CBSE Physics Optics Expected Questions : Unit VIII
[Derivation Type/Numerical Problems-3 Marks]
1. Draw a labelled diagram of an astronomical telescope forming the final image at near object. Write down the formula for its magnifying power.
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2. For Young’s double slit experiment, the slits are separated by 0.24 mm. The screen is 1.2 m away from the slits. The fringe width is 0.3 cm. Calculate the wavelength of light used in (he experiment.
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3. An object is placed at 0.05 m from concave mirror of focal length 0.1 m. Determine the position of image.
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4. Light of wavelength 5,500 A falls on a slit of width 0.13 cm at normal incidence. Calculate the width of central maximum on a screen kept 25 m away from the slit.
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5. An object is placed at a distance of 0 • 2 m from a concave lens of focal length 0 -15 m. Calculate the position of image.
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6. Two thin lenses of focal length -f 10 cm and -5 cm are kept in contact. What is its (/) focal length, (ii) Power of the combination.
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7. Derive the relation between refractive index of a medium and its critical angle,
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8. An object is kept at 0.2 m from a convex lens of focal length 0 • 15 m. Find the position of image produced.
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9. What is the effect on interference fringes in Young’s double slit experiment due to each of following operation ? Give reasons with your answer.
(i) separation between two slits is increased.
(ii) monochromatic source is replaced by a source of white light.
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10. Consider interference between two sources of intensities I and 41. Obtain the intensity at a point where phase difference isJc/2.
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11. Differentiate between luminance and illuminance of a surface.
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12. Two coherent sources where intensity ratio is 81:1 produce interference fringes. Calculate the ratio of intensity of maxima and minime in fringe system.
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13. Two coherent sources whose intensity ratio is 64:1 produces interference, fringes on the screen. Find the ratio of intensity of maxima and minima in the fringe system.
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14. A ray incident normally on one face is totally reflected. What can you conclude about the minimum value of reflection of glass ?
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15. Explain why white light is dispersed when passing through a prism.
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16. What is the total internal reflection ? Define critical angle and find the relation with refractive index.
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17. Red light of wavelength 750 mm enters a glass plate of refactive index 1.5. If the velocity of light
in vacuum is 3 X 108 ms-1 , calculate in glass the (i) frequency, (ii) velocity and (iii) wavelength of light.
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18. The two slits in Young’s experiment are separated by a distance of 0-03 mm. When light of wavelength 5000A falls on the slits an interference is produced 1.5 m away. Find the distance of 4th bright fringe from central maxima.
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19. In a single slit diffraction pattern, how is the angular width of central bright maximum changed, when (i) slit width is decreased.
(ii) the distance between slit and screen is increased, (iii) light of smaller wavelength is used. Justify your answer.
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20. Show by drawing ray diagrams, how a totally reflecting glass prism can be used to deviate a ray of light through(i) 90o; (ii)180°.
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