Polarisation

Q.

Light with an average flux of $20\raisebox{1ex}{$W$}\!\left/ \!\raisebox{-1ex}{$c{m}^2$}\right.$ falls on a non-reflecting surface at normal incidence having surface area $20c{m}^2$. The energy received by the surface during the time span of $1minute$ is

Q. Capacity of an isolated sphere is increased $n$ times when it is enclosed by an earthed concentric sphere. the ratio of their radii is

1. $\frac{n^2}{n-1}$
   
2. $\frac{n}{n-1}$
   
3. $\frac{2n}{n+1}$
   
4. $\frac{2n+1}{n+1}$
   

Q.

Find the maximum angle of refraction when a light ray is refracted from glass $(\mu =1.50)$ to air.

Q.

A source S and a detector D are placed at a distance d apart. A big cardboard is placed at a distance $\sqrt{2}d$ from the source and the detector as shown in figure (16-E2). The source emits a wave of wavelength = $\frac{d}{2}$ which is received by the detector after reflection from the cardboard. It is found to be in phase with the direct wave received from the source. By what minimum distance should the cardboard be shifted away so that the reflected wive becomes out of phase with the direct wave ?

Q.

The phenomenon of polarization shows that light has ________ nature.

1. Particle

2. Transverse

3. Longitudinal

4. Dual

Q. An unpolarised beam of light is made to incident on an arrangement of four polarsing sheets arranged in such a way that the characteristic direction of each polarizing sheet makes an angle of ${45}^{\circ }$ with that of preceding sheet. What fraction of incident unpolarised light will be transmitted finally?

1. $\frac{1}{2}$
2. $\frac{1}{8}$
3. $\frac{1}{16}$
4. $\frac{1}{4}$

Q. For a prism, its refractive index is $\cot \frac{A}{2}$. Then the minimum angle of deviation is-

1. ${180}^{\circ }-A$
2. ${180}^{\circ }-2A$
3. ${90}^{\circ }-A$
4. $\frac{A}{2}$

Q. The angle of deviation $\left(\delta \right)$ vs angle of incidence $\left(i\right)$ is plotted for a prism. Pick up the incorrect statement

1. The angle of prism is ${60}^{\circ }$.
2. The refractive index of the prism is $\mu =\sqrt{3}$.
3. For deviation to be ${65}^{\circ }$ the angle of incidence $i_1={55}^{\circ }$.
4. The curve of $\delta$ vs $i$ is parabolic.

Q. A linearly polarized electromagnetic wave in vacuum, is $E=3.1\cos \left[\right(1.8)z-(5.4\times {10}^6\left)t\right]\hat{i}\text{N/C}$. It is incident normally on a perfectly reflecting wall, at $z=a$. Choose the correct option.

1. The transmitted wae will be $3.1cos\left[\right(1.8)z-(5.4\times {10}^6\left)t\right]\hat{i}\frac{N}{C}$
2. The frequency of electromagnetic wave is $54\times {10}^4\text{Hz}$
3. The reflected wave will be $3.1\cos \left[\right(1.8)z+(5.4\times {10}^6\left)t\right]\hat{i}\text{N/C}$
4. The wavelength is $5.4\text{m}$

Q. A dip needle vibrates in the vertical plane perpendicular to the magnetic meridian. The time period of vibration is found to be 2 seconds. The same needle is then allowed to vibrate in the horizontal plane and the time period is again found to be 2 seconds. Then the angle of dip is

1. $0^{\circ }$
2. ${90}^{\circ }$
3. ${30}^{\circ }$
4. ${45}^{\circ }$

Q. In the propagation of electromagnetic waves, the angle between the direction of propagation and plane of polarization is

1. $Zero$
2. ${90}^{\circ }$
3. ${180}^{\circ }$
4. ${45}^{\circ }$

Q.

(a) In young’s double slit experiment, deduce the conditions for obtaining constructive and destructive interference fringes. Hence, deduce the expression for the fringe width.

(b)Show that the fringe pattern on the screen is actually a superposition of slit diffraction from each slit.

(c) What should be the width of each slit to obtain 10 maxima of the double slit pattern within the central maximum of the single slit pattern, for green light of wavelength 500 nm, if the separation between two slits is 1 mm?

OR

(a) Two thin convex lenses $L_1$and $L_2$ of focal lengths $f_1$and$f_2$ respectively, are placed coaxially in contact. An object is placed at a point beyond the focus of lens $L_1$ . Draw a ray diagram to show the image formation by the combination and hence derive the expression for the focal length of the combined system.

(b) A ray PQ incident on the face AB of a prism ABC, as shown in the figure, emerges from the face AC such that AQ = AR

Draw the ray diagram showing the passage of the ray through the prism. If the angle of the prism is ${60}^0$ and refractive index of the material of prism is $\sqrt{3}$. Determine the angle of incidence and angle of deviation

Q.

Which of the following shows the particle nature of light?

1. Refraction

2. Interference

3. Polarization

4. Photoelectric effect

Q. Identify the electromagnetic waves whose wavelengths vary as
(a) ${10}^{-12}m<\lambda <{10}^{-8}m$
(b) ${10}^{-3}m<\lambda <{10}^{-1}m$
Write one use for each.

Q. 16.The length of a vertical stick at the surface of a lake appears 12 cm to a fish under water. if refractive index of water is 4/3 , then actual length of stick above water surface is

Q.

