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

`240 cm` ; `34.3 cm`

Explanation

`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`