Understanding the Simple Periscope's Working Principle

A simple periscope is an optical instrument used to see objects that are otherwise obstructed, such as over a wall or around a corner. It works by using mirrors or prisms to change the direction of light from the object to the observer's eye. The question asks about the fundamental natural phenomenon behind the operation of a simple periscope.

Components of a Simple Periscope

A simple periscope typically consists of:

• A tube (often a long one).
• Two plane mirrors placed parallel to each other inside the tube.
• The mirrors are angled at 45 degrees with respect to the axis of the tube. One mirror is at the top end, and the other is at the bottom end.

How Light Travels in a Simple Periscope

Let's trace the path of light from an object being viewed through a simple periscope:

1. Light rays from the object travel horizontally towards the top mirror of the periscope.
2. When the light rays strike the top mirror (placed at a 45-degree angle), they bounce off its surface and travel vertically down the tube. This bouncing of light is called reflection.
3. The light rays then reach the bottom mirror, which is also placed at a 45-degree angle at the bottom end of the tube.
4. When the light rays strike the bottom mirror, they bounce off its surface again, travelling horizontally towards the observer's eye. This is another instance of reflection.
5. The observer sees the image of the object.

The entire process relies on the light rays changing direction by bouncing off the polished surfaces of the mirrors.

Analyzing the Options and the Key Phenomenon

Let's consider the given natural phenomena:

• Reflection of light: This is the phenomenon where light bounces off a surface. Mirrors are specifically designed to cause reflection. As described above, light bounces off both mirrors in the periscope.
• Refraction of light: This is the bending of light as it passes from one medium to another (e.g., from air to glass). A simple periscope with plane mirrors does not primarily use refraction.
• Dispersion of light: This is the splitting of white light into its constituent colours, as seen with a prism or a rainbow. This phenomenon is not involved in the basic working of a simple periscope.
• Total internal reflection of light: This occurs when light travels from a denser medium to a less dense medium and strikes the boundary at an angle greater than the critical angle, causing all the light to reflect back into the denser medium. While some advanced periscopes might use prisms employing total internal reflection, a simple periscope with plane mirrors works based on regular reflection.

Based on the path of light through the simple periscope, the fundamental principle at play is the bouncing of light rays off the mirrors, which is the definition of reflection of light.

Conclusion: The Simple Periscope and Reflection

A simple periscope operates by employing two instances of reflection of light using plane mirrors. Light from the object undergoes reflection at the top mirror and then again at the bottom mirror before reaching the observer's eye. Therefore, the natural phenomenon based on which a simple periscope works is reflection of light.

Revision Table: Key Optics Concepts for Periscopes

Additional Information: Beyond Simple Periscopes

While simple periscopes use plane mirrors and rely purely on reflection of light, more complex periscopes, especially those used in submarines or tanks, often use prisms instead of mirrors. These prisms are designed to achieve the same redirection of light but can be more durable and provide better image quality. Prisms in such periscopes often utilize the phenomenon of total internal reflection, which is a specific type of reflection occurring within the prism material.

However, the question specifically asks about a "simple periscope," which is conventionally understood to use plane mirrors and thus rely on basic reflection of light.