Law of Reflection Virtual Demo Guide

Overview

When light hits a surface and changes its direction of propagation, this phenomenon is called reflection. It is because of reflection that we can see the glowing sun, as well as the non-luminous moon and everything around us. This experiment simulates an optical bench. By controlling the incident angle of a laser beam, we will summarize and verify the laws of reflection: 'three lines in one plane, two lines on opposite sides, and two angles equal'.

Background

• Ancient Greece: Euclid first proposed the law of reflection in 'Catoptrics', stating that the angle of incidence equals the angle of reflection.
• Islamic Golden Age: Alhazen further systematically studied the reflection and refraction of light, laying the experimental foundation for modern optics.
• Modern Era: Fermat proposed 'Fermat's Principle' (light travels the path that takes the least time), perfectly deriving the law of reflection from a theoretical height.

Key Concepts

Formulas & Derivation

Experiment Steps

1. 1

   Turn on Light Source

   Click the 'Laser Switch' to turn on the light source. You will see a red laser beam shooting towards the plane mirror at the bottom.
2. 2

   Change Angle of Incidence

   Drag the circular handle of the laser pointer. As you change the position of the incident ray, you will notice that the reflected ray also swings synchronously.
3. 3

   Observe Symmetry

   Check 'Show Angles' and 'Show Normal'. Observe whether the incident ray and the reflected ray are always symmetrical with respect to that dashed line (the normal).
4. 4

   Data Summary

   Change the angle multiple times, such as adjusting it to $30^\circ$, $45^\circ$, $60^\circ$. Record and compare the values on both sides to verify if $r$ is always equal to $i$.

Learning Outcomes

• Understand the reference role of the normal in optical experiments
• Confirm that the angle of reflection increases as the angle of incidence increases, and their values are always equal
• Clarify that the incident ray and the reflected ray lie on opposite sides of the normal
• Realize that when light shoots perpendicularly towards the mirror surface (angle of incidence is $0^\circ$), the reflected ray will return along the original path

Real-world Applications

• Mirrors: Utilizing the principle of image formation by plane mirrors to check one's appearance
• Bicycle Tail Lights: The inner wall is composed of small plane mirrors at right angles to each other, using multiple reflections to reflect light from car headlights back to the driver's eyes along the original path
• Periscopes: Using two parallel plane mirrors to change the path of light, enabling people underwater or in trenches to observe situations on the ground

Common Misconceptions

Further Reading

• Wikipedia - Reflection (Physics)