IISER Physics - Wave Optics
Exam Duration: 45 Mins Total Questions : 30
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
In a certain double slit experimental arrangement,interference fringes of width 1.0mm each are observed when light of wavelength 5000\(\mathring { A } \) is observed.If the light source is replaced by wavelength 6000\(\mathring { A } \), the fringe width will be
- (a)
0.5mm
- (b)
1.0mm
- (c)
1.2mm
- (d)
1.5mm
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 \({ y }_{ 1 }={ A }_{ 1 }\sin { (\omega t-{ \beta }_{ 1 }) } \)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)
\(\left| { A }_{ 1 }+{ A }_{ 2 } \right| \)
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
In young's experiment, if the slit separation is amde 3 folds, the fringes width becomes
- (a)
1/3 fold
- (b)
3 fold
- (c)
9 fold
- (d)
same
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
In a double slit arrangement mono-chromatic light gives fringes on a screen.If the screen is moved by \(5\times { 10 }^{ -2 }\)m towards the slits,the change in fringe width is \(3\times { 10 }^{ -5 }\)m.If the distance between the slits is \({ 10 }^{ -3 }\)m, what is the wavelength of light used?
- (a)
5890\(\mathring { A } \)
- (b)
\(5000\mathring { A } \)
- (c)
\(6000\mathring { A } \)
- (d)
None of these
The beams of light having intensities I and 4I interface to produce a fringe pattern on a screen.The phase difference between the beams is \(\pi /2\)at point A and \(\pi\)at point B.then,the difference between the resultant intensities at A and B is
- (a)
2I
- (b)
4I
- (c)
5I
- (d)
7I
In young's double slit experiment, the intensity on screen at a point where path difference is \(\lambda\), is k. what will be intensity at the point where path difference is \(\lambda\)/4?
- (a)
K/4
- (b)
K/2
- (c)
K
- (d)
zero
In a biprism experiment, by using light of wavelength 5000\(\mathring { A } \), 5 mm wide fringes are obtained on a screen 1.0 m away from coherent sources.The separation between two coherent sources is
- (a)
1.0 mm
- (b)
0.1 mm
- (c)
0.05 mm
- (d)
0.01 mm
Four independent waves are expressed as
(i) \({ y }_{ 1 }={ a }_{ 1 }\quad \sin { \omega t } \)
(ii) \({ y }_{ 2 }={ a }_{ 2 }\quad \sin { (\omega t-kx) } \)
(iii) \({ y }_{ 3 }={ a }_{ 3 }\quad \sin { \quad 2\quad \omega t } \)
(iv) \({ y }_{ 4 }={ a }_{ 4 }\quad \sin { (\omega t+\frac { \pi }{ 3 } } )\)
The interference is possible between
- (a)
(i) and (ii)
- (b)
(i) and (iii)
- (c)
(i) and (iv)
- (d)
Not possible at all
To observe diffraction, the size of an aperture
- (a)
should be of the same order as wavelength of light used
- (b)
should be much larger than the wavelength
- (c)
have no relation to wavelength
- (d)
should be exactly \(\lambda/2\)
Penetration of light into the region of geometrically shadow is called
- (a)
Polarisation
- (b)
interference
- (c)
diffraction
- (d)
refraction
A diffraction pattern is obtained using a beam of red light.What will happen if red light is replaced by blue light?
- (a)
No change
- (b)
diffraction brands become narrower and crowded together
- (c)
bands become broader and farther apart
- (d)
bands disappear
The polariser is used to
- (a)
reduce intensity of light
- (b)
produce polarised light
- (c)
increase intensity of light
- (d)
produce unpolarised light
The given light of unknown state of polarisation is passed through a nicol prism.On rotating the nicol prism through \({ 360 }^{ \circ }\), rwo positions of maxima and two positions of extinctions of light are absorved.Then the state of polarisation of the given light must be
- (a)
linear
- (b)
elliptical
- (c)
circular
- (d)
random
A beam of light of wavelength 600nm from a distane source falls on a single slit.1.00mm wide and the resulting diffraction pattern is observed on a screen 2m away.The distance between the first dark fringes on either side of the central fringe is
- (a)
1.2 mm
- (b)
1.2 cm
- (c)
2.4 mm
- (d)
2.4 cm
Which of the following does not change when a wave travels from one medium to another medium?
- (a)
wavelength
- (b)
frequency
- (c)
velocity
- (d)
amplitude
In the ideal double-slit experiment, when a glass-plate of thickness't' is introduced in the path of one of the interfering beams, the intensity at the position where the central maximum occured previously remains unchanged. the minimum thickness of the glass-plate is
- (a)
\(2 \lambda\)
- (b)
\(2 \lambda/3\)
- (c)
\( \lambda/3\)
- (d)
\( \lambda\)
In a young's double slit experiment using monochromatic light the fringe pattern shifts by a certain distance \({ x } _ { 0 } \) on the screen when a mica sheet of refractive index \(\mu\) and thickness t is introduced in the path of one of the interfering waves. the mica sheet is then removed and the distance between the slits and the screen is doubled.It is found that the distance between successive maxima(or minima) now is the same as the observed fringe shift upon the introduction of the mica sheet.The wavelength of the monochromatic light used in the experiment is
- (a)
\(\lambda =(\mu -1)t\)
- (b)
\(\lambda =2(\mu -1)t\)
- (c)
\(\lambda =1/2\mu t\)
- (d)
\(\lambda =1/2(\mu -1)t\)
Consider sunlight incident on a slit of width \({ 10 }^{ 4 }\dot { A } \). The image seen through the slit shall
- (a)
be a fine sharp slit white in colour at the centre
- (b)
a bright slit white at the centre diffusing to zero intensity at the edges
- (c)
a bright slit white at the centre diffusing to regions of different colours
- (d)
only be a diffused slit white in colour
In the ideal double slit experiment, when a glass-plate (refractive index 1.5) of thickness t is introduced in the path of one interfering beams (wavelength \(\lambda \)), the intensity at the position where the central maximum occured previously remain unchanged. The minimum thickness of the glass plate is
- (a)
\(2\lambda \)
- (b)
\(\frac { 2\lambda }{ 3 } \)
- (c)
\(\frac { \lambda }{ 3 }\)
- (d)
\( { \lambda }\)
Two non-coherent sources emit light beams of intensities I and 4I. The maximum and minimum intensities in the resulting beam are
- (a)
9I and I
- (b)
9I and 3I
- (c)
5I and I
- (d)
5I and 3I
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 %
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
In a Young's double slit experiment, the intensity at a point where the path difference is \(\frac { \lambda }{ 6 } \) (\(\lambda \) being the wavelength of the light used) is I. If I0 denotes the maximum intensity, then I/I0 is equal to
- (a)
\(\frac { 1 }{ \sqrt { 2 } } \)
- (b)
\(\frac { \sqrt { 3 } }{ 2 } \)
- (c)
\(\frac{1}{2}\)
- (d)
\(\frac{3}{4}\)
The angle of incidence at which reflected light is totally polarised for reflection from air to glass (refractive index n), is
- (a)
\(\sin ^{ -1 }{ n } \)
- (b)
\(\sin ^{ -1 }{ 1/n } \)
- (c)
\(\tan ^{ -1 }{ 1/n } \)
- (d)
\(\tan ^{ -1 }{ n } \)
The maximum number of possible interference maxima for slit-separation equal to twice the wavelength in Young's double slit experiment, is
- (a)
infinite
- (b)
five
- (c)
three
- (d)
zero