Diamond Ring in Front of a Convex Lens?

[itsgood819]

Homework Statement

A 1.5 cm high diamond ring is placed 20 cm in front of a convex lens whose radius of curvature is 30 cm.

a) What is the position and the size of the image?
b) What magnification does this lens have?

Homework Equations

1/f= 1/d_i + 1/d_o
m= -d_i/d_o or h_i/h_o

The Attempt at a Solution

the 20 cm is d_o, and the h_o is 1.5 cm. Since it's a lens, I don't know the focal length. I tried using the 1/f= 1/d_i + 1/d_o, but I don't any variable besides the d_o.

How would I solve this problem? Help please, and thank you! Also, I'm new to this forum so my posting might look a bit weird.

 

[Doc Al]

Is it a double convex lens with both sides having the same radius of curvature? If so, you can use the lens maker's formula to figure out the focal length.

 

[wbandersonjr]

Because, the index of refraction of the lens material is not given, I would assume that f=R/2.

 

[itsgood819]

thank you for your suggestions! it turns out that my teacher actually meant to put mirror instead of lens.

 

[Doc Al]

it turns out that my teacher actually meant to put mirror instead of lens.

Aha! Now the problem makes sense.