The equation of Mohr's circle is given by $(\sigma -4{)}^2+{\tau }^2=9$where $\sigma$ is the normal stress and $\tau$ is the shear stress. The maximum shear stress is units. ,

1. 3

Q. Figure shows two coherent microwave source $S_1$ and $S_2$ emitting waves of wavelength $\lambda$ and separated by a distance $3\lambda$. For $\lambda <<D$ and $y\ne 0$, the minimum value of $y$ for point $P$ to be an intensity maximum is $\frac{D\sqrt{m}}{n}$ Determine the value of $m+n,$ if $m$ and $n$ are coprime numbers.

Q. Two infinitely long linear conductors are arranged perpendicular to each other and are in mutually perpendicular planes as shown in the figure. If $I_1=2$ $A$ along $y–axis$ and $I_2=3$ $A$ along $-vez–\text{axis}$ and $AP=AB=1cm$, the value of magnetic field strength $\overrightarrow{B}$ at $P$ is

1. $(-3\times {10}^{-5}T)\hat{j}+(4\times {10}^{-5}T)\hat{k}$
2. $(3\times {10}^{-5}T)\hat{j}+(4\times {10}^{-5}T)\hat{k}$
3. $(4\times {10}^{-5}T)\hat{j}+(3\times {10}^{-5}T)\hat{k}$
4. $(3\times {10}^{-5}T)\hat{j}+(-4\times {10}^{-5}T)\hat{k}$

Q. According to Brewster's law, except for polished metallic surfaces, the polarizing angle,

1. depends on wavelength and is different for different colours.
2. independent of wavelength and is different for different colours.
3. independent of wavelength and is same for different colours.
4. depends on wavelength and is same for differents colours.

Q. Through which of these can we distinguish the light waves from sound waves?

[CBSE PMT 1990; RPET 2000, 02]

1. Interference

2. Refraction

3. Polarisation

4. Reflection

Q. The polarizing angle for a piece of glass for green light is ${54.74}^{\circ }$. The angle of minimum deviation for an equilateral prism made of same glass is,
(Given : $\tan (54.74{)}^{\circ }=1.414$)

1. ${45}^{\circ }$
2. ${54.74}^{\circ }$
3. ${60}^{\circ }$
4. ${30}^{\circ }$

Q. If light shows properties like reflection , refraction, interference etc. and light is an electromagnetic wave than did other e.m. waves like Infrared or microwave etc. show these properties ?

Q. The given figure shows infinitely long bent wires in the $x-y$ plane of paper and each carrying a current $i$. Here $O$ is the origin. Co-ordinates of points $P$ and $Q$ are $(2m,0)$ and $(6m,0)$, respectively. Magnetic induction at $P$ is given by $\frac{\alpha {\mu }_{0}i}{32\pi }$. Find the value of $\alpha$.

Q.

Which of the following statements indicates that light waves are transverse?

1. Light waves can travel in vacuum.

2. Light waves show interference.

3. Light waves can be polarized.

4. Light waves can be diffracted.

Q. Two circular coils $X$ and $Y$, having equal number of turns, carry equal currents in the same sense and subtend same solid angle at point $O$. If the smaller coil, $X$ is midway between $O$ and $Y$, then if we represent the magnetic induction due to bigger coil $Y$ at $O$ as $B_Y$ and that due to smaller coil $X$ at $O$ as $B_X$ then

1. $\frac{B_Y}{B_X}=1$
2. $\frac{B_Y}{B_X}=\frac{1}{2}$
3. $\frac{B_Y}{B_X}=\frac{1}{4}$
4. $\frac{B_Y}{B_X}=2$

Q. A thin slice is cut out of a glass cylinder along a plane parallel to its axis. The slice is placed on a flat glass platewith the curved surface downwards. Monochromatic light is incident normally from the top. The observedinterference fringes from the combination do not follow on of the following statements.(A) The fringes are straight and parallel to the length of the piece.(B) The line of contact of the cylindrical glass piece and the glass plate appears dark.(C) The fringe spacing increases as we gooutwards.(D) The fringes are formed due to the interference of light rays reflected from the curved surface of the Cylindrical piece and the top surface of the glass plate.

Q. When unpolarised light passes through a Polaroid sheet the beam that emerges from it is plane polarized. This is due to selective :

1. absorption of the E-Ray
2. absorption of the O-Ray
3. absorption of the E & O Rays
4. reflection of one of the rays

Q. Light of intensity $=3{\text{W/m}}^2$ is incident on a perfectly absorbing metal surface of area $1{\text{m}}^2$ making an angle of ${60}^{\circ }$ with the normal. If the force exerted by the photons on the surfae is $p\times {10}^{-9}$ (in newton) find the value of $p$.

Q. A rod $AB$ of length $L$ is hung from two identical wires $1$ and $2$. A block of mass $m$ is hung at point $O$ of the rod as shown in Fig. The value of $x$ so that a tuning fork excites the fundamental mode in wire $1$ and the second harmonic in wire $2$ is

1. $\frac{L}{5}$
2. $\frac{L}{4}$
3. $\frac{L}{3}$
4. $\frac{2L}{3}$

Q. A travelling telescope is focussed at bottom of a †an k over a coin.Now †an k is filled upto height of 25 cm with a liquid of refractive index 1.6 by what dis†an ce would telescope be moved to focus on the coin again?