# a concave mirror produces 3 times enlarged image of an object placed at 10 cm in front of it.Calculate radius of curvature of mirror

u= -10cm

m=+3= -v/u

=)v=30cm

1/f=1/v+1/u

=)1/f=u+v/uv

=)1/f = -10+30/-300

=20/-300

=)f= -15cm

R=2f= -30cm

• 65

Let the size of object be x cm.Then the size of image 3x
Given, object distance= u= -10 cm
(object distance is always negative for a real object)
focal length = f =?

Using, hi/ho =-v/u
3x/x = -v /-10
3     =v/10
3*10=v
v =30

Therefore the distance of image is 30 cm.

Now, v =30

Using, 1/v -1/u =1/f
1/f =1/v -1/u
=1/30 -1/10
= (1-3)/30
=-2/30
=-1/15
f = -15

Therefore the focal length of the concave mirror is 15cm.

Using, r = 2f
r = 2*-15
r = -30

Therefore the radius of curvature of the concave mirror is 30 cm

HOPE THIS HELPS!!!!!!!!!!!!!!!!!!

• 40

We know that :-

Magnification = -v/u

So, keeping values, we get :

+3 = -v/ -10

-30 cm = -v

30 cm = v

Now,using lens formula, we get :

1/v +1/u = 1/f

1/30 + (-1/10) = 1/f

1/30 - 1/10 = 1/f

1-3/30 = 1/f

-2/30 = 1/f

-1/15 = 1/f

-15 cm = f

Now, we know that :-

R = 2f

So,

R = 2(-15)

R = -30 cm

• 17
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