Question

a) Explain the property of light that can be shown from the above activity.







































a) Explain the property of light that can be shown from the above activity.

Answer 1

Explanation:

EENS 2110 Mineralogy

Tulane University

Prof. Stephen A. Nelson

Properties of Light and Examination of Isotropic Substances

This document last updated on 17-Oct-2014

The optical properties of crystals are, next to x-ray diffraction and direct chemical analyses, the most reliable properties available to distinguish and identify minerals. The optical properties depend on the manner that visible light is transmitted through the crystal, and thus are dependent on crystal structure, crystal symmetry, and chemical composition of the mineral.

In order to understand the optical properties of crystals we must first understand something about light and how it interacts with matter.

Light

Light is electromagnetic radiation that has properties of waves. The electromagnetic spectrum can be divided into several bands based on the wavelength. As we have discussed before, visible light represents a narrow group of wavelengths between about 380 nm and 730 nm.

Our eyes interpret these wavelengths as different colors. If only a single wavelength or limited range of wavelengths are present and enter our eyes, they are interpreted as a certain color. If a single wavelength is present we say that we have monochromatic light. If all wavelengths of visible light are present, our eyes interpret this as white light. If no wavelengths in the visible range are present, we interpret this as dark.

Interaction of Light with Matter

Velocity of Light and Refractive Index

The energy of light is related to its frequency and velocity as follows:

E = hν = hC/λ

where E = energy

h = Planck's constant, 6.62517 x 10-27 erg.sec

ν = frequency

C = velocity of light = 2.99793 x 1010 cm/sec

λ = wavelength

The velocity of light, C, in a vacuum is 2.99793 x 1010cm/sec. Light cannot travel faster than this, but if it travels through a substance, its velocity will decrease. Note that from the equation given above-

C = νλ

The frequency of vibration, ν, remains constant when the light passes through a substance. Thus, if the velocity, C, is reduced on passage through a substance, the wavelength, λ, must also decrease.

We here define refractive index, n, of a material or substance as the ratio of the speed of light in a vacuum, C, to the speed of light in a material through which it passes, Cm.

n = C/Cm