

InterviewSolution
Saved Bookmarks
1. |
A concave mirror gives a real image magnifies 4 times. When the object is moved 3 cm the magnification of the real image is 3 times. Find the focal length of mirror. |
Answer» We know that, ` m=(v)/(u)=(f)/(u-f)` In first case, ` (f)/(u-f)=4` `F=4u-4f` and `5f=4u` In `2^(nd)` case, `(f)/((u+3)-f)=+3` `F=3u+9-3f` `:. 4u-4f=3u+9-3f` `u=f+9=(4u)/(5)+9` `u=45 cm` and `f=36 cm` |
|