Reflection from Surfaces

Basics of Reflection

Reflection is the process where light bounces off a surface. When a ray of light hits a surface, it is called the incident ray. The ray that bounces off is the reflected ray. At the point where the light hits the surface, an imaginary line called the normal is drawn perpendicular (at 906) to the surface.

The key rule for reflection is:

Angle of incidence = Angle of reflection

These angles are measured between the ray and the normal. This means the angle at which light hits the surface is exactly the same as the angle at which it bounces away.

For instance, if a ray of light strikes a mirror at 306 to the normal, it will reflect away at 306 on the other side of the normal.

Types of Surfaces

The nature of the surface affects how light reflects:

• Smooth (plane) surfaces reflect light in a regular, predictable way called regular reflection. This produces clear images, like in a flat mirror.
• Rough surfaces cause light to scatter in many directions, known as diffuse reflection. This means no clear image is formed, but the surface is still visible because light is reflected in all directions.

For example, a polished mirror gives a clear reflection of your face, but a wall painted with matt paint reflects light diffusely, so you cannot see a clear image.

Ray Diagrams for Reflection

To draw ray diagrams for reflection:

• Draw the surface as a straight line.
• At the point where the light hits the surface, draw the normal as a dotted line perpendicular to the surface.
• Draw the incident ray approaching the surface at an angle to the normal.
• Draw the reflected ray leaving the surface at the same angle to the normal as the incident ray, but on the opposite side.

This method helps predict the direction of reflected rays and understand how images form in mirrors.

For example, if a ray hits a mirror at 406 to the normal, the reflected ray will leave at 406 on the other side of the normal.

Applications of Reflection

Reflection is used in many everyday devices:

• Mirrors: Flat mirrors produce virtual images that appear behind the mirror at the same distance as the object in front. The image is the same size and upright.
• Periscopes: Use two mirrors placed at 456 angles to reflect light down a tube, allowing people to see over or around obstacles.
• Everyday examples: Shiny surfaces like calm water or polished metal reflect light regularly, allowing us to see reflections. Rough surfaces like paper or cloth reflect light diffusely, so no clear image is seen.

In mirrors, the image formed is virtual because the reflected rays appear to come from behind the mirror but do not actually pass through that point.

For example, when you look in a bathroom mirror, your image appears behind the glass at the same distance you stand in front of it.

Further Explanation of Image Formation in Mirrors

The image in a plane mirror has these characteristics:

• Virtual: The image cannot be projected onto a screen because the light rays do not actually meet behind the mirror.
• Same size: The image is the same size as the object.
• Laterally inverted: The image is reversed from left to right (like a mirror image).
• Same distance: The image appears the same distance behind the mirror as the object is in front.

This is why your reflection in a mirror looks like you but reversed left to right.