Reflection of light — KCSE Physics

The laws of reflection are fundamental principles governing how light behaves when it strikes a reflective surface. There are two main laws:

1. The angle of incidence equals the angle of reflection: This means that the angle at which light hits a surface (angle of incidence) is equal to the angle at which it bounces off (angle of reflection).
2. The incident ray, reflected ray, and normal lie in the same plane: This indicates that these three elements are always on the same flat surface.

To illustrate these laws using a ray diagram for a plane mirror:

• Draw the mirror as a straight vertical line.
• Identify the normal line perpendicular to the mirror surface at the point of incidence.
• Mark the angle of incidence (i) from the incident ray to the normal.
• Draw the reflected ray at the same angle (r) to the normal on the opposite side.

This visualization helps in understanding how images are formed in plane mirrors, where the image distance equals the object distance.

In this lesson, we will describe the properties of images formed by plane mirrors. When light reflects off a plane mirror, it creates an image with the following characteristics:

• Virtual: The image cannot be projected on a screen as it appears to be behind the mirror.
• Upright: The image maintains the same orientation as the object, meaning it is not inverted.
• Same size: The dimensions of the image are identical to those of the object.
• Laterally inverted: The image is reversed from left to right, so the right side of the object appears on the left side of the image.

For example, if you stand in front of a plane mirror, your reflection will appear upright, the same size as you, and will be reversed in terms of left and right.

To summarize:

• Plane mirrors produce virtual images.
• Images are upright and the same size as the object.
• Images are laterally inverted, reversing left and right.

Plane mirrors are crucial in various optical devices due to their ability to reflect light and form images. Here are some key uses:

• Periscopes: Used in submarines to allow viewing from below water. They consist of two plane mirrors arranged at 45-degree angles, enabling light to reflect and provide a view above the water's surface.
• Kaleidoscopes: These devices create beautiful patterns through multiple reflections. They use plane mirrors positioned at angles to reflect light, producing symmetrical designs as objects inside are rotated.
• Rear-view mirrors: Commonly found in vehicles, these mirrors provide drivers with a view of the area behind them. They are typically slightly curved to widen the field of view and reduce blind spots.

In all these applications, the plane mirror's ability to produce clear and upright images is essential for functionality.