What is the SI unit of electrical resistance?
The SI unit of electrical resistance is the ohm (Ω). Electrical conductance is measured in siemens (S), which were formerly called the mho.
Questions about Electrical resistance and conductance
Short answers, pulled from the story.
How does wire length and thickness affect resistance?
A wire has higher resistance if it is long and thin, and lower resistance if it is short and thick. All objects resist electrical current except for superconductors, which have a resistance of zero.
Who discovered Joule heating and what is its formula?
Joule heating is named after James Prescott Joule and follows the formula P = I^2R. This phenomenon converts electrical energy into thermal energy to heat resistors or filaments.
Why do metals increase in resistivity as temperature rises?
Near room temperature, the resistivity of metals typically increases as temperature is increased while semiconductor resistivity decreases. Components that use this property are called resistance thermometers or thermistors.
What conditions allow superconductors to achieve zero resistance?
Superconductors require cooling to temperatures near 10 K with liquid helium for most metallic types like niobium. Ceramic high temperature superconductors need cooling to temperatures near 77 K with liquid nitrogen.