39. The Brewsters angle $i_b$ for an interface should be :

38. Assume that light of wavelength 600 nm is coming from a star. The limit of resolution of telescope whose objective has a diameter of 2 m is :

37. Angular width of the central maxima in the Fraunhofer diffraction for λ = 6000Å is $θ_0$. When the same slit is illuminated by another monochromatic light, the angular width decreases by 30%. The wavelength of this light is :

36. Unpolarised light is incident from air on a plane surface of a material of refractive index ’ μ ’. At a particular angle of incidence ’ i ’, it is found that the reflected and refracted rays are perpendicular to each other. Which of the following options is correct for this situation ?

35. Two Polaroids $P_1$ and $P_2$ are placed with their axis perpendicular to each other. Unpolarised light $I_0$ is incident on $P_1$. A third polaroid $P_3$ is kept in between $P_1$ and $P_2$ such that its axis makes an angle 45° with that of $P_1$. The intensity of transmitted light through $P_2$ is ?

34. The ratio of resolving powers of an optical microscope for two wavelengths λ1 = 4000Å and λ2 = 6000Å is ?

33. In a diffraction pattern due to a single slit of width ’ a ’, the first minimum is observed at an angle 30° when light of wavelength 5000Å is incident on the slit. The first secondary maximum is observed at an angle of :

32. For a parallel beam of monochromatic light of wavelength ’ λ ’, diffraction is produced by a single slit whose width ’ a ’ is of the wavelength of the light. If ’ D ’ is the distance of the screen from the slit, the width of the central maxima will be :

31. At the first minimum adjacent to the central maximum of a single-slit diffraction pattern, the phase difference between the Huygen’s wavelet from the edge of the slit and the wavelet from the midpoint of the slit is :

30. A beam of light of λ = 600 nm from a dis- tant source falls on a single slit 1 mm wide and the resulting diffraction pattern is observed on a screen 2 m away. The distance between first dark fringes on either side of the central bright fringe is:

29. A parallel beam of fast moving electrons is incident normally on a narrow slit. A fluorescent screen is placed at a large distance from the slit. If the speed of the electrons is increased, which of the following statements is correct ?

28. A parallel beam of light of wavelength λ is incident normally on a narrow slit. A diffraction pattern is formed on a screen placed perpendicular to the direction of the incident beam. At the second minimum of the diffraction pattern, the phase difference between the rays coming from the two edges of slit is ?

27. The angular resolution of a 10 cm diameter telescope at a wavelength of 5000Å is of the order of ?

26. A paper, with two marks having separation d, is held normal to the line of sight of an observer at a distance of 50 m. The diameter of the eye-lens of the observer is 2 mm. Which of the following is the least value of d, so that the marks can be seen as separate ? The mean wavelength of visible light may be taken as 5000Å ?

25. In a Fresnel biprism experiment, the two positions of lens give separation between the slits as 16 cm and 9 cm respectively. What is the actual distance of separation ?

24. A parallel beam of monochromatic light of wavelength 5000Å is incident normally on a single narrow slit of width 0.001 mm. The light is focussed by a convex lens on a screen placed in focal plane. The first minimum will be formed for the angle of diffraction equal to ?

23. Which of the following phenomenon is not common to sound and light waves ?

22. In Young’s double slit experiment, if the separation between coherent sources is halved and the distance of the screen from the coherent sources is doubled, then the fringe width becomes :

21. In a double slit experiment, when light of wavelength 400 nm was used, the angular width of the first minima formed on a screen placed 1 m away, was found to be 0.2°. What will be the angular width of the first minima, if the entire experimental apparatus is immersed in water ? ( $μ_{water}$ = 4/3)

20. In a Young’s double slit experiment, if there is no initial phase difference between the light from the two slits, a point on the screen corresponding to the fifth minimum has path difference ?

19. In Young’s double slit experiment the separation d between the slits is 2 mm, the wavelength λ of the light used is 5896Å and distance D between the screen and slits is 100 cm. It is found that the angular width of the fringes is 0.20°. To increase the fringe angular width to 0.21° (with same λ and D) the separation between the slits needs to be changed to ?

18. Young’s double slit experiment is first performed in air and then in a medium other than air. It is found that $8^{th}$ bright fringe in the medium lies where $5^{th}$ dark fringe lies in air. The refractive index of the medium is nearly ?

17. The intensity at the maximum in a Young’s double slit experiment is $I_0$. Distance between two slits is d = 5λ, where λ is the wavelength of light used in the experiment. What will be the intensity in front of one of the slits on the screen placed at a distance D = 10 d ?

16. In a double slit experiment, the two slits are 1 mm apart and the screen is placed 1 m away. A monochromatic light wavelength 500 nm is used. What will be the width of each slit for obtaining ten maxima of double slit within the central maxima of single slit pattern ?

15. Two slits in Young’s experiment have widths in the ratio 1 : 25. The ratio of intensity at the maxima and minima in the interference pattern, $I_{max}$⁄$I_{min}$ is :

14. In the Young’s double-slit experiment, the intensity of light at a point on the screen where the path difference is λ is K, ( λ being the wave length of light used). The intensity at a point where the path difference is λ/4, will be :

13. In Young’s double slit experiment, the slits are 2 mm apart and are illuminated by photons of two wavelengths $λ_1$ = 12000Å and $λ_2$ = 10000Å. At what minimum distance from the common central bright fringe on the screen 2 m from the slit will a bright fringe from one interference pattern coincide with a bright fringe from the other ?

12. In Young’s double slit experiment the distance between the slits and the screen is doubled. The separation between the slits is reduced to half. As a result the fringe width :

11. In Young’s double slit experiment carried out with light of wavelength (λ) = 5000Å , the distance between the slits is 0.2 mm and the screen is at 200 cm from the slits. The central maximum is at x = 0. The third maximum (taking the central maximum as zeroth maximum) will be at x equal to ?

10. If yellow light emitted by sodium lamp in Young’s double slit experiment is replaced by a monochromatic blue light of the same intensity :

9. In Young’s experiment, two coherent sources are placed 0.90 mm apart and fringe are observed one metre away. If it produces second dark fringe at a distance of 1 mm from central fringe, the wavelength of monochromatic light used would be ?

8. The Young’s double slit experiment is performed with blue and with green light of wavelengths 4360Å and 5460Å respectively. If x is the distance of 4th maxima from the central one, then :

7. In Young’s double slit experiment, the fringe width is found to be 0.4 mm. If the whole apparatus is immersed in water of refractive index 4⁄3 , without disturbing the geometrical arrangement, the new fringe width will be ?

6. The periodic waves of intensities I1 and I2 pass through a region at the same time in the same direction. The sum of the maximum and minimum intensities is:

5. Colours appear on a thin soap film and on soap bubbles due to the phenomenon of ?

4. Interference was observed in interference chamber where air was present, now the chamber is evacuated, and if the same light is used, a careful observer will see ?

3. Ratio of intensities of two waves are given by 4 : 1. Then the ratio of the amplitudes of the two waves is ?

2. Interference is possible in ?

1. Which one of the following phenomena is not explained by Huygens construction of wavefront?