Question

If AB = 10 cm & DB = 40 cm (diameter). What is the radius of curvature & focal length of the spherical glass?

• 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

Given:
Diameter of the sphere = DB = 40 cm.
Radius of curvature (DO or OB) is half of diameter of curvature (DB) = 20 cm.
Focus is at point A since parallel rays after reflection pass through point A.
Focal length (f) is half of the radius of curvature (R)
$\therefore f=\frac{R}{2}$
$=\frac{20}{2}=10cm$