Nội dung text 7-light--interference-.pdf
Light & Interference 1. A thin convex lens made from crown glass (μ = 3 2 ) has focal length f. When it is measured in two different liquids having refractive indices 4 3 and 5 3 , it has the focal length f1 and f2, respectively. The correct relation between the focal lengths is : (A) f1 = f2 < f (B) f1 > f and f2 becomes negative (C) f2 > f and f1 become negative (D) f1 and f2 both become negative 2. A beam of light consisting of red, green and blue colours is incident on a right angled prism. The refractive index of the material of the prism for the above red, green blue wavelengths are 1.39,1.44 and 1.47 respectively. The prism will : (A) Not separate the three colours at all (B) Separate the red colour part from the green and blue colours (C) Separate the blue colour part from the red and green colours (D) Separate all the three colours from one another 3. At two point P and Q on screen in Young's double slit experiment, waves from slits S1 and S2 have a path difference 0 and λ 4 respectively. The ratio of intensities at P and Q will be : (A) 3: 2 (B) 2: 1 (C) √2: 1 (D) 4: 1 4. 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 : (A) π radian (B) π 8 radian (C) π 4 radian (D) π 2 radian 5. In an astronomical telescope in normal adjustment a straight black line of length L is drawn on inside part of objective lens. The eye-piece forms a real image of this line. The length of this image is I. The magnification of the telescope is (A) L+I L−I (B) L I (C) L I + 1 (D) L I − 1 6. A breaker contains water up to a height h1 and kerosene of height h2 above water so that the total height of (water + kerosene) is (h1 + h2 ). Refractive index of water is μ1 and that of kerosene is μ2. The apparent shift in the position of the bottom of the beaker when viewed from above is : (A) (1 − 1 μ1 ) h2 + (1 − 1 μ2 ) h1 (B) (1 + 1 μ1 ) h1 + (1 + 1 μ2 ) h2 (C) (1 − 1 μ1 ) h1 + (1 − 1 μ2 ) h2 (D) (1 + 1 μ1 ) h2 − (1 + 1 μ2 ) h1 7. For a parallel beam of monochromatic light of wavelength ' λ ', diffraction is produced by a single slit whose width ' a ' is of the order 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 : (A) Da λ (B) 2Da λ (C) 2Dλ a (D) Dλ a 8. Two identical thin plano-convex glass lenses (refractive index 1.5) each having radius of curvature of 20 cm are placed with their convex surface in contact at the centre. The intervening space is filled with oil of refractive index 1.7. The focal length of the combination is : (A) − 50 cm (B) 50 cm (C) −20 cm (D) −25 cm
9. Statement-I On viewing the clear blue portion of the sky through a Calcite Crystal, the intensity of transmitted light varies as the crystal is rotated. Statement-II The light coming from the sky is polarized due to scattering of sun light by particles in the atmosphere. The scattering is largest for blue light. (A) Statement I is false, Statement II is true (B) Statement I is true, Statement II is false (C) Statement I is true, Statement II is true Statement II is the correct explanation of Statement I (D) Statement I is true, Statement II is true; Statement II is not correct explanation of Statement I 10. The refracting angle of a prism is A, and refractive index of the material of the prism is cot (A/2). The angle of minimum deviation is : (A) 90∘ − A (B) 180∘ + 2 A (C) 180∘ − 3 A (D) 180∘ − 2 A 11. In a double slit experiment, the two slits are 1 mm apart and the screen is placed 1 m away. A monochromatic light of 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? (A) 0.5 mm (B) 0.02 mm (C) 0.2 mm (D) 0.1 mm 12. A green light is incident from the water to the air- water interface at the critical angle ( θ ). Select the correct statement. (A) The entire spectrum of visible light will come out of the water at an angle of 90∘ to the normal (B) The spectrum of visible light whose frequency is less than that of green light will come out of the air medium (C) The spectrum of visible light whose frequency is more than that of green light will come out to the air medium. (D) The entire spectrum of visible light will come out of the water at various angles to the normal 13. In the Young's double slit experiment, the intensity of light at a point on the screen where the path difference λ is K, ( λ being the wavelength of light used). The intensity at a point where the path difference is λ/4 will be : (A) K (B) K/4 (D) K/2 (D) zero 14. Let the x − y plane be the boundary between two transparent media. Medium 1 in z ≥ 0 has a refractive index of √2 and medium 2 with z < 0 has refractive index of √3. A ray of light in medium 1 given by the vector A⃗ = 6√3iˆ + 8√3jˆ − 10kˆ is incident on the plane of separation. The angle of refraction in medium 2 is : (A) 45∘ (B) 60∘ (C) 75∘ (D) 30∘ 15. If the focal length of objective lens is increased then magnifying power of (A) Microscope will increase but that of telescope decrease (B) Microscope and telescope both will increase. (C) Microscope and telescope both will decrease (D) Microscope will decrease but that of telescope will increase. 16. The angle of a prism is A. one of its refracting surface is silvered. Light rays falling at an angle of incidence 2A on the first surface returns back through the same path after suffering reflection at the slivered surface. The refractive index μ, of the prism is : (A) 2sin A (B) 2cos A (C) 1 2 cos A (D) tan A 17. This question has paragraph followed by two statements, Statement I and Statement II. Of the given four alternatives after the statements, choose one that describes the statements. A thin air film is formed by putting the convex surface of a plane-convex lens over a plane glass plate. With monochromatic light, this film gives an interference pattern due to light reflected from the top (convex) surface and the bottom (glass plate) surface of the film. Statement 1 : When light reflects from the air-glass plate interface, the reflected wave suffers a phase change of π. Statement 2: The centre of the interference pattern is dark. (A) Statement 1 is true, Statement 2 is true, Statement 2 is the correct explanation of Statement 1 (B) Statement 1 is true, Statement 2 is true, Statement 2 is not the correct explanation of
