Question

An object is placed at distance of 25 cm from a spherical mirror and its image is formed behind the mirror at distance of 5 cm. Find focal length? Is it concave or convex mirror?

Answer 1

Explanation: u = -25 cm , v = 5 cm from the mirror formula 1/f =1/u + 1/v  

Then 1/f = -1/25 + 1/5 = 4/ 25  

F = 6.25 cm  

As the focal length is positive the mirror is convex in nature.  

Answer 2

Answer:

Focal length is 6.25cm and the mirror is convex in nature.

Explanation:

From the question we can say that,

The object distance, which is u, = 25cm.

We know that object distance is always negative.

Therefore, u = -25cm

Also, we know that image distance, v = 5cm.

Now we apply the mirror formula,

=) 1/f = 1/v + 1/u

=) 1/f = 1/5 + 1/-25

=) 1/f = 1/5 - 1/25

=) 1/f = 4/25

=) f = 6.25cm.

Now, we know that if the focal length is positive the mirror will be convex.

Hence, it is a convex mirror.

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