Two identical plano-convex lenses can be combined in three ways, as shown. The ratio of the focal lengths of these combinations will be

2 : 2 : 1
1 : 1 : 1
1 : 2 : 2
2 : 1 : 1

Question

Two identical plano-convex lenses can be combined in three ways- as shown- The ratio of the focal lengths of these combinations will be2 - 2 - 11 - 1 - 11 - 2 - 22 - 1 - 1

Toppr Admin · Accepted Answer

In each case the equivalent focal length is given by-xA0-1F-1f-1f-2f-xA0- F-f2so-the ratio will be 1-1-1-hence-option B is correct-

Two identical plano-convex lenses can be combined in three ways, as shown. The ratio of the focal lengths of these combinations will be2 : 2 : 11 : 1 : 11 : 2 : 22 : 1 : 1

In each case the equivalent focal length is given by 1F=1f+1f=2f F=f2so,the ratio will be 1:1:1.hence,option B is correct.

Two identical plano-convex lenses can be combined in three ways, as shown. The ratio of the focal lengths of these combinations will be

2 : 2 : 1
1 : 1 : 1
1 : 2 : 2
2 : 1 : 1

In each case the equivalent focal length is given by
$\frac{1}{F} = \frac{1}{f} + \frac{1}{f} = \frac{2}{f}$
$F = \frac{f}{2}$
so,the ratio will be 1:1:1.
hence,option B is correct.