Important Questions for Board Exam: Check Your Knowledge
1. Magnification of plane mirror is + 1. What does it indicate ?
2. A real image, 1/5 th size of object is formed at a distance of 18 cm from a mirror. What is the nature of the mirror ?Calculate its focal length.
3. Name the type of mirror used in the following and reason for using it :
(a) Solar furnace
(b) Rear view mirror in a vehicle
4. What should be the position of the object, when a concave mirror is used :
(a) as a shaving mirror ?
(b) in torches as reflecting mirror ?
5. (a) Define principal focus of a spherical mirror.
(b) For what position of the object does a concave mirror form a real, inverted and diminished image of the object ? Draw the ray diagram.
(c) An object 4 cm high is placed at a distance of 6 cm in front of a concave mirror of focal length 12 cm. Find the position of the image.
6. For what position of an object, a concave mirror forms a real image equal to size of object ?
7. Identify the nature of mirror and mention two characteristics of image formed when magnification m = + 6.
8. Suggest a method to find approximate focal length of a concave mirror.
9. Draw ray diagram when :
(a) object is placed between pole and focus of a concave mirror.
(b) object is placed at infinity from a convex mirror.
10. Name the type of spherical mirror which
(a) has positive focal length.
(b) always forms a virtual image.
IMPORTANT QUESTIONS FOR BOARD EXAMS CLASS X :CHECK YOUR KNOWLEDGE
1. Refractive indices of medium A, B and C are 1.3, 1.5 and 1.4 respectively.
In which of the following the speed of light will be the :
(a) fastest ?
(b) slowest ?
2. A compound lens is made up of two thin lenses having power + 12.5 D and – 2.5 D. Find the focal length and power of the combination.
3. Light enters from air to kerosene having a refractive index of 1.47. What is the speed of light in kerosene ?
4. A 5 cm tall object is placed perpendicular to principal axis of a convex lens of focal length 10 cm. If the object is placed 30 cm away from the lens, find the position, size and nature of image.
5. One half of a convex lens is covered with black paper.
(a) Show the formation of image of a object placed at 2F, of such covered lens with the help of ray diagram. Mention the position and nature of the image.
(b) Draw the ray diagram for same object at same position in front of the same lens, but now uncovered. Will there be any difference in image obtained in the two cases ? Give reasons for your answers.
6. A thin converging lens forms a (i) real magnified image, (ii) virtual magnified image.
(a) Write the position of object in each case.
(b) Draw labelled diagram for each case.
7. (a) What happens to a ray of light when it travels from one medium to another having equal refractive indices ?
(b) State the cause of refraction of light.
8. (a) Define 1 dioptre of power. Find the focal length of a lens of power – 2.0 D.
(b) Why does a lemon kept in water in a glass tumbler appear to be bigger than actual size ?
9. A ray travelling in water enters obliquely into glass. Does the light bend towards or away from the normal and why ?
10. An object is placed at the focus of a convex lens. Draw ray diagram to locate the position of image formed.
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