Question

The mirror used in periscope is:
A. Convex mirror.
B. Concave mirror.
C. Plane mirror.
D. Any of the above can be used.

Answer 1

Hint: Considering the rectilinear property of light, the periscope brings the image of an object to the observer above or below by reflecting it twice on mirrors. This is applied to view the outside surface from a submarine. For a voyage under water, it is practically impossible to swim up to the surface to check for some disturbance. From the principle of reflection this specific instrument came into picture and rescued the submarines.

Complete step by step answer:

When the object and the observer are at two different levels, the image of the object does not reach the eye of the observer as light can travel only in a straight line. The reflection from one mirror at an \[45{}^\circ \] inclination to the incoming object ray will direct the rays perpendicular to the incoming direction. The reflection from the second mirror at an \[45{}^\circ \] inclination will cause the required level shift to reach the observer. Plane mirrors serve well for this purpose and are covered by a perpendicular Z-shaped pipe. Plane mirrors reflect the exact shape and size of the object. The distance of the image is also the same as viewed from the reflection of plane mirrors. But for better viewing results, a complex structure of these mirrors are used to get the fine image. Hence all the mirrors along with lenses form the inside of the periscope. Therefore, the correct option is D.

Additional information:
Convex mirrors form an erect but magnified image and therefore cannot be used for naturally viewing purposes. The concave mirrors form real images and hence show inverted images of the object which will confuse the observer at different levels.

Note: For a simple periscope, only plane mirrors are used. For some distance visions, an enlarged view of the object is required and hence convex mirrors are helpful. A double inversion of the object will produce an erect image. This can be applied for convex mirrors to view too close objects.