Question

When an object is 30cm from a concave mirror, the object and image are of same height. What is the focal length of the mirror

Answer 1

Answer:

Given,

Focal length, f=−30 cm if u=−x

real ⇒ same side ⇒v=−ve

Magnification, m=

u

v

⇒v=m×u=3×(−x)=−3x

From mirror formula,

f

1

=

v

1

+

u

1

We get

−30

1

=

−3x

1

+

−x

1

⇒

30

1

=

3x

1+3

⇒

4

3x

=3⇒x=40 cm

So object should be placed at 40 cm to the mirror.

Explanation:

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