Ray optics is that part of optics which studies the motion of light by considering it as a ‘ray’. According to the assumption of ray optics, as long as light travels in a homogeneous medium, its path is a straight line. Where two mediums meet, the light rays are bent. Light is an electromagnetic wave (wavelength:- about 400 nm to 750 nm) that travels in a straight line in a vacuum with a very fast speed, c = 2.99792458 × 108 ms–1 (≅ 3 × 108 ms–1).
The Ray Model of Light
Our everyday experience that light travels in a straight line is the basis of the ray model of light. For example sunlight entering into a darkened room through a small hole, laser beams etc., moves in a straight line path. The ray model of light is valid as long as any apertures through which the light passes (lenses, mirrors, and holes) are very large as compared to the wavelength of light. In that case, diffraction and other wave aspects of light are negligible and can be ignored.
Some of the terms used in ray model of light:
- Light ray: A light ray is a straight line that represents the path of a beam of light traveling through a medium, such as air, water, or a lens. Light rays are often used in optics to represent the path of light and to determine how it will behave when it interacts with other materials.
- Light beam: A light beam is a collection of light rays that travel together in the same direction. Light beams are often used in optics to describe the intensity and direction of light.
- Pencil: A narrow beam of light is called a pencil. It refers to a group of light rays that originate from a single point. A pencil is of three types :
- Convergent pencil: A convergent pencil is a group of light rays that converge, or come together, at a single point after passing through a lens or other optical element. This results in an image that is smaller and closer to the lens than the object.
- Divergent pencil: A divergent pencil is a group of light rays that spread apart from a single point after passing through a lens or other optical element. This results in an image that is larger and farther away from the lens than the object.
- Parallel pencil: A parallel pencil is a group of light rays that are parallel to each other and do not converge or diverge. This type of pencil is often used in optics to model the behavior of light from distant sources, such as stars.
Note :- The main difference between a light beam and a pencil is in the way the light rays are distributed. A light beam is a collection of light rays that are traveling in the same direction and are generally parallel to each other. A pencil, on the other hand, is a group of light rays that originate from a single point and may be converging, diverging, or parallel to each other.
A mirror is an object that reflects light and forms an image of an object. It consists of a flat or curved surface that is made of a reflective material, such as glass with a silver or aluminum coating, or a polished metal surface. When light rays strike the surface of the mirror, they are reflected back, creating an image of the object in front of the mirror. In short A mirror is a reflective surface that light does not pass through, but bounces off of and this produces an image.
Types of Mirrors :-
There are mainly three types of mirrors:-
- Plain Mirror
- Spherical Mirror :- (1) Convex Mirror (2) Concave Mirror
- Parabolic Mirror