Why insulators are transparent

These electrons reradiate the light in the direction opposite from which it arrived reflection , but they interfere with the light that would proceed in the forward direction, preventing transmission. She adds some details about the role of physical structure: "A material appears transparent when it does not strongly absorb or diffract light.

As far as the absorbance of a solid goes, you pretty much have to take what Nature gives you. Diffraction, however, can be influenced by how the material is prepared.

The boundaries between these regions are called grain boundaries. If the distance between boundaries is smaller than the shortest wavelength of visible light in other words, if the refractive index of the material is uniform with respect to the light passing through it , then the material will appear transparent. Each boundary tends to diffuse the light that passes through; if the regions are small enough, however, the light waves essentially 'jump' right over them.

It has no internal grain boundaries, and hence it looks transparent. Solid silicon dioxide sand , in contrast, has obvious grain boundaries, so it is not transparent. One way to do this is to press a material under force, as is done all the time with potassium bromide, a compound used for infrared spectroscopy in laboratories.

The other way to achieve uniformity is to create lots of nucleation sites the locations where crystals begin to form in a melted material and then allow it to cool. Because many little crystals begin to form all at once, none of them can grow very large before they run into one another. Learn more. Why aren't all insulators transparent, since they have a large band gap? Ask Question. Asked 4 years, 2 months ago. Active 4 years, 2 months ago. Viewed times. As electrical insulators generally have a large band gap, why aren't all insulators transparent?

Improve this question. Kawin M Kawin M 4 4 silver badges 16 16 bronze badges. For example, sapphire crystalline aluminum oxide is wonderfully transparent, while alumina-based ceramics often are not due to grain sizes and impurities. Add a comment. Conductors such as gold, silver and copper have low resistance and conduct electricity easily. Insulators such as rubber, glass and ceramics have high resistance and are difficult for electricity to pass through.

Semiconductors have properties somewhere between these two. Their resistivity might change according to the temperature for example. At a low temperature, almost no electricity passes through them. But when the temperature rises, electricity passes through them easily.

Semiconductors containing almost no impurities conduct almost no electricity. But when some elements are added to the semiconductors , electricity passes through them easily. Semiconductors comprising a single element are called elemental semiconductors , including the famous semiconductor material Silicon. On the other hand, semiconductors made up of two or more compounds are called compound semiconductors , and are used in semiconductor lasers, light-emitting diodes , etc.

An atom is consisting of a nucleus and electrons orbiting the nucleus. The electrons cannot orbit the nucleus at any distance in the atomic space surrounding the nucleus, but only certain, very specific orbits are allowed, and only exist in specific discrete levels. These energies are called energy levels. A large number of atoms gather to form a crystal, and interacts in a solid material, then the energy levels became so closely spaced that they form bands. This is the energy band.

Metals, semiconductors and insulators are distinguished from each others by their band structures. Their band structures are shown in the figure below. This means that the metal always has electrons that can move freely and so can always carry current. Such electrons are known as free electrons. These free electrons are responsible for current that flows through a metal.