How Does a Periscope Work? Law of Reflection Explained with Diagrams
Physics offers a powerful framework for understanding the natural world, using fundamental principles such as motion, energy, force, and the transfer of matter. One of the cornerstones in Physics, especially important for both academic understanding and practical applications, is the study of Optics and the foundational Laws of Reflection.
This topic supports learners as they visualize the behavior of light and comprehend its interactions with various objects—vital for fields ranging from engineering to medicine.
Fundamental Concepts and Laws in Physics
Physics breaks complex phenomena into manageable concepts governed by quantitative laws. For example, the Laws of Motion explore the relationship between forces and the movement of objects, while the Laws of Reflection describe how light behaves when it encounters surfaces.
Understanding these laws allows students to predict and analyze physical events, setting the stage for more advanced study in mechanics, electromagnetism, thermodynamics, and modern Physics.
Detailed Explanation and Example: Law of Reflection
The Law of Reflection states that when a light ray strikes a smooth surface, the angle at which it hits the surface (angle of incidence) is equal to the angle at which it bounces off (angle of reflection).
This law is a key principle for understanding image formation in mirrors and devices like periscopes. It forms the base for problem-solving in optics.
Formula:
Angle of Incidence (i) = Angle of Reflection (r)
Example:
If a light ray hits a plane mirror at an incidence angle of 30°, it reflects off the surface at an angle of 30° on the opposite side of the normal. This simple rule allows you to construct ray diagrams for mirrors, periscopes, and other optical instruments.
Step-by-Step Problem-Solving Approach
- Read and analyze the problem carefully. Identify known and unknown variables.
- Draw a neat and labeled diagram representing the physical setup.
- Apply the appropriate laws or formulas, such as Newton’s laws or the law of reflection.
- Set up equations based on the diagram and substitute known values.
- Solve stepwise, ensuring all physical quantities have correct units.
- Review the solution for accuracy and physical feasibility.
Key Physics Formulas and Their Applications
| Concept | Formula | Application |
|---|---|---|
| Law of Motion | F = m × a | Calculates force required for given mass and acceleration |
| Work Done | W = F × d × cosθ | Measures mechanical work when force acts over distance |
| Law of Reflection (Optics) | i = r | Predicts angle of reflected light in mirrors |
| Ohm’s Law (Electricity) | V = I × R | Relates voltage, current, and resistance in circuits |
Applications: Real-World Usage of Physics Concepts
- Mirrors and periscopes apply the law of reflection to enable indirect viewing of objects.
- The laws of motion guide automotive and aerospace engineering designs.
- Ohm’s law and electromagnetic principles are fundamental in designing electrical circuits and devices.
- Thermodynamics governs engine efficiency, refrigeration, and environmental controls.
Practice Question Example
Practice:
A light ray strikes a plane mirror at an angle of 40° to the normal. What is the angle between the incident and reflected ray?
Solution:
The angle of incidence = angle of reflection = 40°.
Total angle between the rays = angle of incidence + angle of reflection = 40° + 40° = 80°.
Summary Table: Physics Problem-Solving Steps
| Step | Action | Purpose |
|---|---|---|
| 1 | Read and identify variables | Clarifies what is given and required |
| 2 | Draw diagram | Provides visual aid |
| 3 | Select formula/law | Ensures correct approach |
| 4 | Substitute values & solve | Obtains quantitative answer |
| 5 | Double-check units & logic | Confirms accuracy |
Relevant Vedantu Resources and Practice
Next Steps for Deeper Learning
- Practice drawing ray diagrams for mirrors, periscopes, and lenses.
- Attempt numerical questions on work, energy, and circuits.
- Explore real-life applications of core physics laws in engineering and technology fields.
FAQs on Periscope: Working Principle, Construction, and Applications
1. What is a periscope and how does it work?
A periscope is an optical instrument that allows you to see over, around, or through obstacles by using two plane mirrors placed parallel at 45° angles. It works on the law of reflection as each mirror reflects light down the length of the tube, redirecting the image to the viewer’s eye. The process involves:
- Light from the object strikes the upper mirror.
- The light reflects down the tube to the lower mirror.
- The lower mirror directs the light to the viewer’s eye, allowing observation from a concealed or low position.
2. What is the principle behind a periscope?
The working principle of a periscope is the law of reflection. According to this law, the angle of incidence equals the angle of reflection. In a periscope, two plane mirrors are set at 45°; light rays entering the periscope reflect off both mirrors and travel to the observer’s eye, enabling indirect viewing.
3. What materials are used to construct a simple periscope?
A simple periscope is usually made of:
- Two plane mirrors, typically glass with a reflective coating.
- A rectangular cardboard or plastic tube to form the body.
- Support materials like tape or glue to hold the mirrors at the correct angles.
4. Can you draw and explain the ray diagram of a periscope?
In a periscope ray diagram, incoming light from an object strikes the top mirror at a 45° angle, reflects vertically down the tube to the bottom mirror (also at 45°), and then reflects to exit horizontally to the viewer’s eye. Each reflection maintains equal angles of incidence and reflection, as per the law of reflection, allowing the image to reach the observer. Diagrams should clearly show both mirrors at 45° and the path of the light rays.
5. What are the main uses of periscope in daily life and industry?
Periscopes are useful for observing areas that are out of direct sight. Main uses include:
- Submarines: To observe above water while remaining submerged.
- Military trenches: For safe observation over barriers.
- Tanks and armored vehicles: For vision without exposure.
- Amusement parks and process monitoring: To see over crowds or enclosed machinery.
6. What is the difference between a periscope and a telescope?
The main differences between a periscope and a telescope are:
- Periscope: Uses two plane mirrors to reflect light and allow viewing around barriers; works by reflection.
- Telescope: Uses lenses and/or curved mirrors to magnify distant objects; works mainly by refraction (and sometimes reflection in reflecting telescopes).
7. Why are the mirrors in a periscope kept at 45° angles?
The mirrors are set at 45° angles so that light from the external object can be reflected downward (or upward) twice, allowing the image to travel the length of the periscope. This ensures the light emerges at a right angle into the viewer’s eye, maintaining the original orientation of the viewed scene.
8. What type of image is formed in a periscope?
A periscope forms a virtual, erect, and laterally inverted image of the object due to the use of plane mirrors. The image appears the same size and orientation as the original object, except for lateral inversion.
9. Who invented the periscope and what is its history?
The invention of the periscope is attributed to Simon Lake (for submarines) and Sir Howard Grubb (for military purposes) in the late 19th and early 20th centuries. Earlier, similar devices were used by hippolyte Marié-Davy and others during the mid-19th century. Periscopes became essential in wartime observation and submarine navigation.
10. What common misconceptions do students have about periscopes?
Common misconceptions include:
- Thinking periscopes use lenses (they primarily use plane mirrors in basic designs).
- Believing periscopes magnify images (simple periscopes do not).
- Assuming the image is real and not virtual (periscopes form a virtual image).
11. How is the law of reflection applied in a periscope?
The law of reflection states that the angle of incidence equals the angle of reflection. In a periscope, both mirrors are set at 45°, so light reflects twice at equal angles, redirecting the image from the object to the viewer's eye without changing its size or orientation (other than lateral inversion).
12. How can students make a DIY periscope for a school project?
To make a simple periscope for a project:
- Get a rectangular cardboard tube.
- Cut two slots at 45° angles near each end of the tube.
- Insert two plane mirrors into the slots, facing each other diagonally.
- Secure the mirrors firmly with tape or glue.
- Look through the lower opening to observe images above or around obstacles, demonstrating the law of reflection in action.
