A) the focus shifts to infinity
B) the focal point shirts towards the lens by a small distance
C) the focal point shifts away from the lens by a small distance
D) the focus remains undisturbed
Correct Answer: A
Solution :
The combined focal length of plano-convex lens \[{{T}_{n}}=2{{T}_{i}}\] Hence, \[{{T}_{n}}={{T}_{i}}-T\] (for plane surface), \[{{T}_{n}}={{T}_{i}}+T\] (say) \[\beta \] \[\Omega \] \[\Omega \] \[\Omega \] Now, when concave lens of same focal length is joined to first lens, then combined focal length \[\Omega \] \[\Omega \] \[\phi \] \[\phi ={{\phi }_{0}}+4t\] \[\phi \] Thus, the image can be focussed on infinity \[{{\phi }_{0}}\] or focus shifts to infinity.
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