Answer to Question #171617 in Optics for Siyabonga

Question

Two convex lenses with focal lengths of 30cm are placed 100cm apart. An object is placed 15cm in front of the first lense. Determine the position and magnification of the final image due to both lenses.

Answer 1

Answer

Object is at 15cm from lens First

$\frac{1}{V}=\frac{1}{u}-\frac{1}{f}$

$\frac{1}{V}=\frac{1}{15}-\frac{1}{30}=\frac{1}{30}$

V=30cm

So image of lens first is at 100-30=70cm from lens second

Now for second lens

$\frac{1}{v}=\frac{1}{u}+\frac{1}{f}=\frac{1}{70}+\frac{1}{30}=\frac{1}{21}$

v=21cm

It will be 21cm right of the lens second

Position as above.

Magnification

$M=\frac{-v}{u}=\frac{-21}{15}=-1.4$