Question

If AO= 10 cm & BO = 40 cm (diameter). What is the radius of curvature & focal length?

• A. 40 cm, 10 cm
• B. 20 cm, 20 cm
• C. 40 cm, 5 cm
• D. 20 cm, 10 cm

Answer 1

The correct option is D

20 cm, 10 cm

Here $C$ is the centre of sphere.
Radius of curvature $R$ = 20 cm. Focus is point A since parallel rays pass through point A. So, AO = focal length = $\frac{R}{2}=10cm$