Question

A concave mirror gives an image three times as large as
the object placed at a distance of 20cm from it. For the
image to be real, the focal length should be
(a) 10cm ) 15cm (c) 20cm (d) 30cm
​

Answer 1

Answer:

focal length=-15(b)

Explanation:

Magnification=3

-v/u=3

u=-20

v=-60

1/v+1/u=1/f

i/-60+1/-20=1/f

-1/60-1/20=1/f

-4/60=1/f

f=-15 cm