Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight.
the term light sometimes refers to electromagnetic radiation of any wavelength, whether visible or not.
Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz.
In this chapter you will learn about the reflection, refraction and other different phenomena of light. There are a number of common wonderful phenomena associated with light such as image formation by mirrors, the twinkling of stars, the beautiful colours of a rainbow , bending of light by a medium and so on. A study of the properties of light helps us to explore them.
1.Nature of light
light is the form of energy that gives us sensation of vision.
2.Newton’s copuscular theory
According to newton, light travels in form of corpuscle(particle) to some phenomena such as rectilinear propagation. reflection, rarefraction can b explained on the basis of this theory. but some other phenomena such as interference , defraction, polarisation cannot be explained, so this theory is not accepted.
3.Huygen’s wave theory
according to this theory, light travels in form of waves to maximum phenomena can be explained but some other phenomena such as photoelectric effect, crompton effect and black body radiation cannot be explained, so this theory is also not widely accepted.
4.Einsteen or quantum theory(modern theory):
according to this theory, light travelsin form of particles and one wave is also associated with it. so, light possesdual nature. so this theory is able to explain all phenomena.
5.Laws of reflection:
1.the angle of incidence is equal to the angle of reflection.
2.the incident ray, the normal to the plane at the point of incidence and the reflected ray all lie in the same plane.
6.Properties of image formation by a plane mirror:
1.image is always virtual.
2.image is erect but laterally inverted.
3.image is of the same size as the size of object.
4.image is formed behind the mirror at the same distance as object lies at the front of the mirror.
5.to see our complete image, the minimum size of the mirror should be half of that object.
6.if mirror is rotated by 0(theta) degree then the reflected rays will be deviated by 20(theta) degree.
7.if 2 mirrors asr allinged by angle 0(theta) then the number of images formed by these 2 mirrors will be ezual to 360/0(theta).
7.Rules for formation of image by a spherical mirror:
1.rays passing through the centre of curvature reflect back in same direction.
2.rays parallel to principle axis passes through focus.
3.rays passing through focus will become parallel to principle axis.
4.rays falling on pole will obey laws of reflection.
when light falls on any polished surface it returns back in same medium, obeying some definite laws, this phenomena of light is known as reflection of light.
the miror whose reflecting surface is curved is called a spherical mirror. it may be curved inward or outward.
in a concave mirror the outer surface is polished and the inner surface is used for reflection.
in a convex mirrir the inner surface is polished and the outer surface is used for reflection.
pole is the centre of any spherical mirror.
principle axis is any imaginary line joining the centre of curvature and pole.
the rays that are parallel to the principle axis, after reflection from mirror meet or tends to meet at a point on the principle axis is known as focus.
2.8.Centre of curvature
centre of curvature is the centre of that sphere from which mirror is taken as a part.
focal lenght is the distance between the pole and focus.
the diameter of the mirror is known as aperture
2.11.Radius of curvature
the distance between the centre of curvature and pole or it is a radius of that sphere from which mirror is taken as a part.
when light undergoes from one medium to another medium it deviates from it’s path. this phenomena is known as refraction of light.
bending of light depends upon the relative density between pair of medium.