Question

Physics - Class X (Level-1)
22. An object of height 6 cm is placed on the principal
axis of a concave mirror of focal length fat a
distance of 4f. The length of the image will be
(1) 2 cm
(2) 12 cm
(3) 4 cm
(4) 1.2 cm​
please tell step by step explanation

Answer 1

It is a concave mirror so it is negative

Height of the object=6cm

Focal length =f=-f

Radius of curvature is =2*f (f)

=2f

Distance of the object =4f (u) =-4f

That means it is beyond the centre of curvature

Mirror formula:1/v+1/u =1/f

Sub in formula

1/v+-1/4f=-1/f

1/v=-1/f-1/4f

1/v=-4+1/4f

1/v=-3/4f

V=-4f/3

Height of the image = - (v/u) =hi/ho

-1/3=x/6

3x=-6

X=-2

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