(b) What is the difference between a dye and a pigment?.
Pigments are colour additives which are insoluble in the medium to which is added. Dyes are also colour additives, which are soluble in the medium to which it is added to: Water, Alcohol, Glycerine or oils. The difference is that a dye will dissolve in some suitable liquids where as a pigment wouldn't. .
2) Why do we see objects as coloured, in particular what part do absorption, reflection and transmission of light play?.
The colour of anything we observe depends upon a few factors. Everything is made up of electrons and atoms. Those atoms and electrons govern how something will look when in light. Any objects by its nature will, when exposed to light do one of the following:.
v Reflect or scatter light (Reflection and Scattering).
v Absorb light (Absorption).
v Do nothing (Transmission).
v Refract light (Refraction).
Reflection and Scattering.
A lot of objects reflect light to some degree, however something that is particularly reflective, has more fee electrons that are able to pass from atom to atom with ease. The light energy that is absorbed by these electrons is not passed onto any other atoms. Instead the electrons vibrate and the light energy is sent out of the material at the same frequency as the original light coming in.
Absorption.
When something appears to have no reflection or is opaque, the incoming light source frequency is the same as, or very close to, the vibration frequency of the electrons in the given material. The electrons of the material absorb the energy of the light source, and because the light is absorbed, the material or object appears opaque - has very little or no reflection.
Transmission.
This occurs when the energy of the incoming light is either much lower or much higher then the energy or frequency required to make the electrons in the particular material vibrate. Because of this the electrons, instead of capturing the light energy, let the light wave pass through the material unchanged, thus the material is transparent to that frequency of light.
