Applied Optics: Which instrument allows a submerged submarine to view objects at or just above the water's surface? Used for observation while remaining below the surface. Choose the correct instrument.

What is being asked?
The name of the optical device that lets a submarine observe the surface while staying submerged.

Given data

• Environment: Underwater (submarine)
• Task: Look at/near the water surface

Concept/Approach
A periscope uses a system of mirrors/prisms at 45° (or total internal reflection prisms) to relay the line of sight from above the surface down to the viewer.

Step-by-step reasoning
1) Requirement: Maintain stealth while observing → instrument must elevate sightline.2) Periscope meets this by folding the optical path; other devices (kaleidoscope/spectroscope/telescope) do not provide the necessary geometry.

Common pitfalls
Mistaking telescope (magnification) for periscope (geometry for hidden viewing).

Final Answer
Periscope