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 ?