Question

Short Answer Type Questions 11. An object is placed at a distance of 10 cm from a concave mirror of focal length 20 cm. (a) Draw a ray diagram for the formation of image. (b) Calculate the image distance. (c) State two characteristics of the image formed. 12. If an object of 10 cm height is placed at a distance of 36 çm from a concave mirror of focal length 12 cm, find the position, nature and height of the image. 13. At what distance from a concave mirror of focal length 10.cm should an object 2 cm long be placed in order to get an erect image 6 cm tall ? 14. When an object is placed at a distance of 15 cm from a concave mirror, its image is formed at 10 cm in front of the mirror. Calculate the focal length of the mirror. 15. An object 3 cm high is placed at a distance of 8 cm from a concave mirror which produces a virtual image 4.5 cm high : (1) What is the focal length of the mirror ? (ii) What is the position of image ? (111) Draw a ray-diagram to show the formation of image. 16. A converging mirror forms a real image of height 4 cm of an object of height 1 cm placed 20 cm away from the mirror : (i) Calculate the image distance. (ii) What is the focal length of the mirror ? 17. An object of size 7.0 cm is placed at 27 cm in front of a concave mirror of focal length 18 cm. At what distance from the mirror should a screen be placed so that a sharp focussed image can be obtained ? Find the size and nature of image. [Hint. Find the value of image distance (v) first. The screen should be placed from the mirror at a distanc equal to image distance).​

Answer 1

Answer:

Explanation:

(b) f = -20cm, u = -10cm, v = ?

We know that

1/v + 1/u = 1/f

⇒ 1/v + 1/(-10) = 1/(-20)

⇒ 1/v = -1/20 + 1/10 = 1/20

∴ v = 20 cm

(c) Characteristics of image formed

(i) Image is virtual.

(ii) Image is erect.