Hi!(adsbygoogle = window.adsbygoogle || []).push({});

I have 2 problems that I need some help with, plz.

1) How far from a 50mm focal length lens, such as used in many 35mm cameras, must an object be positioned if it is so to form a real image magnified by a factor of 3?

how do i solve for this? I have tried to solve using lens equation but not the answer I would expect, my answer is 52mm. Is this correct if not how did you go about solving for this?

2) A biconvex lens is formed by using a piece of plastic(n=170). the radius of the front surface is 20cm and the radius of the back surface is 30cm. what is the focal length of the lens?

I know that r/2 = f but should i add both radius's and use that /2? I need some help?

Thanks!

Dx

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Light: Goemetric Optics

**Physics Forums | Science Articles, Homework Help, Discussion**