The visible light is in the very narrow region of electromagnetic spectrum. The visible light waves can be detected by human eye. The frequency of visible light waves is ranging from 4 × 1014 Hertz to 8 × 1014 Hertz. The wavelength range of visible light waves lies between 400 nanometer to 700 nanometer. The visible light waves consists of seven colored light such as violet, indigo, blue, green, yellow, orange, red. The visible light waves are produced by atomic excitation. The visible light waves emitted or reflected from objects around us provide the information about the world surrounding us.
(i) The visible light waves are produced by accelerating or oscillating charged particles.
(ii) The visible light waves do not require any material medium for their propagation.
(iii) The visible light waves are transverse in nature.
(iv) The visible light waves travel in free space with a speed of 3 × 108 metre per second.
(v) In visible waves the sinusoidal variation in both electric and magnetic fields vectors occurs simultaneously.
(vi) The direction of electric and magnetic fields variations are perpendicular to each other.
(vii) The velocity of visible light waves depends entirely on the electric and magnetic properties of the medium in which they travel and is independent of the amplitudes of the field vectors.
(viii) The velocity of visible light waves in any dielectric medium is less than 3 × 108 metre per second.
(ix) The visible light wave carry energy, which is, divided equally between electric field and magnetic field vectors.
(x) The electric field vector is responsible for the optical effects of an electromagnetic wave and it is called as light vector or optic vector.
Light is a form of energy that produces the sensation of vision. Light itself invisible. When it falls on an object the scattered light enters the eye and the object becomes visible. In this process the light undergoes modifications exhibiting its properties. Optics is the study of these interactive properties of light. The path along which light energy travels is called a ray. In a homogeneous medium a ray may be represented by a straight line with an arrow head in the direction in which the energy travels. The study of light based on the concept of rays with the help of geometrical principles is called Geometrical Optics.
Geometrical optics is based on three general laws . (1) The law of rectilinear propagation of light. (2) The laws of reflection . (3) The laws of refraction.
Law of rectilinear propagation of light : In a homogeneous medium light travels along a straight line.
(I) a part of the light comes back into the same medium from the surface in a definite direction. This part of the light is called reflected part and this phenomenon is called reflection.
(ii) Another part of the light enters the second medium at the surface which is the refracted part and the phenomenon is called refraction.
1) When the separating surface is plane, a parallel beam of light incident on it will remain parallel even after reflection as shown in the figure below. This type of reflection is said to be regular. Reflection from a plane mirror is an example of this type.
2) If the separating surface is uneven, the normal at different points will be in different directions. But the incident rays of light at different points obey the laws of reflection. So, the rays that were parallel before reflection will be reflected in random directions as shown ind the second figure above. This kind of reflection is called diffuse reflection. We can see an object due to diffuse reflection of light by the object.
Refraction of light is the bending of light when it travels from one medium to another medium. The various phenomena that occur when light travels from one medium to another medium. If the second medium is denser with respect to the first, then according to Snell , sin(i) / sin(r) = v1 / v2 . Where i , r are the angles of incident and refracted rays, v1 , v2 are the velocities of light in the two media.