# Homework Help: Ray tracing for convex lens

1. Nov 27, 2014

### toothpaste666

1. The problem statement, all variables and given/known data
B) Is the image real or virtual? Explain.
C) Using the lens equation, find the image distance.

2. Relevant equations

1/di + 1/do = 1/f

3. The attempt at a solution
A)

B) The image is real because it is on the opposite side of the lens as the source of light.

C) do = 6cm f = 3cm
1/do + 1/di = 1/f
1/di = 1/f - 1/do
1/di = do/f(do) - f/f(do)
1/di = (do-f)/(f*do)
di = (f*do)/(do-f) = (3cm * 6cm)/(6cm - 3cm) = (18cm^2)/(3cm) = 6cm
di = 6cm

2. Nov 27, 2014

### toothpaste666

not too confident about my ray tracing. this is what it shows in the book but i know it differs depending on the situation

3. Nov 28, 2014

### ehild

Your ray tracing is all right. The ray entering parallel with the axis goes through the focus on the other side of the lens.
The ray entering through the focus, goes parallel with the axis on the other side.

4. Nov 28, 2014

### toothpaste666

ok i feel a little more confident that i got both of these problems right. thanks for the help

5. Nov 28, 2014

### ehild

you are welcome.:)