# Optics question, can anyone confirm my answer?

It_Angel

## Homework Statement

Two converging lenses of focal length=27cm are placed 16.5cm apart. If an object is placed 35cm in front of the first lens, where will the final image be produced? What will be the total magnification?

1/f=1/di+1/do
do2=D-di1
M=-di/do

## The Attempt at a Solution

1/f1=1/di1+1/do1
1/27=1/35+1/di1
di1=118.125cm

do2=D-di1
do2=16.5-116.125
do2=-101.625cm

1/f2=1/do2+1/di2
1/27=1/-101.625+1/di2
di2=21.33cm<<<<<

Mt=M1M2=(-21.33/-101.626)(118.125/35)=0.785X<<<<<

If something is wrong, please show me my mistake, and if it's right please let me know!

Staff Emeritus
Homework Helper

## Homework Statement

Two converging lenses of focal length=27cm are placed 16.5cm apart. If an object is placed 35cm in front of the first lens, where will the final image be produced? What will be the total magnification?

1/f=1/di+1/do
do2=D-di1
M=-di/do

## The Attempt at a Solution

1/f1=1/di1+1/do1
1/27=1/35+1/di1
di1=118.125cm

do2=D-di1
do2=16.5-116.125
do2=-101.625cm

1/f2=1/do2+1/di2
1/27=1/-101.625+1/di2
di2=21.33cm<<<<<

Mt=M1M2=(-21.33/-101.626)(118.125/35)=0.785X<<<<<

If something is wrong, please show me my mistake, and if it's right please let me know!
I agree with your value of di2.

For the magnification, try calculating it again -- I agree with the values 21.33, 101.6, 118.1, and 35, but I get a different final answer.

Also -- again on the magnification -- is M1 positive or negative? How about M2? What does that make Mt?

Hope that helps.

p.s. Welcome to Physics Forums.

It_Angel
Thanks a lot :)