Saved Bookmarks
| 1. |
1. An object of size 9 cm is placed at 20 cm in front of a concave mirror of focal length15 cm. At what distance from the mirror should a screen be placed, so that a sharp focussedimage can be obtained? Find the size and the nature of the image. |
Answer» Answer :Position of object = 9cm Distance of object = 20cm FOCAL length = 15cm Type of mirror : concave We have to find position of object and HEIGHT of image ★ Focal length of concave mirror is taken negative and that of convex mirror is taken positive. Position of image can be measured by using mirror formula.
u denotes position of object v denotes position of image f denotes focal length By substituting the values, we get ➝ 1/(-20) + 1/v = 1/(-15) ➝ 1/v = -1/15 + 1/20 ➝ 1/v = (-4 + 3)/60 ➝ v = -60 cm There for screen should be placed at 60cm in FRONT of mirror in ORDER to get sharp focussed image. Formula of magnification is given by ➝ m = -v/u = h'/h
➝ -(-60)/(-15) = h'/9 ➝ -4 = h'/9 ➝ h' = -36 cm Negative sign indicates that image is real and inverted. Nature : Real, inverted and enlarged |
|