1. What reflection really means
Reflection is the simple idea that when light hits a surface, a part of it bounces back into the same medium. This is why we can see ourselves in mirrors and why shiny objects appear bright.
To understand reflection properly, I usually imagine a single thin ray of light falling on a smooth surface and think about how it returns along a predictable path.
2. Basic terms I need to know
Whenever I draw a reflection diagram, I use these standard terms:
- Incident ray: The ray of light coming towards the surface.
- Point of incidence: The exact point where the incident ray hits the surface.
- Normal: An imaginary line drawn perpendicular to the surface at the point of incidence.
- Reflected ray: The ray of light that bounces back from the surface.
- Angle of incidence (i): The angle between the incident ray and the normal.
- Angle of reflection (r): The angle between the reflected ray and the normal.
These angles are always measured from the normal, not from the surface.
3. Laws of reflection
Reflection follows two fixed laws. I keep these in mind whenever I draw any ray diagram:
3.1. 1) The incident ray, normal and reflected ray lie in the same plane
All three lines — incident ray, normal and reflected ray — lie on a single flat plane. This tells me that the reflected ray cannot suddenly jump out of the diagram; it must stay in the same geometric plane.
3.2. 2) Angle of reflection equals angle of incidence
This is the most important rule:
\( i = r \)
No matter how the ray strikes the surface, as long as it is a smooth reflecting surface, the angle with which light comes in equals the angle with which it goes out.
4. Regular and irregular reflection
Depending on the smoothness of the surface, reflection can appear in two forms:
4.1. Regular (specular) reflection
This happens on smooth surfaces like a mirror. All reflected rays are parallel and form a clear image.
4.2. Irregular (diffuse) reflection
This happens on rough surfaces. Each small part of the surface reflects at a slightly different angle, so the rays scatter in different directions. No clear image is formed, but we can still see the object because light reaches our eyes.
5. Why the laws make sense
To me, the laws of reflection feel natural when I think of light as a stream of tiny packets hitting a surface. The surface pushes them away symmetrically, so the incoming and outgoing angles match.
Another way to see this is through geometry: a smooth surface acts like a perfectly straight boundary, and straight-line geometry forces the angles to obey the \(i = r\) rule.
6. Simple example to understand reflection
Imagine a ray of light striking a smooth surface at an angle of \(30^\circ\) with the normal:
- The angle of incidence is \( i = 30^\circ \).
- By the law of reflection, the reflected ray must leave at \( r = 30^\circ \).
Even if I draw the diagram roughly, the symmetry becomes visible — the two angles are always equal.
7. Some everyday places where I notice reflection
Reflection appears in many simple situations around me:
- Seeing myself in a mirror.
- The shine on polished floors.
- Bright spots of light on water surfaces.
- Periscopes and simple optical devices.
Even when a surface is not perfectly smooth, it still reflects light — just not in a neat, image-forming way.