Question

An object is lest at 20 cm from the pole of a concave mirror it from real image at a distance of 60 cm from the pole find focal length of concave mirror

Answer 1

Answer:-15

Explanation:

given,

Focal length(f)=?

Object distance(u)= -20cm

Image distance(v)= -60cm

We know

1/f = 1/v+1/u

Now, putting values

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

Taking L.C.M.

1/f= -1-3/60

1/f= -4/60

1/f= -1/15

f= -15cm

Therefore, f= -15cm.

Thus the focal length should be -15cm .

Answer 2

The distance between the pole P of the concave mirror and the focus F is the focal length of the concave mirror. Thus, the focal length of a concave mirror can be estimated by obtaining a 'Real image' of a distant object at its focus, as shown in the figure.