Intensity of Polarised Light

Q.

What is the dispersive power of the prism and its SI unit?

Q. $A$ system of three polarizers $P_1,P_2,P_3$ is set up such that the pass axis of $P_3$ is crossed with respect to that of $P_1$. The pass axis of $P_2$ is inclined at ${60}^{\circ }$ to the pass axis of $P_3$. When a beam of unpolarized light of intensity $I_0$ is incident on $P_1$ the intensity of light transmitted by three polarizers is $I$. The ratio $\left(\frac{I_0}{I}\right)$ equals (nearly)

1. $\frac{16}{3}$
2. $\frac{3}{32}$
3. $\frac{32}{3}$
4. $\frac{3}{16}$

Q. An unpolarized light of intensity $I_0$ passes through three successive Polaroids $P_1,P_2$ and $P_3$. The polarization axes of $P_1$ make an angle ${60}^{\circ }$ with $P_2$ and $P_2$ makes an angle ${30}^{\circ }$ with $P_3$. The intensity of the transmitted light from $P_3$ is

1. $\frac{3I_0}{32}$
2. $\frac{5I_0}{32}$
3. $\frac{I_0}{32}$
4. $\frac{3I_0}{16}$

Q.

When unpolarized light is passed through a polarizer its intensity

1. There is no effect on the unpolarized light.

2. The intensity of the unpolarized light increases.

3. The intensity of the unpolarized light decreases.

4. The intensity of the unpolarized light becomes zero.

Q. Two Nicol prisms are oriented with their principal planes making an angle of ${60}^{\circ }$. The percentage of incident unpolarized light which passes through the system is,

1. $50\%$
2. $100\%$
3. $12.5\%$
4. $25\%$

Q. Two polaroids are present in the path of unpolarized beam of intensity $I_0$ such that no light is emitted from the second polaroid. If a third polaroid, whose transmission axis makes an angle $\theta$ with the transmission axis of the first polaroid, is placed between these polaroids. Then the intensity of light emerging from the last polaroid will be,

1. $\left(\frac{I_0}{8}\right){\sin }^{2}2\theta$
2. $\left(\frac{I_0}{4}\right){\sin }^{2}2\theta$
3. $\left(\frac{I_0}{4}\right){\cos }^4\theta$
4. $\left(\frac{I_0}{2}\right){\cos }^4\theta$

Q. The physical sizes of the transmitter and receiver antenna in a communication system are-

1. Proportional to carrier frequency
2. Inversely proportional to carrier frequency
3. Independent of both carrier and modulation frequency
4. Inversely proportional to modulation frequency

Q. In a stack of three polarizing sheets the first and third are crossed while the middle one has its axis at ${45}^{\circ }$ to the axes of the other two. The fraction of the intensity of an incident unpolarized beam of light that is transmitted by the stack is

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

Q. Unpolarized light with an intensity of $I_0=16\frac{W}{m^2}$ is incident on a pair of polarizers. The first polarizer has its transmission axis aligned at ${50}^{\circ }$ from the vertical. The second polarizer has its transmission axis aligned at ${20}^{\circ }$ from the vertical.

What is the intensity of the light when it emerges from the second polarizer?

1. $4\frac{W}{m^2}$
2. $8{\cos }^2{20}^{\circ }\frac{W}{m^2}$
3. $6\frac{W}{m^2}$
4. $12\frac{W}{m^2}$

Q. A beam of plane polarized light falls normally on a polarizer of cross sectional area $3\times {10}^{–4}{\text{m}}^2$. Flux of energy of incident ray is ${10}^{–3}$ Watt. The polarizer rotates with an angular frequency of $31.4{\text{rad s}}^{–1}$. The energy of light passing through the polarizer per revolution will be -

1. ${10}^{-4}\text{Joule}$
2. ${10}^{-3}\text{Joule}$
3. ${10}^{-2}\text{Joule}$
4. ${10}^{-1}\text{Joule}$

Q. An unpolarised beam of intensity $I_0$ is incident on a pair of Nicol prisms making an angle of ${60}^{\circ }$ with each other. The intensity of light emerging from the pair is-

1. $I_0$
2. $\frac{I_0}{2}$
3. $\frac{I_0}{4}$
4. $\frac{I_0}{8}$

Q.

The minimum deviations suffered by red, yellow and violet beams passing through an equilateral transparent prism are ${38.4}^{\circ },{38.7}^{\circ }$ and ${39.2}^{\circ }$ respectively. Calculate the dispersive power of the medium.

Q.

An unpolarised beam of intensity 2a² passes through a thin polaroid. Assuming zero absorption in the polaroid, the intensity of emergent plane polarised light will be

1. 2a²

2. √2 a²

3. a² / √2

4. a²

Q. Unpolarised light is incident from air on a plane surface of a material of refractive index ${}^{\prime }{\mu }^{\prime }$. At a particular angle of incidence ${}^{\prime }{i}^{\prime }$, it is found that the reflected and refracted rays are perpendicular to each other. Which of the following options is correct for this situation?

