# Magnification of an Image formed by a converging lens

• fordy314

## Homework Statement

A converging lens with a focal length of 14.2 cm is used to inspect a coin. The lens forms a virtual image 30.1 cm away. What is the magnification?

## Homework Equations

(1/Si) + (1/So) = (1/f)
M = (hi/ho) = (-Si/So)

## The Attempt at a Solution

1/So = 1/f - 1/Si

1/(1/So) = So = 26.88cm

M = (-Si/So) = -30.1/26.88 = 1.12

I'm pretty sure that I have the solution and answer correct, but I just wanted to double check. This homework is online and the site is telling me that I have the answer wrong and I just wanted to make sure that I wasn't missing anything before I bother my teacher about it. As of right now I think it's just an error in the code of the site, but I'm just double checking. Thanks.

## Homework Statement

A converging lens with a focal length of 14.2 cm is used to inspect a coin. The lens forms a virtual image 30.1 cm away. What is the magnification?

Have you accounted for the fact that it's a virtual image?

## Homework Statement

A converging lens with a focal length of 14.2 cm is used to inspect a coin. The lens forms a virtual image 30.1 cm away. What is the magnification?

## Homework Equations

(1/Si) + (1/So) = (1/f)
M = (hi/ho) = (-Si/So)

## The Attempt at a Solution

1/So = 1/f - 1/Si

1/(1/So) = So = 26.88cm

M = (-Si/So) = -30.1/26.88 = 1.12

I'm pretty sure that I have the solution and answer correct, but I just wanted to double check. This homework is online and the site is telling me that I have the answer wrong and I just wanted to make sure that I wasn't missing anything before I bother my teacher about it. As of right now I think it's just an error in the code of the site, but I'm just double checking. Thanks.

This object [the coin] is placed inside the focus [giving a virtual image] so some/all of those distances may be negative.
I am never confident with that (1/Si) + (1/So) = (1/f) formula, so I always use a couple of alternates, and a ray diagram.

Check your notes or your textbook. There are specific rules for deciding on the signs of the various quantities.

Check your notes or your textbook. There are specific rules for deciding on the signs of the various quantities.

Ah, right, I forgot about the signs. Looks like the summer off has made me a little rusty. I just accounted for the signs and got the right answer. Thanks for your help.