Question

3 lenses L1 L2 and L3 each of focal length 30 cm are placed coaxially as shown in figure and an object is held at 60 cm from the optic centre of lens Alvin the final real images formed at the focus of L3 calculate the separation between L1 and L2 and L2 and L3

Answer 1

Answer:

For lens l1,u=−60cm,f=+30cm.

If v1 is distance of image I1 from C1, then from

1v1−1u=1f1

1v1=1f1+1u=130−160=160

v1=60cm=C1I1

As final image I is at focus of L3, therefore, rays falling on L3 must be parallel to common principal axis. For this to happen, I1 must be at the focus of L2. Hence distance between L1L2 is

=C1C2=C1I1+I1C2=60cm+30cm=90cm

and distance between L2andL3 can have any reasonable value, as rays between L2 and l3 are parallel rays

Explanation:

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