Question

A concave mirror produces the image same as the size of object find object distance image distance when the focal length is 2cm.​

Answer 1

Answer:

Correct option is

C

n

(n+1)

f

Let the object be placed at a distance x from the mirror.

Object distance, u=−x

Image distance, v

Focal length, f

Magnification: m=−

u

v

=−n

⟹v=nu=−nx

Applying mirror formula:

f

1

=

v

1

+

u

1

Substituing the values

For a concave lens f is negative

−

f

1

=−

nx

1

−

x

1

⇒

f

1

=

x

1

(1+

n

1

)

⇒

f

1

=

x

1

(

n

n+1

)

⇒x=

n

(n+1)

f

Answer 2

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Here h¹ = 2cm, u = -16cm,h² = -3cm (Since image is real and inverted)

→m = h²/h¹ = -v/u

→v = -h²/h¹ u = 3/2 × (-16) = -24cm

1/f = 1/v + 1/u = -1/24 -1/16 = -2-3/48 = -5/48;f = -48/5 = -9.6cm