Question

For an object at infinity, a concave mirror produces an image at its focus which is:
$\left( a \right)$ Enlarged, inverted and virtual
$\left( b \right)$ Virtual
$\left( c \right)$ Erect
$\left( d \right)$ Real, inverted and diminished

Answer 1

Hint – In this question use the concept that the position of center of curvature in case of a concave mirror lies in front of the mirror and the focal length is also positive, that is focus lies in front of mirror. This will help commenting upon the image formed by a concave mirror for an object placed at infinity.

Step-By-Step answer:

The difference between concave and convex mirror is as follows:

S/N	Differentiating property	Convex mirror	Concave mirror
1	Mirror shape	Convex mirror rounded or curved like the exterior of a circle or sphere.Also called a fish eye or diverging mirror.Convex mirror is curved outside.	Concave mirror is rounded or hollowed like the interior of a circle or a sphere.Also called a converging mirror.Concave mirror is curved inside.
2	Position of focus	Focus lies behind the mirror i.e. focal length is negative.	Focus lies in front of the mirror i.e. focal length is positive.
3	Position of center of curvature	Behind the mirror.	In front of the mirror.
4	Position of the object which is at infinity	At the focus and behind the mirror.	At the focus in front of the mirror.
5	Size of object when it is placed at infinity.	Highly diminished as compared to that of the object.	Much diminished as compared to that of the object.
6	Image of the object when it is placed at infinity.	Image is virtual and erect.	Image is real and inverted.

So when the object is placed at infinity in case of a concave mirror image is formed at the focus which is real, inverted and diminished.
So this is the required answer.
Hence option (D) is the correct answer.

Note – The main difference between a real image and a virtual image is that a real image will always be formed by a converging mirror, however a virtual image will be formed by a diverging mirror. Inverted image is the key word used for a reversed image if the image is upside down with respect to the object then it is termed as inverted. Diminished means that the size of the image is altered as the formed image is small in comparison to the actual size of the object.