Material Science Exc.1 Flashcards
What is mathessien’s rule?
Resistances resulting from independent scatterings are additive. We can solve it by adding the residual resistivity, which is independent of temperature but is dependent on scatterings and defect and adding the phonon resistivity which is dependent on the temperature.
What is alpha of resistance?
Alpha refers to the temperature coefficient of resistance. It measures the realtive change in resistance per degree change in temperature. For most metals it’s positivie which means that with increase of temperature, the resistivity increases too. For semiconductors or insulators it’s negative, so the resistance decreases as temperature increase.
How does temp. influence resistivity/resistance of metals?
As the temp rises in metals, atoms vibrate more which affect the flow of electrons in metal, that causes more collisions, so the resistance gets bigger with the temp. This happens because pf their lattice structure, where the positive ions are arranged. As the temperature decreases, atoms vibrate less, so the resistance is getting lower as the temp. decrease, which allow the electrons to move freely through the structure of metals. At some materials resistivity may drop to zero, which makes them superconductive
How current flows in a electrical circuit
It flows through the circuit, the circuit needs voltage, electric charge, resistance and conductor. The electric current is carried by free electrons through the wires (made of copper usually) from the negative terminal to the positive.
How does electric field effect electrons resistivity of metals?
It influences the motion of electrons. When it’s applied, it creates force that pushes free electron in a specific direction, the movement we observe is electric current. Resistivity of metal depends on collisions. Electrical field can increase the current, which leads to increase of the temperature, so the resistance also grows. This leads to more frequent collisions of atoms.
