Q.1 Define the term 'amorphous'.Give a few examples of amorphous solids.
Ans:- A solid is said to be amorphous if the constituent particles are not arraged in any regular manner.They may have only short range order.Some example of amorphous solid are glass,plastics,rubber etc.
Q.2 What makes a glass different from a solid such as quartz?Under what conditions could quartz be converted into glass?
Ans:- Quartz is a crystalline form of silica(SiO2).In it SiO4 tetrahedral are connected to another in such a way that oxygen atom of each SiO4 tetrahedron is shared with another silicon atom.If quartz or SiO2 is melted and the melt is cooled,glass is formed which is amorphous.In glass SiO2 tetrahedra are randomly joined.It is super cooled liquid.
Q1.17 what is a semiconductor?Describe the two main types of semiconductors and contrast conduction mechanism.
Ans:- Substances whose conductance lies between that of metals(conductors) and insulators are called semi-conductors.
Two main types of semi conductor are n-type and p-type.
n-type semi-conductors-
A Groups 14 elements like Ge,Si doped with group 15 elements such as P abs As are called n-type semi-conductors.The symbol 'n'indicating that negative charge flows in them.The group 15 elements have one excess valence electron(compared to Si or Ge) after forming the four covalent bonds normally formed by group 14 elements.The excess electrons give rise to electrical conduction.
p-type semi-conductors-
A group 13 element which has only three valence electrons forms an electron-deficient bond or a hole.Such holes can move across the crystal giving rise to electrical conductivity.Thus impurity doped Si and Ge are semi-conductors whose conductivity increases with increasing temperature unlike metals whose conductivity decreases with increase in temperature.Group 14 elements doped with group 13 elements are called p-type semi-conductors.The symbol 'p' is used because in an electrical field,the holes move through the crystal like positive charge,i.e.,in a direction opposite to the follow of electrons.
