Question

Q1:

if Place the convex and concave lenses together and put them in the path of the parallel rays.Are the outgoing rays converging, diverging or parallel? What does this tell you about the relationship between the focal lengths of these two lenses (I think it will be parallel , but I don't know how to explain it)

Q2:

Slide the convex and concave lenses apart by a few centimeters and observe the effect. Then reverse the order of the lenses. Trace at least one pattern of this type. What is the effect of changing the distance between the lenses? What is the effect of reversing their positions?

THANKS

Answer 1

if you combine the convex and concave it may or may not produce the paralle rays as out come. It purely depends upon the focal lengths of the two lenses.

If both are not of same focal lengths then one may converge more than the divergence created by the second one. further, the rays fall on the first lens are incident normally and on converging/diverging from the first lens it is not in perpendicular to other lens otherwise on combination it will give parallel rays.

if you place certain distance between two lenses then the effective focal length is equal to 1/f1+1/f2-d/(f1*f2)

If both lenses are of same F then first two terms will cancel with each other and the last term is positive only because already one negative is there and one of the f is negative finally it act as converging. if you increase the distance then effective focal length will reduced.

even if you reverse the positions there is no variation,