Temperature Coefficient of Resistance | Physics Of Conductors And Insulators | Electronics Textbook
There are several factors that affect the resistance of a wire. Electrical The temperature of the wire. The type of . You can think of the difference as between running through a deserted street and fighting your way through a crowded street . The electrical resistance of an object is a measure of its opposition to the flow of electric current. The inverse quantity is electrical conductance, and is the ease with which an electric current passes. Electrical resistance shares some conceptual parallels with the notion of . The difference between copper, steel, and rubber is related to their. Conduction: S. Gray, — Resistance: Georg Simon Ohm, Regular . In the case of copper, the relationship between resistivity and temperature is.
Just as all materials have a certain specific resistance at 20o Cthey also change resistance according to temperature by certain amounts. For pure metals, this coefficient is a positive number, meaning that resistance increases with increasing temperature.
Electric Resistance – The Physics Hypertextbook
For the elements carbon, silicon, and germanium, this coefficient is a negative number, meaning that resistance decreases with increasing temperature. For some metal alloys, the temperature coefficient of resistance is very close to zero, meaning that the resistance hardly changes at all with variations in temperature a good property if you want to build a precision resistor out of metal wire! The following table gives the temperature coefficients of resistance for several common metals, both pure and alloy: Setting up a table of voltage, current, and resistance values we get: At 20o Celsius, we get If the temperature were to rise to 35o Celsius, we could easily determine the change of resistance for each piece of wire.
Compare the wires in these experiments with the one from the previous page. It is shown again in Fig. In 10 seconds, 30 blue 'Coulomb-spheres' reach the end of the wire. The current is 3 amps Amps or amperes A are the SI unit of current.
One amp is equal to one coulomb per second. Current flow in a copper wire. It can be supplied by a battery and is measured in units of volts. EMF pushing the electrons through the wires remains the same. Length of the wire It is easier to blow through a short straw than through a long one. This is because a short straw offers less friction Friction is a force that acts between objects that are sliding over each other.
The direction of the force of friction is always such that it resists the motion. The experiment in Fig.
The wire in Fig. As before, time a 10 second period and count the number of coulombs Coulombs C are the SI unit of charge.
One coulomb is the equivalent of 6. The difference between copper, steel, and rubber is related to their microscopic structure and electron configurationand is quantified by a property called resistivity.
In addition to geometry and material, there are various other factors that influence resistance and conductance, such as temperature; see below.
Temperature effects on resistance
Conductors and resistors[ edit ] A 6. An ohmmeter could be used to verify this value. Substances in which electricity can flow are called conductors. A piece of conducting material of a particular resistance meant for use in a circuit is called a resistor.
Electrical resistance and conductance
Conductors are made of high- conductivity materials such as metals, in particular copper and aluminium. Resistors, on the other hand, are made of a wide variety of materials depending on factors such as the desired resistance, amount of energy that it needs to dissipate, precision, and costs. Ohm's law The current-voltage characteristics of four devices: Two resistorsa diodeand a battery. The horizontal axis is voltage dropthe vertical axis is current. Ohm's law is satisfied when the graph is a straight line through the origin.
Relationship between Resistance and Temperature
Therefore, the two resistors are ohmic, but the diode and battery are not. For many materials, the current I through the material is proportional to the voltage V applied across it: Therefore, the resistance and conductance of objects or electronic components made of these materials is constant.
This relationship is called Ohm's lawand materials which obey it are called ohmic materials.