correct answer is (2) 6.67 cm
\({1\over v} + {1\over u}={1\over f}
\)
as radius of curvature is 10cm, focal length = \(f= \frac{R}{2}\)
thus, \(f=5 cm\)
u=-20cm.
thus \({1\over v}+{1\over -20}={1\over -5}\)
\({1\over v}=-\frac{3}{20}\)
v=-6.67cm
v= 6.67cm from pole
hence answer is (2) 6.67cm
