Almost all of the electrical conductors are made of metal or metal. But there is no material that can be a pure conductor. But some metals conduct electricity better than others. Silver, copper, and aluminum is a good conductor. Iron, steel, and coal can also conduct electricity, but the resistance is very high. Charcoal (carbon) is often used in electrical circuits, but it is not a good conductor.
Very poor conductor commonly referred to as a resistor or resistance or custody or inhibitors. Resistors have no free electrons or very few free electrons in the atom. So it is very difficult for the free electrons to move through the other atom deep. Resistor or detention is the electrical material that has low electrical conductivity or have a high resistance. Due to the high value of the resistor resitansinya often used as a barrier electric current.
Electrical materials are often used as resitor is charcoal or carbon, and nichrom.Dalam practice for the purpose of controlling the electric current used practical resistors are designed in a variety of prices. Practical unit of the resistor is Ohm.
Figure 3.5 Resistor
Electrical resistance is measured in ohms. Where ohms stating the amount of resistance in an electrical circuit. Resistance of one ohm allow for emf of one volt which causes the flow of current through the circuit of one ampere. The symbols used to express the unit ohm is Ω. The value of the electrical resistance on a conductor depend on the following four aspects:
The materials used
The diameter or size of the conductor
The length of conductors
conductor temperature
The value of the resistance of a conductor can be calculated using the equation:
Where :
R: conductor resistance, measured in ohms
ρ: resistivity of the material, in units ohm.mm 2 / m
l: length of the conductor, measured in meters (m)
A: cross sectional area of the wire conductor, in mm 2
Effect of Temperature on the value of is resistant is
– Raise the resistivity niali introduction of pure metals and alloys
– Lower the resistivity value of non-metallic conductors such as electrolyte and carbon as well as insulating materials such as paper, rubber, glass and mica.
For example, a temperature t0 resistor has a resistance R0. When the temperature rose to t1 resistor, then the resistance value increased to Rt. In this case there keanikan milai resistance of dR, where:
Where
α is a constant called the temperature coefficient
dt is the amount of temperature increase (t1 – t0)
So it can be written:
This temperature effect was also occurs in the value of the resistivity of the metal conductor materials (lead, sodium, copper and aluminum). Suppose the value t0 resitivitasnya is ρ0, then at t1 becomes ρ1.