What is a Periscope?

S4-SA1-0340

Grade Level:

Class 7

Space Technology, EVs, Climate Change, Biotechnology, HealthTech, Robotics, Chemistry, Physics

Definition

What is it?

A periscope is an optical instrument that uses mirrors or prisms to allow you to see objects that are not in your direct line of sight. It helps you see around corners, over obstacles, or from a hidden position, like from inside a submarine.

Simple Example

Quick Example

Imagine you are standing behind a tall wall at a cricket ground and can't see the match. If you had a simple periscope, you could hold it up, and the mirrors inside would let you see the scoreboard or the batsman without having to peek over the wall yourself.

Worked Example

Step-by-Step

Let's build a simple periscope with two mirrors:
1. Take a long cardboard box or tube.
2. Cut two slots, one near the top and one near the bottom, on opposite sides of the tube.
3. Angle the top mirror at 45 degrees, facing downwards, so it catches light from the object you want to see.
4. Securely fix this mirror inside the top slot.
5. Angle the bottom mirror at 45 degrees, facing upwards, so it catches the light reflected from the first mirror.
6. Securely fix this mirror inside the bottom slot.
7. Look into the bottom mirror. The light from the object will hit the top mirror, reflect down to the bottom mirror, and then reflect into your eye.
8. You can now see the object over the obstacle! This is how a periscope works.

Why It Matters

Periscopes are crucial in fields like defence, allowing submarines to see above water without surfacing. They also inspire technologies in robotics for remote viewing and in space technology for observing distant objects. Understanding periscopes can open doors to careers in engineering, defence, and optics.

Common Mistakes

MISTAKE: Thinking a periscope magnifies objects. | CORRECTION: A simple periscope only changes the direction of light, allowing you to see objects indirectly; it does not make them appear larger or closer.

MISTAKE: Believing periscopes use lenses for basic vision. | CORRECTION: Simple periscopes primarily use flat mirrors to reflect light. While advanced periscopes might use lenses for magnification, the core principle relies on reflection.

MISTAKE: Assuming both mirrors in a periscope face the same direction. | CORRECTION: The mirrors must be angled at 45 degrees to the tube's length and face each other (one down, one up) to reflect light effectively from the object to the observer's eye.

Practice Questions

Try It Yourself

QUESTION: What is the main purpose of a periscope? | ANSWER: To see objects that are not in your direct line of sight, typically over or around obstacles.

QUESTION: If the top mirror in a periscope is removed, what would happen when you try to look through it? | ANSWER: You would not be able to see anything because the light from the object would not be reflected downwards to the second mirror.

QUESTION: A submarine uses a periscope to observe a ship on the surface. If the periscope is 10 meters long and its mirrors are perfectly clean, how far away can the submarine 'see' the ship (assuming no other visual limitations)? | ANSWER: The length of the periscope (10 meters) does not limit the distance it can see; it only determines how high above the submarine it can extend. A periscope can see as far as the line of sight allows, limited by the Earth's curvature and atmospheric conditions, not its own length.

MCQ

Quick Quiz

Which optical component is essential for a simple periscope to work?

Lenses

Prisms

Flat mirrors

Fibre optics

The Correct Answer Is:

A simple periscope works by reflecting light using two flat mirrors. Lenses are used for magnification, prisms are for advanced light bending, and fibre optics transmit light, but mirrors are key for basic periscope function.

Real World Connection

In the Real World

In India, periscopes are vital for our Navy's submarines, allowing them to navigate and observe without revealing their position. Beyond defence, periscope-like optical systems are used in industrial inspection, letting engineers view hard-to-reach parts of machinery, or even in some advanced endoscopes used in medical procedures.

Key Vocabulary

Key Terms

OPTICAL INSTRUMENT: A device that helps us see or analyse light, like a telescope or microscope. | REFLECTION: The bouncing back of light when it hits a surface. | LINE OF SIGHT: The imaginary straight line along which an observer has an unobstructed view. | SUBMARINE: A watercraft capable of independent operation underwater. | MIRROR: A surface, typically glass coated with a metallic amalgam, that reflects a clear image.

What's Next

What to Learn Next

Next, explore 'Reflection of Light' in more detail! Understanding how light bounces off surfaces is the core principle behind periscopes and will help you grasp other cool optical devices like telescopes and cameras. Keep learning!