Combination of thin lens and concave mirror

AI Thread Summary
The discussion revolves around solving a problem involving a thin converging lens and a concave mirror, where the participant initially struggles with determining the correct image distance. They question whether the last object distance should be negative, given the conventions for distances in optics. Several contributors point out issues with the problem's formulation, including the missing refractive index of the lens and the incorrect reference to multiple focal points for the concave mirror. Ultimately, the participant resolves their confusion by realizing the last object distance should be considered positive. The conversation highlights the importance of clarity and completeness in physics problems.
physstudent189
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Homework Statement
The figure below shows a thin converging lens for which the radii are R1 = 8.48 cm and R2 = -11.4 cm. The lens is in front of a concave spherical mirror of radius R = 6.07 cm. If its focal points F1 and F2 are 4.58 cm from the vertex of the lens: b) If the lens and mirror are 20.3 cm apart and an object is placed 8.00 cm to the left of the lens, determine the position of the final image relative to the lens (Positive values are to the left).
Relevant Equations
1/f = 1/do + 1/di
I created the following ray diagram to help me solve the problem:
PLQ and CAPA.jpg

Then I applied the mirror equation 3 separate times.
IMG_8003F46351DC-1.jpeg

However, the final image distance I got is wrong. I'm wondering if I'm mistaken in taking the last object distance to be negative. However I only have one more try to get this right so I really want to make sure I'm approaching it from the right angle. I thought the last image distance would be negative because it is distance behind the converging lens, and we are told in the question that distances to the left of the lens (in front) are positive. I really appreciate any help or pointers anyone can give. Thank you!
 
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nevermind I got it! Had to take the last obj. dist. as positive :-)
 
physstudent189 said:
Homework Statement:: The figure below shows a thin converging lens for which the radii are R1 = 8.48 cm and R2 = -11.4 cm. The lens is in front of a concave spherical mirror of radius R = 6.07 cm. If its focal points F1 and F2 are 4.58 cm from the vertex of the lens: b) If the lens and mirror are 20.3 cm apart and an object is placed 8.00 cm to the left of the lens, determine the position of the final image relative to the lens (Positive values are to the left).
Hi. There are a number of problems with the question.

The refractive index of the lens is missing. This makes it impossible to find the focal length of the lens.

A concave spherical mirror has only 1 focal point, so saying
“If its focal points F1 and F2 are 4.58 cm from the vertex of the lens”
makes no sense.

The question is incomplete. It looks like part a) has been omitted. It is often useful or necessary to see the whole question.

In your answer to b) ① you appear to be using the wrong value (4.58cm) for the focal length of the lens.

Edit. I'd already answered before I saw your post #2 saying you have solved the problem. But I would be very interested to know the resolution of the problems listed above!
 
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