Question

In the following diagram, the radius of curvature is and the object distance is .

• A. $-26cm$
• B. $-22cm$
• C. $+22cm$
• D. $+26cm$

Answer 1

Answer: (A), (B)

The correct options are
A $-26cm$
B $-22cm$

For any lens, whether it be concave or convex, the object is always taken on the left side of the lens, i.e. the object distance is measured to the left from the optic centre. Therefore, the object distance is always negative.
$⟹$ From the figure, the object distance = $-22cm$
A concave lens has a negative focal length, as the focus is always on the left side of the lens. So, the radius of curvature (= 2 $\times$ focal length) should also be negative.
$⟹$ From the figure, the radius of curvature = ${\text{OC}}_2$ = ${\text{OC}}_1$ = $-26cm$