Question

A concave convex figure lens made of glas `(mu=1.5)` has surface of radii 20 cm and 60 cm. a. Locate the image ofan object placed 80 cm to the left of the lens along the principal axis. B. A similar lens is placed coaxially at distanc of 160 cm right of it. Locate the position of the image.

Answer 1

Correct Answer - `240 cm ; 34.3 cm`
`R_1 is +, R_2 is +`
`(1)/(f)=(mu - 1)((1)/(R_1) - (1)/(R_2))`
`(1)/(f) = (1.5 - 1) ((1)/(20) - (1)/(60)), f = 60 cm`
(a) Now, `u = - 80 cm, f = 60 cm`
As `(1)/(v)-(1)/(u)=(1)/(f)`
`:. v = 240 cm`
First image `I_1` is at `240 cm` from first lens.
(b) The second lens intercepts the converging beam. Image `I_1` acts as a virtual source for second lens.
`u = 240 - 160 = + 80 cm`
Use `(1)/(v)-(1)/(u)=(1)/(f)`, to get `v = 34.3 cm`.
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