1. $i={\sin }^{-1}\left(\frac{1}{\mu }\right)$
2. Reflected light is polarised with its electric vector parallel to the plane of incidence
3. Reflected light is polarised with its electric vector perpendicular to the plane of incidence
4. $i=ta{n}^{-1}\left(\frac{1}{\mu }\right)$

Q. Unpolarized light of intensity $I_0$ passes through an ideal polarizer $A$. Another identical polarizer $B$ is placed behind $A$. The intensity of light beyond $B$ is found to be $\frac{I_0}{2}$. Now, another identical polarizer $C$ is placed between $A$ and $B$. The intensity beyond $B$ is now found to be $\frac{1}{8}.$ The angle between polarizer $A$ and $C$ is,

1. ${60}^{\circ }$
2. $0^{\circ }$
3. ${30}^{\circ }$
4. ${45}^{\circ }$

Q. In a series of polaroids placed in such a way that the optical axis of each polaroid makes the same angle with the next one. When unpolarized light falls on first and if no light is coming out from the last polaroid, then by using how many number of polaroids in series this can be achieved?

1. $3$
2. $4$
3. $5$
4. $6$

Q. Unpolarized light of intensity $32{\text{W m}}^{-2}$ passes through three polarizers such that transmission axis of first is crossed with third. If the intensity of emerging light is $2{\text{W m}}^{-2}$, what is the angle between the transmission axes of the first two polarizers?

1. ${30}^{\circ }$
2. ${60}^{\circ }$
3. ${22.5}^{\circ }$
4. ${45}^{\circ }$

Q.

Two light waves of the same frequency and constant phase difference have intensities in the ratio 81:1. When these waves are superposed, they produce inerference fringes. Calculate the ratio of maximum to minimum intensity

Q. A small plane perfectly reflecting mirror of area $A$ and mass $M$ is hanging vertically with the help of a massless string of length $l$. Light of intensity $I$ is incident horizontally on it. Find the angle made by the string with the vertical.

1. $\frac{IA}{Mg}$
2. $\frac{2IA}{cg}$
3. $\frac{2IA}{cMg}$
4. $\frac{IA}{cMg}$

Q.

What is polarization ratio?

Q. Unpolarized light of intensity $32{\text{Wm}}^{-2}$ passes through three polarizers such that transmission axes of the first and second polarizer makes an angle ${30}^{\circ }$ with each other and the transmission axis of the last polarizer makes an angle $\theta$ with the axis of second polarizer as shown in figure. The intensity of final emerging light will be-

1. $32{\text{Wm}}^{-2}$
2. $16{\text{Wm}}^{-2}$
3. $12{\text{Wm}}^{-2}$
4. $3{\text{Wm}}^{-2}$

Q. Q. Experimental observations have shown that X-rays (i) travel in vacuum with a speed of 3×10^8m/s , (ii) exhibit the phenomenon of diffraction and can the polarized. What conclusion can be drawn about the nature of X -rays from each of these observations?

Q. Unpolarized light with an intensity of $I_0=16\frac{W}{m^2}$ is incident on a pair of polarizers. The first polarizer has its transmission axis aligned at ${50}^{\circ }$ from the vertical. The second polarizer has its transmission axis aligned at ${20}^{\circ }$ from the vertical.

What is the intensity of the light when it emerges from the second polarizer?

1. $4\frac{W}{m^2}$
2. $8{\cos }^2{20}^{\circ }\frac{W}{m^2}$
3. $6\frac{W}{m^2}$
4. $12\frac{W}{m^2}$

Q. When an unpolarised light is polarized, then the intensity of light of the polarized wave :

1. remains the same
2. gets doubled
3. gets halved
4. depends on the colour of the light.

Q. Two polaroids $P_1$ and $P_2$ are placed with their pass axes perpendicular to each other. Unpolarised light of intensity $I_0$ is incident on $P_1$. A third Polaroid $P_3$ is kept in between $P_1$ and $P_2$ such that its pass axis makes an angle of 30${}^o$ with that of $P_1$. Determine the intensity of light transmitted through $P_1,P_2$ and $P_3$.

Q. Two polaroids are kept crossed to each other. Now one of the polaroids is rotated through an angle ${45}^0$. The percentage of incident light now transmitted through the system is:

1. 15%
2. 50%
3. 60%
4. 25%

Q. Two polaroids are crossed. If now one of them is rotated through ${30}^0$ and unpolarised light of intensity $I_0$ is incident on the first polaroid, then the intensity of transmitted light will be

1. $\frac{I_0}{4}$
2. $\frac{3I_0}{4}$
3. $\frac{3I_0}{8}$
4. $\frac{I_0}{8}$

Q. State clearly how an unpolarised light gets linearly polarised when passed through a polaroid.
(i) Unpolarised light of intensity $I_0$ is incident on a polaroid $P_1$ which is kept near another polaroid $P_2$ whose pass axis is parallel to that of $P_1$. How will the intensities of light, $I_1$ and $I_2$, transmitted by the polaroids $P_1$ and $P_2$ respectively, change on rotating $P_1$ without disturbing $P_2$?
(ii) Write the relation between the intensities $I_1$ and $I_2$.

Q. In Young's double slit experiment the slits are of different lengths and widths. The amplitude of the light waves is directly proportional to the :

1. length of the slits
2. distance between the slits
3. area of the slits
4. width of slits

Q. Explain the following, giving reasons:
(i) when monochromatic light is incient incident on the surface seperating two media, the reflected and refracted light both have the same frequency as the incident frequency.
(ii) when light travels from rarer to denser medium, speed decreases. does the decrease in speed imply reduction in the energy carried by the wave?
(iii) in the wave picture of light, intensity if light is determined by the square of the amplitude of the wave. what determines the intensity in the photon picture of light?