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