Physics - Wave Optics
Exam Duration: 45 Mins Total Questions : 30
When light wave suffers reflection at the interface from air to glass,the change in phase of the reflected light is equal to
- (a)
0
- (b)
\({\pi} / { 2 }\)
- (c)
\(\pi\)
- (d)
\(2{\pi }\)
Ray optics is valid, when characteristic dimensions are
- (a)
much smaller than the wavelength of light
- (b)
much larger than the wavelength of light
- (c)
of the same order as the wavelength of light
- (d)
of the order of one millimetre
For the sustained interference of light,the necessary conditiion is that the two sources should
- (a)
have constant phase difference
- (b)
have the same state of polarisation
- (c)
be close to each other
- (d)
have large distance apart from the screen
In young's double slit experiment, ratio of intensities of a bright band and a dark band is 16:1. the ratio of amplitudes of interfering waves is
- (a)
16
- (b)
5/3
- (c)
4
- (d)
1/4
Two waves having intensity in the ratio 25:4 produce interference.The ratio of the maximum to minimum intensity is:
- (a)
5:2
- (b)
7:3
- (c)
49:9
- (d)
9:49
Two waves \({ y }_{ 1 }={ A }_{ 1 }\sin { (\omega t-{ \beta }_{ 1 }) } \)and\({ y }_{ 2 }={ A }_{ 2 }\sin { (\omega t-{ \beta }_{ 2 }) } \)superimpose to form a resultant wave whose amplitude is
- (a)
\(\sqrt { { A }_{ 1 }^{ 2 }+{ A }_{ 2 }^{ 2 }+2{ A }_{ 1 }{ A }_{ 2 }\cos { ({ \beta }_{ 1 }-{ \beta }_{ 2 }) } } \)
- (b)
\(\sqrt { { A }_{ 1 }^{ 2 }+{ A }_{ 2 }^{ 2 }+2{ A }_{ 1 }{ A }_{ 2 }\sin { ({ \beta }_{ 1 }-{ \beta }_{ 2 }) } } \)
- (c)
\({ A }_{ 1 }+{ A }_{ 2 }\)
- (d)
\(\left| { A }_{ 1 }+{ A }_{ 2 } \right| \)
A thin mica sheet of thickness \(2\times { 10 }^{ -6 }\)m and refractive index(\(\mu\)=1.5) is introduced in the path of one of the waves.The wavelength of the wave used is 5000 \(\mathring { A } \).The central bright maximum will shift
- (a)
2 fringes
- (b)
0.2 fringes
- (c)
10 fringes
- (d)
None of these
Interference pattern is obtained on a screen due to two identical coherent sources of monochromatic light.The intensity of central bright fringe is I.when one of the sources is blocked,its intensity becomes \({ I } _ { 0 }\).the intensity in two situations is related as
- (a)
I=\({ I } _ { 0 }\)
- (b)
I=\(2{ I } _ { 0 }\)
- (c)
I=\(3{ I } _ { 0 }\)
- (d)
I=\(4{ I } _ { 0 }\)
What happens to the pattern in young's experiment when the monochromatic source is replaced by the white-light source?
- (a)
All bright fringes become white
- (b)
No fringes are observed
- (c)
All bright fringes get coloured from violet to red
- (d)
Only the central fringe is achromatic, all other fringes are coloured
Two coherent sources send beams of intensity I and 4I.the maximum and minimum possible intensities in the resulting beam are
- (a)
5I and I
- (b)
5I and 3I
- (c)
9I and I
- (d)
9I and 3I
The contrast in the fringes in the interference pattern depends upon
- (a)
fringe width
- (b)
intensity ratio of the sources
- (c)
distance between the slits
- (d)
wavelengths
In an arrangement of double slit, the slits are illuminated by the light wavelength 600nm.Find the distance of the first point on the screen from the central maximum where intensity is 75% of the central maximum.The screen is 1 m away and slits are 2.1 mm apart
- (a)
\(4.8\times { 10 }^{ -6 }\)m
- (b)
\(4.8\times { 10 }^{ -3 }\)m
- (c)
\(4.8\times { 10 }^{ -5 }\)m
- (d)
None of the above
oil floating on water looks coloured due to interference of light.The approximate thickness of oil for such effect to be visible is
- (a)
100 \(\mathring { A } \)
- (b)
10,000 \(\mathring { A } \)
- (c)
1 mm
- (d)
1 cm
A thin air film between a plane glass plate and a convex lens is irradiated with parallel beam of monochromatic light and is observed under microscope. It will produce
- (a)
Uniform brightness
- (b)
complete darkness
- (c)
field crossed over by concentric bright and dark fringes
- (d)
field crossed over by parallel bright and dark fringes
In young's double slit experiment, two slits act as coherent sources of equal amplitude A and of wavelength \(\lambda\).In another experiment with the same set up, the two slits are sources of again of same amplitude A and wavelength \(\lambda\) but are incoherent.The ratio of intensity at the mid-point of the screen in the first case to that in the second case i.e,(\({ I }_ { 1 }/{ I } { 2 }\)) is
- (a)
1:2
- (b)
2:1
- (c)
1:4
- (d)
4:1
A parallel beam of light of wavelength 5000\(\mathring { A } \) is incident normally on a single slit of width 0.001 mm.The light is focused by a convex lens on a screen placed in focal plane. the first minimum is formed for the angle of diffraction equal to
- (a)
\({ 0 }^{ \circ }\)
- (b)
\({ 15 }^{ \circ }\)
- (c)
\({ 30 }^{ \circ }\)
- (d)
\({ 60 }^{ \circ }\)
Penetration of light into the region of geometrically shadow is called
- (a)
Polarisation
- (b)
interference
- (c)
diffraction
- (d)
refraction
Light is incident normally on a diffraction grating through which the first order diffraction is seen at \({ 32 }^{ \circ }\). the second order diffraction will be seen at
- (a)
\({ 48 }^{ \circ }\)
- (b)
\({ 64 }^{ \circ }\)
- (c)
\({ 80 }^{ \circ }\)
- (d)
There is no second order diffraction in this case
A rocket is going away from the earth at a speed 0.2 c, where c=speed of light.It emits signals of frequency \(4\times { 10 }^{ 7 }Hz\).What will be frequency observed by an observer on the earth?
