Question

The Maxwell Equations for an EM wave in different (transparent) media show that the speed and wavelength of the wave change in different media, but the frequency is constant. An EM wave incident on an interface between two media will, in general, have a reflected and refracted part. The refracted rays obey Snell’s Law. The reflected rays obey the Law of Reflection. Illustrate the two laws with a diagram of a ray on a surface and clearly identify the angles involved. Explain the phenomenon of dispersion and why it occurs.

Answer 1

a) Snell's law

Snell’s law tells us the degree of refraction and relation between the angle of incidence, the angle of refraction and refractive indices of given pair of media. We know that light experiences the refraction or bending when it travels from one medium to another medium. Snell’s law predicts the degree of the bend. It is also known as the law of refraction. In 1621, Willebrord Snell discovered the law of refraction, hence called Snell’s law.

Definition: The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant, for the light of a given colour and for the given pair of media”

Sin i /Sin r =

b) Laws of Reflection

1) The law of reflection defines that upon reflection from a smooth surface, the angle of the reflected ray is equal to the angle of the incident ray, with respect to the normal to the surface that is to a line perpendicular to the surface at the point of contact.

2) The reflected ray is always in the plane defined by the incident ray and the normal to the surface at the point of contact of the incident ray.

Definition: The principle when the light rays falls on the smooth surface, the angle of reflection is equal to the angle of incidence, also the incident ray, the reflected ray, and the normal to the surface all lie in the same plane.

3) The splitting of white light into its constituent colours as it passes through a refracting medium (such as prism) is known as dispersion. We see about six colors in a rainbow—red, orange, yellow, green, blue, and violet; sometimes indigo is listed, too. Those colors are associated with different wavelengths of light. When our eye receives pure-wavelength light, we tend to see only one of the six colors, depending on wavelength. The thousands of other hues we can sense in other situations are our eye’s response to various mixtures of wavelengths. White light, in particular, is a fairly uniform mixture of all visible wavelengths. Sunlight, considered to be white, actually appears to be a bit yellow because of its mixture of wavelengths, but it does contain all visible wavelengths. The sequence of colors in rainbows is the same sequence as the colors plotted versus wavelength What this implies is that white light is spread out according to wavelength in a rainbow. Dispersion is defined as the spreading of white light into its full spectrum of wavelengths. More technically, dispersion occurs whenever there is a process that changes the direction of light in a manner that depends on wavelength. Dispersion, as a general phenomenon, can occur for any type of wave and always involves wavelength-dependent processes.