# Electrical resistance and heat relationship

### Joule heating - Wikipedia The power electrically dumped into a resistor is: P = I2R = V2/R The only thing a resistor can do with that power is turn it into heat. However. Hence the heating effect produced by an electric current, I through a conductor of resistance, R for a time, t is given by H = I2Rt. This equation is called the. The electrical resistance of an object is a measure of its opposition to the flow of electric current. . This relationship is called Ohm's law, and materials which obey it are called ohmic materials. Examples of ohmic .. This electrical energy is dissipated, heating the resistor in the process. This is called Joule heating (after. For example, there may be a large water pressure above the pipe, which tries to push water down through the pipe. But there may be an equally large water pressure below the pipe, which tries to push water back up through the pipe.

### Temperature effects on resistance

If these pressures are equal, no water flows. In the image at right, the water pressure below the pipe is zero. The resistance and conductance of a wire, resistor, or other element is mostly determined by two properties: 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.

### What is the relationship between Heat and Resistance and why? - Embibe

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. Therefore, the two resistors are ohmic, but the diode and battery are not.

## Joule heating

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 may be expected to happen because, as temperature changes, the dimensions of the conductor will change as it expands or contracts. Materials used for practical insulators glass, plastic etc. They remain good insulators over all temperatures they are likely to encounter in use. These changes in resistance cannot therefore be explained by a change in dimensions due to thermal expansion or contraction.

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. 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. 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.

The effect of heat on the atomic structure of a material is to make the atoms vibrate, and the higher the temperature the more violently the atoms vibrate.