The correct option is (c).
Explanation
A periscope is an optical instrument that allows an observer to view objects that are not in the direct line of sight. It is typically used to look over, around, or through obstacles, utilizing the laws of reflection.
Statement-wise Analysis
- Statement 1 is Incorrect. Periscopes are primarily used in submarines to view the surface while submerged, and in land warfare (tanks and bunkers) to observe surroundings without exposure. They are not primarily used in aircraft for navigation; aircraft rely on avionics, radar, and direct visual contact.
- Statement 2 is Correct. In military applications, specifically in trench warfare or bunkers, periscopes allow soldiers to observe the battlefield and enemy movements while remaining safely concealed behind armor or earthworks.
- Statement 3 is Correct. A simple periscope consists of a tube with two plane mirrors (or right-angled prisms) located at each end. These mirrors are inclined at an angle of 45° to the axis of the tube and are parallel to each other. This arrangement reflects light from the object down the tube and then to the observer's eye.
Key Takeaway: A periscope functions based on the principle of multiple reflections of light. In its simplest form, it employs two plane mirrors placed parallel to each other at a 45° angle to change the path of light rays.