# Optics question, can anyone confirm my answer?

• It_Angel
And I got 0.785X as my answer for magnification and I think it should be positive since the final image is real and upright. So, Mt should also be positive. Did I make any mistake?In summary, two converging lenses with focal length of 27cm and placed 16.5cm apart have an object placed 35cm in front of the first lens. The final image is produced at 21.33cm and the total magnification is 0.785X. The final image is real and upright, making the magnification positive.

## 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!

It_Angel said:

## 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.

Thanks a lot :)