Saved Bookmarks
| 1. |
A small candle, 2.5 cm in size is placed at 27 cm in front of a concave mirror of radius of curvature 36 cm. At what distance from the mirror should a screen be placed in order to obtain a sharp image? Describe the nature and size of the image. If the candle is moved closer to the mirror, how would the screen have to be moved? |
|
Answer» Solution :Here, h=2.5 cm, `mu=-27 cm, R =-36 cm`. As per mirror formula `1/v + 1/u = 1/f = 2/R`, we have `1/v =1/f -1/u =2/R -1/u =2/(-36) -1/(-27) =-1/18 + 1/27 = -1/54 rArr v=-54 cm` Thus screen should be placed at a distance of 54 cm from the mirror in ORDER to obtain a sharp IMAGE of the candle. As `m=h./h =-v/u`, hence size of image `h. =-v/u. h =-(-54)/(-27) xx 2.5 = 5 cm` Thus, the image is real, MAGNIFIED and inverted image. If the candle is MOVED closer to the mirror, the screen has to be moved away from the mirror. In fact as `u lt f, v to infty`. However, if `u lt f` However, if `u lt f` then image formed is virtual and cannot be obtained on the screen. |
|