The reflection of a light ray can be investigates using a ray box and a plane mirror.
The normal is the line drawn perpendicular to the mirror. The angle of incidence is the angle between the incident ray and the normal. The angle of reflection is between the reflected ray and the normal.
Measurements show that any light ray reflected by a mirror has the following properties:
i. the incident ray, the normal and the reflected ray to the surface all lie on the same plane, ii. angle of incidence = angle of reflection
These are the first and second laws of reflection respectively.
Types of reflection
There are two types of reflection: regular and diffused. In a regular reflection light is reflected in one direction, and it occurs on smooth surfaces. Diffused reflection occurs on rough surfaces and light is reflected through a range of different angles. However, both these types obey the rules of reflection.
Experiments
Law of reflection: to demonstrate the laws of reflection an apparatus can be set up using a ray box, protractor, strip of plane mirror and pieces of paper. The ray box is placed at an angle opposite the mirror at which the incidence ray is reflected. Vary the incidence ray and measure the angle of reflection.
Laws:
the incident ray, the normal and the reflected ray to the surface all lie on the same plane,
angle of incidence = angle of reflection
Position image formed by a plane mirror: to find the position and characteristics of an image formed by a plane mirror an experiment can be set up with the following apparatus: plane mirror, three pins, graph paper and a wooden holder. The graph paper is placed on
top of the soft board on top of which the plane mirror is placed held by the wooden holder. The pins are pinned into the board in front the mirror , from which an image is formed. Count the number of squares between the pins and the mirror, as well as between the images and the mirror to find the distances d1 and d2. Compare these distances.
The characteristics of an image formed by a plane mirror can be summarised as follows:
same size
laterally inverted
virtual
both the object and the image are equidistant from the plane mirror, d1 = d2
Plane mirrors are commonly used for optical testing, in periscopes, for blind corners and instrument scales.