Statement 1 (C) Statement 1 is false, Statement 2 is true (D) Statement 1 is true, Statement 2 is false 18. A plano convex lens fits exactly into a plano concave lens. Their plane surfaces are parallel to each other, if lenses are made of different materials of refractive indices μ1 and μ2 and R is the radius of curvature of the curved surface of the lenses, then the focal length of the combination is : (A) R (μ1−μ2 ) (B) 2R (μ2−μ1 ) (C) R 2(μ1+μ2 ) (D) R 2(μ1−μ2 ) 19. For a normal eye, the cornea of eye provides a converging power of 40D and the least converging power of the eye lens behind the cornea is 20D. using this information, the distance between the retina and the cornea-eye lens can be estimated to be : (A) 1.67 cm (B) 1.5 cm (C) 5 cm (D) 2.5 cm 20. A car is fitted with a convex side-view mirror of focal length 20 cm. A second car 2.8 m behind the first car is overtaking the first car at a relative speed of 15 m/s. The speed of the image of the second car as seen in the mirror of the first one is : (A) 1 15 m/s (B) 10 m/s (C) 15 m/s (D) 1 10 m/s 21. A mixture of light, consisting of wavelength 590 nm and an unknown wavelength, illuminates Young's double slit and gives rise to two overlapping interference patterns on the screen. The central maximum of both lights coincide. Further, it is observed that the third bright fringe of known light coincides with the 4th bright fringe of the unknown light. From this data, the wavelength of the unknown light is : (A) 393.4 nm (B) 885.0 nm (C) 442.5 nm (D) 776.8 nm 22. A parallel beam of light of wavelength λ is incident normally on a narrow slit. A diffraction pattern 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 : (A) 2π (B) 3π (C) 4π (D) πλ 23. A ray of light is incident at an angle of incidence I, on one face of a prism of angle A (assumed to be small) and emerges normally from the opposite face. If the refractive index of the prism is μ, the angle of incidence I, is nearly equal to : (A) μA (B) μA 2 (C) A μ (D) A 2μ 24. Two beams, A and B of plane polarized light with mutually perpendicular planes of polarization are seen through a Polaroid. From the position, when the beam A has maximum intensity (and beam B has zero intensity), a rotation of Polaroid through 30∘ makes the two beams appear equally bright. If the initial intensities of the two beams are IA and IB respectively, then IA/IB equals : (A) 3 (B) 3/2 (C) 1 (D) 1/3 25. A student measures the focal length of a convex lens by putting an object pin at a distance u from the lens and measuring the distance v of the image pin. The graph between u and v plotted by the student should look like : (A) (B)
(C) (d) 26. A concave mirror of focal length f1 is placed at a distance of d from a convex lens of focal length f2. A beam of light coming from infinity and falling on this convex lens -concave mirror combination returns to infinity. The distance d must equal : (A) f1 + f2 (B) − f1 + f2 (C) 2f1 + f2 (D) − 2f1 + f2 27. In an optics experiments, with the position of the object fixed, a student varies the position of a convex lens and for each position; the screen is adjusted to get a clear image of the object. A graph between the object distance u and the image distance v, from the lens, is plotted using the same scale for the two axes. A straight line passing through the origin and making an angle 135∘ with the x-axis meets the experimental curve at P. The magnitude of the coordinates of P will be: (A) (2f, 2f) (B) ( f 2 , f 2 ) (C) (f, f) (D) (4f, 4f) 28. For the angle of minimum deviation of a prism to, be equal to its refracting angle, the prism must be made of a material whose refractive index: (A) Lies between √2 and 1 (B) lies between 2 and √2 (C) is less than 1 (D) is greater than 2 29. A biconvex lens has a radius of curvature of magnitude 20 cm. which one of the following options describe best the image formed of an object of height 2 cm placed 30 cm from the lens ? (A) Virtual, upright, height = 1 cm (B) Virtual, upright, height = 0.5 cm (C) Real, inverted, height = 4 cm (D) Real, inverted, height = 1 cm 30. A transparent sold cylinder rod has a refractive index of 2 √3 . It is surrounded by air. A light ray is incident at the mid point of one end of the rod as shown in the figure. The incident angle θ for which the light ray grazes along the wall of the rod is : (A) sin−1 ( 1 2 ) (B) sin−1 ( √3 2 ) (C) sin−1 ( 2 √3 ) (D) sin−1 ( 1 √3 ) 31. A thin prism of angle 15∘ made of glass of refractive index μ1 = 1.5 is combined with another prism of glass of refractive index μ2 = 1.75. The combination of the prisms produces dispersion without deviation. The angle of the second prism
English