Determine image distance relative to lens

phys62

1. The problem statement, all variables and given/known data
Two identical diverging lenses are separated by 13 cm. The focal length of each lens is -6.5 cm. An object is located 3.0 cm to the left of the lens that is on the left. Determine the final image distance relative to the lens on the right.


2. Relevant equations
1/i + 1/o = 1/f

1/i = 1/f - 1/o

3. The attempt at a solution
1/i = 1/-6.5 - 1/3
i= -.487

13 + .487 = 13.487 cm

I feel like I'm not doing this right at all.. can someone please let me know if I'm even on the right track?

rl.bhat

13 + .487 = 13.487 cm
This is the object distance for the second lens. Find the final image distance from the second lens.

phys62

Ok so I took 1/13.487 + 1/i = 1/-6.5

and I solved for i and got -4.386 cm.

Is this correct, or should I have used -13.487 and got -12.547 as my answer?

rl.bhat

and I solved for i and got -4.386 cm.
This is correct.

phys62

It's telling me that answer is incorrect.. I guess I'll try the -12.547 next

rl.bhat

1/i = 1/-6.5 - 1/3
i= -.487
Check this calculation.