Help With a Difficult Lenses Question: Find the Answer!

[Rheegeaux22]

Homework Statement

The question is : https://postimg.org/image/lntyejfvp/

Homework Equations

1/s +1s' =1/f

The Attempt at a Solution

Hello, I have an upcoming test on Monday on lenses and while reviewing I've come across a question that confused me.

My understanding is that the image of the first lens is used as the object of the second lens. I keep coming up with the answer below.

My solution:
https://postimg.org/image/vqerb9suf/

*The correct answer is 10m

Thank you for helping me. I really need to get a high score in this test to get exempted for the finals. I really don't want to take the finals :(

 

[Andrew Mason]

Welcome to PF Rheegeaux!

What is the focal length of the converging lens?

AM

 

[Cutter Ketch]

Welcome to PF Rheegeaux!

What is the focal length of the converging lens?

AM

Yes, you need the focal length of the converging lens. From the wording of the problem I suspect you were told the focal length of the converging lens in the problem immediately preceeding this one.

In your solution you assumed the focal length of the converging lens is 3m, perhaps guessing they meant to say both lenses are 3. However when you look back st the previous problem I bet you will find the focal length is 2 which will fix the discrepancy.

 

[Rheegeaux22]

Yes, you need the focal length of the converging lens. From the wording of the problem I suspect you were told the focal length of the converging lens in the problem immediately preceeding this one.

In your solution you assumed the focal length of the converging lens is 3m, perhaps guessing they meant to say both lenses are 3. However when you look back st the previous problem I bet you will find the focal length is 2 which will fix the discrepancy.

Thanks :), you're right the focal length is 2.