-diffraction
pattern of a slit is measured. The slit is illuminated by light of
wavelength 6000 Å. When the slit is illuminated by light of
another wavelength, the angular width decreases by 30%.
Q.26 The wavelength of the light is
(a) 4200Å (b) 3500Å (c) 5000 Å (d) 5200Å
Q.27 The same decrease in the angular width of central maximum
is obtained when the original apparatus is immersed in a
liquid. Find refractive index of the liquid.
(a) 1.23 (b) 1.43 (c) 2.2 (d) 2.43
DIRECTIONS (Q. 28-Q.30) : 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.28 Statement-1 : The unpolarised light and polarised light
can be distinguished from each other by using polaroid.
Statement-2 : A polaroid is capable of producing plane
polarised beams of light.
Q.29 Statement-1 : Nicol prism is used to produce and analyse
plane polarised light.
Statement-2 : Nicol prism reduces the intensity of light
to zero.
Q.30 Statement-1 : The cloud in sky generally appear to be
whitish.
Statement-2 : Diffraction due to clouds is efficient in equal
measure at all wavelengths.