- (a)
\(4\times { 10 }^{ 6 }Hz\)
- (b)
\(3.2\times { 10 }^{ 7 }Hz\)
- (c)
\(3\times { 10 }^{ 6 }Hz\)
- (d)
\(5\times { 10 }^{ 7 }Hz\)
A radio wave of frequency 840 MHz is sent towards an aeroplane.The radio echo heard has a frequency 2.8kHz more than original frequency.The velocity of the aeroplane is
- (a)
\(3{ kms }^{ -1 }\)
- (b)
\(2 { kms }^{ -1 }\)
- (c)
\(4 { kms }^{ -1 }\)
- (d)
\(0.5 { kms }^{ -1 }\)
In Young's experiment, the wavelength of red light is 7.8 x 10-5 cm and that of blue light is 5.2 x 10-5 cm. The value of n for which (n + 1)th blue light band coincides with nth red band is
- (a)
4
- (b)
2
- (c)
3
- (d)
1
A beam of ordinary unpolarised light passes through a tourmaline crystal C1 and then it passes through another tourmaline crystal C2 , which is oriented such that its principal plane is parallel to that of C2. The intensity of emergent light is I0. Now, C2 is rotated by 60° about the ray. The emergent ray will have intensity
- (a)
\(2{ I }_{ 0 }\)
- (b)
\({ I }_{ 0 }/\sqrt { 2 } \)
- (c)
\({ I }_{ 0 }/{ 4 } \)
- (d)
\({ I }_{ 0 }/\sqrt { 2 } \)
Two polaroids are kept crossed to each other. Now one of them is rotated through an angle of 45°. The percentage of incident light now transmitted through the system is
- (a)
15 %
- (b)
25 %
- (c)
50 %
- (d)
60 %
Match the laws given in column I with their formula given in column II and select the correct option from the choices given.
Column I | Column II |
A. Laws of refraction | 1. \(\mu =\tan { { i }_{ p } } \) |
B. Malus law | 2.\(\frac { \sin { i } }{ \sin { r } } \) = constant |
C. Brewster's law | 3.\(I\infty \cos ^{ 2 }{ \theta } \) |
- (a)
A B C 2 3 1 - (b)
A B C 1 2 3 - (c)
A B C 3 2 1 - (d)
A B C 2 1 3
In Young's double slit experiment, one of the slit is wider than other, so that amplitude of the light from one slit is double of that from other slit. If Im be the maximum intensity, the resultant intensity I, when they interfere at phase difference \(\phi \), is given by
- (a)
\(\frac { { I }_{ m } }{ 9 } \left( 4+5\cos { \phi } \right) \)
- (b)
\(\frac { { I }_{ m } }{ 3 } \left( 1+2\cos ^{ 2 }{ \frac { \phi }{ 2 } } \right) \)
- (c)
\(\frac { { I }_{ m } }{ 5 } \left( 1+4\cos ^{ 2 }{ \frac { \phi }{ 2 } } \right) \)
- (d)
\(\frac { { I }_{ m } }{ 9 } \left( 1+8\cos ^{ 2 }{ \frac { \phi }{ 2 } } \right) \)
At two points P and Q on screen in Young's double slit experiment, waves from slits S1 and S2 have a path difference of 0 and \(\lambda /4\) respectively.The ratio of intensities at P and Q will be
- (a)
3 : 2
- (b)
2 : 1
- (c)
\(\sqrt{2} : 1\)
- (d)
4 : 1
When an unpolarised light of intensity I0 is incident on a polarising sheet, the intensity of the light which does not get transmitted is
- (a)
\(\frac { 1 }{ 2 } { I }_{ 0 }\)
- (b)
\(\frac { 1 }{ 4 } { I }_{ 0 }\)
- (c)
zero
- (d)
\( { I }_{ 0 }\)