Saved Bookmarks
| 1. |
A plano - convex lens acts like a concave mirror of 28 cm focal length when its plane surface is silvered and like a concave mirror of 10 cm focal length its curved surface is silvered. The refractive index of the material of the lens is : |
|
Answer» 1.55 `(1)/(28)=(2)/(f_(1))+(1)/(f_(m))=(2)/(f_(1))"" ...(1)` `Case II : (1)/(10)=(2)/(f_(1))=(2)/(f_(m)) "" ...(2)` where `f_(m)` = FOCAL length of curved SILVERED hence `f_(m) = (R)/(2)` where R = radius of curvature of curved surface. (By subtracting eqns. (1) from (2) `(1)/(f_(m)) = (1)/(10) - (1)/(28) RARR f_(m) = (140)/(9) cm`. |
|