Question

An object of length $4cm$ is placed in front of a concave mirror at a distance of $30cm$. The focal length of mirror is $15cm$. What will be the length of image?

• A. $1cm$
• B. $2cm$
• C. $4cm$
• D. $6cm$

Answer 1

The correct option is C $4cm$

The relationship between the radius of curvature and focal length is that the radius of curvature is twice the focal length.

In this case, focal length of the concave mirror is given as $15cm$. Hence, the radius of curvature is $15\times 2=30cm$.

When the object is placed on the centre of curvature, on the principal axis, in front of a concave lens, the image is formed at the same point. The image formed is real and inverted.

So, in this case, the object distance is equal to the image distance.

Therefore, the object size is equal to the image size.

As the object is of $4cm$ in length, the image will also be of $4cm$ in length.