Question

viii) A concave mirror having radius of curvature 20 cm has a focal length
a) +10 cm
b) +40 cm
c) -10 cm
d) -40 cm
​

Answer 1

Answer:

f = 2 r

f = 2 * 20

f = 40 cm

option b) +40 is correct

Answer 2

R=2f
Then, 20=2f
f=20/2=10cm

a) +10cm is correct