## 26 January 2013

### X(Physics) Assignment for Ch – Light (Reflection and Refraction)

1. An object is placed between two plane mirrors inclined at an angle of 45° to each other. How many images do you expect to see?

2. A convex mirror is held in water. What should be the change in its focal length?
3.If the light from the Sun subtend an angle Q at the pole of a concave mirror of focal length f, where will it converge? Also find the diameter of the image. Draw the necessary ray diagram.
4. When does Snell’s law of refraction fail?
5. How does the frequency of a beam of ultraviolet light changes when it goes from air to glass?
6.State two conditions under which a ray of light suffering refraction from medium 1 to medium 2 does not undergo any change in direction
7.Name the factor on which lateral shift produced by glass slab depends?
8. A glass lens is immersed in water. How is the power of the lens affected?
9. Why is the power of a lens is measured as reciprocal of focal  length? Give reason.
10.A convex lens is made of a material of refractive index m1 when placed in a medium of refractive index m2, behaves as a diverging lens. How are m1 and mrelated?
11. An object is held at a distance of 60 cm from a convex mirror of focal length 20 cm. At what distance from the mirror, should a plane mirror be held so that images in the two mirrors coincide?(ans. 22.5 cm)
12.How do you find the rough focal length of a convex lens? Is the same method applicable to a concave lens?
13. Which factors determine the focal length of a lens?
14. The formula for linear magnification of a spherical mirror is m=h’/h = -v/u. What determines the sign of m? What is the significance of this sign?
15.A convex lens made of material of refractive index n2 is kept in a medium of refractive index n1. A parallel beam of light is incident on the lens. Compare the path of rays of light emerging from the convex lens if
(i) n12  (ii)n1=n2 (iii) n1>n2

16. A concave lens of focal length 25 cm and a convex lens of focal length 20 cm are placed in contact with each other. What is the power of this combination? Also, calculate focal length of this combination. (ans. 1m)
17.  A convergent lens of power 8D is combined with a divergent lens of power -10 D. Calculate focal length of the combination. (ans.-0.5 m)
18.  A concave lens has a focal length of 15 cm. At what distance should an object from the lens be placed so that it forms an image at 10 cm from the lens? Also find the magnification of the lens.
19.  Under what condition in an arrangement of two plane mirrors, incident ray and reflected ray will always be parallel to each other, whatever be the angle of incidence? Show the same with the help of diagram.
20.  How much time will light take to cross 2 mm thick glass pane if refractive index of glass is 3/2?  (ans. 10-11s)
21.  Light travel from rarer medium 1 to a denser medium 2. The angle of incidence and refraction are respectively 45° and 30°. Calculate the refractive index of second medium with respect to the first medium.
22.  A pond of depth 20 cm is filled with water of refractive index 4/3. Calculate apparent depth of the tank when viewed normally.
23.  Light of wavelength 500nm in air enters a glass plate of refractive index 1.5. Find (a)speed. (b)frequency, and (c)wavelength of light in glass. Assume that the frequency of light remains the same in both media.
24.  A myopic person prefers to remove his spectacles while reading a book. Give reason.

25.  A hypermetropic person prefers to remove his spectacles while driving a vehicle. Give reason.

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