Question

A boy is standing in front of two big mirrors P and Q fitted side by side on a wall. He can see the erect image of his face in both the mirrors, the size of his face in mirror P remains the same but it goes on increasing in mirror Q. Which one of the following is correct?

A) Mirror P is convex and Q is concave

B) Mirror P is plane and Q is concave

C) Mirror P is plane and Q is convex

D) Mirror P is concave and Q is plane

Answer 1

Here, when the boy standing in front of the mirror he sees erect images in both.
Erect images are formed by convex and plane mirrors. Concave mirrors erect images only when we place the object between pole and focus. And only concave mirrors magnify the object size.

Formula used:
$R = \dfrac{{\rho L}}{A}$

Complete step by step answer:
A plane mirror forms upright and virtual images. Size of the image is the same as the object size and distance of the image is the same as the object distance. For a plane mirror, the distance of the image from us will be twice the real distance. A plane mirror doesn’t have a focal point. Hence, after reflection the light rays will take the same straight line path, but in the opposite direction. When we extend this reflected ray to locate an image, it will go straight behind the mirror also and in turn it results in the same size of image and same distance. Thus, for all real objects, a plane mirror produces only virtual images, which are erect and have the same size as the object.
Image formation in a concave mirror is different from a plane mirror. In a concave mirror it mainly depends on the distance between the mirror and the object. Concave mirrors form real and virtual images. When an object is placed in front of the concave mirror, a virtual and magnified image is obtained. If we increase the distance between the mirror and the object, the size of the image reduces and real images are formed. And if we decrease the distance between the mirror and the object, the image size increases. The focal point and the centre of curvature lie in front of the concave mirror.
When the object is placed far from the concave mirror, an inverted image is formed at the focal point. The image formed is real, as the light rays focus at the image location. As the object moves towards the mirror the image location moves further away from the mirror and size of the image increases and the images are inverted. When the object is at the focal point of the mirror, the image is at infinity. As we move the object closer to the mirror, a virtual and upright image forms inside the focal point behind the mirror. Initially the virtual image is larger than the object and far from the mirror, but as the object approaches the mirror the virtual image also approaches the mirror and size of the image is decreased.
Answer is option B.

Note:
A convex mirror cannot form magnified images. It converges the rays and produces smaller images. But a magnified image is formed only when the object is virtual and the image is real which is not possible for normal setup.