Question
Question: A concave mirror gives an image 3 times as large as the object placed at a distance of 20 cm from it...
A concave mirror gives an image 3 times as large as the object placed at a distance of 20 cm from it. For image to be real, the focal length should be-
A
15 cm
B
10 cm
C
30 cm
D
20 cm
Answer
15 cm
Explanation
Solution
m = 
̃ – 3 = 
̃ – 3f – 60 = f
\ f = – 15 cm