Question

When the object is at infinity from a concave mirror, the image formed is
A) at the focus
B) virtual and erect
C) highly enlarged
D) None of these

Answer 1

Hint: Concave mirror is the spherical mirror which is used to produce the magnified image of an object. Concave mirrors produce both real and virtual images. When the object is behind the mirror, it produces the virtual images.

Complete step by step answer:
(i) Based on the position of an object, we can say the nature of the image. In concave mirror images formed when the object is at infinity, beyond the center of curvature, at the center of curvature, between the focus and the center of curvature, at the focus, between the pole and focus.
(ii) When the object is at infinity, the incident rays are parallel to the principal axis. Hence the image is formed at the focus. And the image is real and inverted but in diminished size.

Hence we can say that the image formed at the focus. Therefore, the correct option is option A.

Additional information:
(i) Concave mirror is the only mirror to produce both real and virtual images with a magnified size.
(ii) Let’s see the cases happening in the concave mirror. They are
Case 1: When the object is at infinity,
- The incident rays are parallel to the principal axis
- Image is formed at the focus
- Image form is real, inverted, and diminished in size.
Case 2: When the object is beyond the center of curvature
- Incident rays are parallel to the principal axis
- Image is formed between the center of curvature and the focus
- Image formed is real and inverted and diminished than the object.
Case 3: When the object is at the center of curvature
- Image is formed at the center of curvature
- Image formed is real and inverted and the same size as an object.
Case 4: When the object is between the center of curvature and the focus
- Image is formed beyond the center of curvature
- Image formed is real and inverted and magnified
Case 5: Object is at the focus:
- Image formed at the infinity
- Image formed is real and inverted and highly magnified
Case 6: The object is between the pole and focus
- Image is formed behind the mirror
-Image formed is virtual and erect and magnified

Note:
If the object is at the infinity, the image is formed at the focus. If the object is at the focus, the image is formed at the infinity. And the spherical mirrors produce virtual images only when the image is formed behind the mirror. In the given case, the concave mirror produces only the diminished image as the object is at infinity.