# Lens question

## Homework Statement

the question is attached

## The Attempt at a Solution

ok so a and b i can do but c), i donts know whether my answer is right and im a little confused about the conceptual idea...

so first thing i did was found the radius of curvature using the lens maker equ using the original setup in air...this i found to be 16cm... [note r1 = -r2]

next i found the focal length in the water situation (i know it doesn't ask for it but still)...this i found to be -81.8cm...
this confuses me cause i thought that only concave lens had negative focal lengths and this is a concave lens...also can the focal length be greater than the radius in a lens? i think it can but cant find anywhere that confirms this...

now to find the image distance s' ...... 1/f = 1/s + 1/s'

i got s' = -37.73cm

then magnification i can do but is what ive done ok?
also can you have a diverging lens that is concave if the object is infront of the focal length? cause that is the only reason that i can think for the focal length to be negative...

Last edited:

ok i just drew the ray diagram and my image was on the same side as the object which agrees with the negative sign for the s'...but the image is further away than the focal point

see attached

#### Attachments

• rr4.jpg
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ive figured it out so no need to answer