Why dispersion of light occurs

More Optics Questions Q1. In a convex lens, when the object is placed at infinity, where is the image formed? Which of the following refrective defects of vision is also known as Far-sightedness? The image formed by a convex mirror is:.

Which of the following is the heaviest ray? Which of the following is known as nearsigntedness? Which of the following types of glass can cut off ultraviolet rays? More Physics Questions Q1.

Which of the following is correct about sound? Large amplitude - Loud sound II. High frequency - Low pitch. Prism: Let us consider a detailed understanding of the same. In a triangular prism, the dispersion of the beam within the glass prism occurs.

This is further dispersed in the beam within the glass and we clearly observe the spectrum emerging from the other end of the prism.

Question Why does dispersion take place when light is passed through prism and not through glass slab? Asked by: Kavita Answer A light ray is refracted bent when it passes from one medium to another at an angle and its speed changes.

At the interface, it is bent in one direction if the material it enters is denser when light slows down and in the OTHER direction if the material is less dense when light speeds up. Because different wavelengths colors of light travel through a medium at different speeds, the amount of bending is different for different wavelengths. Violet is bent the most and red the least because violet light has a shorter wavelength, and short wavelengths travel more slowly through a medium than longer ones do.

Because white light is made up of ALL visible wavelengths, its colors can be separated dispersed by this difference in behavior. When light passes through glass, it encounters TWO interfaces--one entering and the other leaving. It slows down at the first interface and speeds back up at the second. If the two interface surfaces are parallel to each other, as in a 'slab' of glass, all of the bending and dispersion that takes place at the first interfaces is exactly reversed at the second, 'undoing' the effect of the first interface; so although the emerging ray of light is displaced slightly from the entering ray, it travels in the same direction as the incoming ray and all wavelengths that separated at the first interface are re-combined.

For instance for some types of glass, the n value for frequencies of violet light is 1. The absorption and re-emission process causes the higher frequency lower wavelength violet light to travel slower through crown glass than the lower frequency higher wavelength red light. It is this difference in n value for the varying frequencies and wavelengths that causes the dispersion of light by a triangular prism.

Violet light, being slowed down to a greater extent by the absorption and re-emission process, refracts more than red light. Upon entry of white light at the first boundary of a triangular prism, there will be a slight separation of the white light into the component colors of the spectrum. The amount of overall refraction caused by the passage of a light ray through a prism is often expressed in terms of the angle of deviation.

The angle of deviation is the angle made between the incident ray of light entering the first face of the prism and the refracted ray that emerges from the second face of the prism. Because of the different indices of refraction for the different wavelengths of visible light, the angle of deviation varies with wavelength.

Colors of the visible light spectrum that have shorter wavelengths BIV will deviated more from their original path than the colors with longer wavelengths ROY. The emergence of different colors of light from a triangular prism at different angles leads an observer to see the component colors of visible light separated from each other.

Of course the discussion of the dispersion of light by triangular prisms begs the following question: Why doesn't a square or rectangular prism cause the dispersion of a narrow beam of white light? The short answer is that it does. The long answer is provided in the following discussion and illustrated by the diagram below. Suppose that a flashlight could be covered with black paper with a slit across it so as to create a beam of white light.