optics class 10

 1. A concave lens has focal length of 20 cm. At what distance from the lens a 5 cm tall object is placed so that it forms an image at 15 cm from the lens? Also calculate the size of the image formed.  [3 marks]

2. An object 50 cm tall is placed on the principal axis of a convex lens. Its 20 cm tall image is formed on the screen placed at a distance of 10 cm from the lens. Calculate the focal length of the lens. [3 marks]

3. Draw the ray diagram in each case to show the position and nature of the image formed when the object is placed: [5 marks]

(I) at the centre of curvature of a concave mirror

(ii) Between the pole P and focus F of a concave mirror

(iii) In front of a convex mirror
(iv) At 2F of a convex lens                                                                 
(v) In front of a concave lens

_{4. Draw ray diagrams to represent the nature, position and relative size of the image formed by a convex lens for the object placed:
(a) at 2F1
(b) between F1 and the optical centre O of lens: [2 marks]}

_{5.An object 2 cm in size is placed 30 cm in front of a concave mirror of focal length 15 cm. At what distance from the mirror should a screen be placed in order to obtain a sharp image? What will be the nature and the size of the image formed? Draw a ray diagram to show the formation of the image in this case. [5 MARKS]}

_{6.  A convex lens has a focal length of 10 cm. At what distance from the lens should the object be placed so that it forms a real and inverted image 20 cm away from the lens? What would be the size of the image formed if the object is 2 cm high? With the help of a ray diagram show the formation of the image by the lens in this case. [5 marks]}

_{7. (a) It is desired to obtain an erect image of an object, using a concave mirror of focal length 20 cm.(I) What should be the range of distance of the object from the mirror?[5MARKS](ii) Will the image be bigger or smaller than the object?(iii) Draw a ray diagram to show the image formation in this case.
(b) One half a convex lens of focal length 20 cm is covered with a black paper.(I)Will the lens produce a complete image of the object?(ii)Show the formation of image of an object placed at 2F1 of such covered lens with the help of a ray diagram.}

_{8. The refractive index of water is 1.33 and the speed of light in air is 3 x 108 ms-1. Calculate the speed of light in water. [2 marks]}

_{9. In an experiment with a rectangular glass slab, a student observed that a ray of light incident at an angle of 55° with the normal on one face of the slab, after refraction strikes the opposite face of the slab before emerging out into air making an angle of 40° with the normal. Draw a labeled diagram to show the path of this ray. What value would you assign to the angle of refraction and angle of emergence? [5 marks]}

_{10. The image of an object placed at 60 cm in front of a lens is obtained on a screen at a distance of 120 cm from it. Find the focal length of the lens. What would be the height of the image if the object is 5 cm high? [2 marks]}

_{11. Distinguish between a real and a virtual image of an object. What type of image is formed (I) by a plane mirror, (ii) on a cinema screen? [3MARKS]}

_{12. A ray of light travelling in air enters obliquely into water. Does the light ray bend towards or away from the normal? Why? Draw a ray diagram to show the refraction of light in this situation [2 marks]}

_{13. write the application of (4 marks)
a) concave mirror
b) convex mirror    c) plane mirror}