Correct Option
The correct option is (c) 1 and 3 only.
Explanation
A periscope is an optical instrument used to observe objects from a concealed position or when the direct line of sight is obstructed. It operates based on the laws of reflection using plane mirrors or prisms.
Statement-wise Analysis
- Statement 1 is Correct: The working of a periscope relies on the principle of multiple reflections. Light from an object strikes the first mirror, is reflected through the tube, strikes the second mirror, and is reflected again to reach the observer's eye.
- Statement 2 is Incorrect: In a simple periscope, the two plane mirrors are arranged parallel to each other, not at right angles. Each mirror is fixed at an angle of 45° to the axis of the tube. This specific arrangement ensures that light turns 90° at the first mirror and another 90° at the second mirror, allowing the final emergent ray to be parallel to the incident ray. If the mirrors were at right angles to each other, the light would be reflected back toward the source (retro-reflection).
- Statement 3 is Correct: The primary function of a periscope is to enable the viewing of objects situated above, below, or around an obstacle (such as a wall, trench, or water surface) that prevents direct line-of-sight observation. It is widely used in submarines and military bunkers.
Key Takeaway: A simple periscope utilizes two plane mirrors placed parallel to each other and inclined at 45° to the optical path to view obstructed objects through successive reflections.