Which one among the following is used to make periscope ?

A periscope is an optical instrument used for observation from a concealed position, such as in submarines, tanks, or bunkers [1][t2]. In its simplest form, a periscope consists of a tube with two plane mirrors fixed at each bend [t5]. These mirrors are placed parallel to each other and set at a 45-degree angle to the path of light [t1][t9]. The device operates on the laws of reflection; light from an object strikes the top mirror at 45 degrees and is reflected down the tube to the second mirror, which then reflects the light into the observer's eye [t5][t9]. While complex periscopes may use prisms or lenses for magnification and clarity, the fundamental component of a basic periscope is the plane mirror [t1][t2]. Concave mirrors and concave lenses are not used for the primary reflective mechanism in a standard periscope as they would distort the image [c2][c3].

Sources

1. [1] Science-Class VII . NCERT(Revised ed 2025) > Chapter 11: Light: Shadows and Reflections > 11.8.1 Periscope > p. 164