Reflection of light
When a ray of light is incident on a luminous plane moving in a medium,most of its energy strikes that plane and returns back to the same medium in the form of ray.This phenomenon is called reflection of light. Reflection of light is an example of light falling on a mirror and returning back to the same medium.This type of reflection is also called regular reflection.
The plane through which the light strikes and reflects is called the reflecting plane. The ray falling on the plane is called the incident ray while the ray returning back to the same medium after falling on it is called the reflected ray. The point of the plane at which the incident ray strikes is called the point of incidence and the perpendicular drawn on the reflecting plane at that point is called the normal. In Fig. 1, XY is the reflecting plane while AO is the incident ray, A OB is the reflected ray and ON is the normal.
Laws of Reflection
Regular reflection of light from a reflecting plane takes place under the following two laws.
First law: The incident ray, normal and reflected ray all lie in a plane. This plane is called incident plane.
Second law: The angle between the normal to the reflecting plane and the incident ray is equal to the angle between the normal and the reflected ray. These angles are called angle of incidence and angle of reflection respectively and are represented by i and r. Thus,
Angle of incidence ∠i=Angle of reflection ∠r
Image
The light rays passing through a point after reflection or refraction meet or appear to meet at a point, then that point is called the image of the first point. By joining the images of all the points of an object of finite size,the complete image of that object is obtained.
Images are of two types: 1. Virtual, 2. Real
(1) Virtual Image: If the rays coming from a point object do not actually meet at any point reflection or refraction but if it appears to be coming from some point, then that point is called the virtual image of the first point. The virtual image cannot be obtained on the screen nor can it be photographed. The image obtained from a plane mirror is always virtual.
(2) Real Image: If the rays coming from an object after reflection or refraction meet at some other point, then that point is called real image of that object. The actual image can be obtained on the screen.
