The electric conductivity of bodies is directly connected with mobility of the main carriers of a charge. Therefore change of conductivity can happen by means of impact on charges in substance.
It is required to you
- The textbook in physics, the sheet of paper, a simple pencil, a glass of water, salt, the glow lamp.
Instruction
1. Open the textbook by physics on a subject of resistance of materials. The classical theory claims that in various substances the ways of the organization of electric conductivity are various, however they at all have something the general - it is free carriers of a charge. Thus, it is possible to change conductivity, first of all, changing the number of free carriers of a charge.
2. Remember that semiconductor substances represent and how in them the electrical resistance (conductivity) is formed. It is known that in semiconductor substances carriers of a charge are or the electrons which left for any reasons an orbit of the atom, or "holes" left after leaving from their place of electrons. Thus, two types of carriers of a charge turn out. Therefore, having increased number of electrons, it is possible to increase conductivity of a body. In the main way as it can be done, heating of a body is. Heating the semiconductor, it is possible to increase concentration as free electrons which escape from the places under the influence of heat, and "holes" left the free electrons which left them now.
3. Pay attention that not in all substances the electric conductivity is carried out by electrons. There is a number of substances which have rather good conductivity comparable with conductivity of metals, at the expense of ions of any substance. Take the ordinary glow lamp and turn on it in an electrical circuit in which instead of a key use a gap with two contacts omitted in a glass with the distilled water. You will find out that the lamp does not shine. It means that water is a dielectric. Now, without disconnecting a lamp from a current source, fill salt in water. You will see that brightness of a luminescence of a lamp increases that speaks about increase in conductivity of water. The reason of this phenomenon is that at dissolution of salt in water the last becomes electrolyte because atoms of salt break up to ions of sodium and chlorine which provide conductivity of substance.
4. It is worth noticing that the conductivity of metal cannot be increased or reduced in the above ways because it is impossible to change quantity of free electrons in metal. The main way to change conductivity of metal is to change its geometrical sizes. For increase in electric conductivity of metal it is possible to reduce length of the metal conductor or to increase cross-sectional area. It in the ways it is possible just to reduce number of collisions of free electrons with knots of a crystal lattice of metal, thereby reducing its resistance.