Electric Resistance – The Physics Hypertextbook
I need to create a function to calculate the electrical resistance of graphite given some temperature for modeling a brushed DC motor. Google. Since the electrical resistance of a conductor such as a copper wire is dependent upon collisional proccesses within the wire, the resistance could be expected. In an ohmic conductor (one that follows Ohm's law), electric resistance varies Originally Answered: What is relation between resistance and temperature?.
In the same way, a long, thin copper wire has higher resistance lower conductance than a short, thick copper wire. Materials are important as well. A pipe filled with hair restricts the flow of water more than a clean pipe of the same shape and size. Similarly, electrons can flow freely and easily through a copper wire, but cannot flow as easily through a steel wire of the same shape and size, and they essentially cannot flow at all through an insulator like rubberregardless of its shape.
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. 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.
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. Type the name of the material and click the Submit button to find its resistivity. Mathematical Nature of Resistance Resistance is a numerical quantity that can be measured and expressed mathematically. The standard metric unit for resistance is the ohm, represented by the Greek letter omega. The equation representing the dependency of the resistance R of a cylindrically shaped conductor e.
Consistent with the discussion above, this equation shows that the resistance of a wire is directly proportional to the length of the wire and inversely proportional to the cross-sectional area of the wire. As shown by the equation, knowing the length, cross-sectional area and the material that a wire is made of and thus, its resistivity allows one to determine the resistance of the wire.
Resistors are one of the more common components in electrical circuits. Most resistors have stripes or bands of colors painted on them.Effect of Temperature on Resistance
The colors reveal information about the resistance value. Perhaps you're doing a lab and need to know the resistance of a resistor used in the lab.
In fact for a given size of conductor the change in resistance is due mainly to a change in the resistivity of the material, and is caused by the changing activity of the atoms that make up the material.
Temperature and Atomic Structure The reasons for these changes in resistivity can be explained by considering the flow of current through the material.
- Electrical resistance and conductance
- Temperature Coefficient of Resistance
- Relationship between Resistance and Temperature
The flow of current is actually the movement of electrons from one atom to another under the influence of an electric field.
Electrons are very small negatively charged particles and will be repelled by a negative electric charge and attracted by a positive electric charge.
Relationship between Resistance and Temperature - Basics of Electrical Engineering
Therefore if an electric potential is applied across a conductor positive at one end, negative at the other electrons will "migrate" from atom to atom towards the positive terminal. Only some electrons are free to migrate however. Others within each atom are held so tightly to their particular atom that even an electric field will not dislodge them. The current flowing in the material is therefore due to the movement of "free electrons" and the number of free electrons within any material compared with those tightly bound to their atoms is what governs whether a material is a good conductor many free electrons or a good insulator hardly any free electrons.