CBSE Physics Optics Expected Questions : Unit VIII
[Long Answer Type Questions—5 Marks Questions)
1. Draw a ray diagram to show the formation of the image of an object placed between the optical centre and focus of the convexlens. Obtain relation between the object distance u, image distance v and focal length/ for the particular case for given convex lens. State clearly the assumptions and sign conventions used.
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2. A concave mirror and a concave lens are held in water. What changes if any do you expect in their respective focal lengths as compared to their values in air ?
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3. You are given two convex lenses of focal length 80 mm and 800 mm. Which one will you use as an objective and which one as eye piece for constructing astronomical telescope ? Trace the course of rays through the two lenses to show the formation of final image of a distant object. Derive an expression for the magnifying power of the telescope in the normal adjustment.
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4. An object 0-04 m high is placed at a distance of 0-8 m from a concave mirror of radius of curvature 0-4 m. Find the position, nature and the size of the image formed.
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5. An object 0.05 m high is placed at a distance of 0.5 m from a convex mirror of radius of curvature 0.2 m. Find the position, nature and the size of the image formed.
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6. An object is kept in front of a concave mirror of focal length 20 cm. The image formed is three times the size of the object. Calculate two possible distances of ihe object from the mirror.
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7. Find the ratio of intensities of two points x and y on a screen in Young’s double slit experiment,
where waves from s1, and s2 has path difference of (i) 0 and (ii) A/4.
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8. Derive the expression for the angle of deviation for a ray of light passing through an equilateral prism of reflecting angle A.
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9. What is dispersion of .light ? With the help of a diagram, explain the construction of a spectro¬scope. How can it be used to determine refractive index of material of a prism ?
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10. Describe an experiment to show that light waves are transverse in nature.
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11. With the help of a ray diagram, explain the principle working of a compound microscope.
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12. Derive the angular separation between central maxima and first order maxima of diffraction pattern due to a single slit of width 0.25 mm when light of wavelength 5890A is incident on it normally.
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13. Define magnifying and resolving power for a telescope The objective of an astronomical telescope has a diameter of 150 mm and focal length 4 m. The eye piece has’a focal length 250 mm. Calculate its resolving and magnifying powers. What is distance between objective and eye-piece ? Take average wavelength of light to be 6,000 A.
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14. With the help of a ray diagram explain the phenomenon of total internal reflection. The reflecting angle of a glass prism is 60°. The value of minimum deviation for light passing through prism is 40°. Calculate the value of refractive index of the material of the prism. Given sin 50° = 0.766.
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