An equiconvex lens of glass (refractive index ) has both radii of curvature equal to . It is completely immersed in a liquid of refractive index . What is its focal length in the liquid?
Answer and explanation
Correct answer: D. 56.0 cm
- Step 1: According to the lens-maker's equation for a lens immersed in a surrounding medium, .
- Step 2: For an equiconvex lens with and , the geometric factor is .
- Step 3: Substitute relative refractive index : .
- Step 4: Inverting yields a focal length of in the liquid.
Answer
56.0 cm.
Why not the others: 13.3 cm is the focal length of the lens in air; 40.0 cm fails to divide the relative index by the liquid index (); 112.0 cm accounts for only a single refracting surface.
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