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The red curve shows the power in the load, normalized relative to its maximum possible. The dark blue curve shows the efficiency η. The efficiency η is the ratio of the power dissipated by the load resistance R L to the total power dissipated by the circuit (which includes the voltage source's resistance of R S as well as R L):
The voltage drop across the load is proportional to the power available to be converted in that load to some other useful form of energy. For example, an electric space heater may have a resistance of 10 ohms , and the wires that supply it may have a resistance of 0.2 ohms, about 2% of the total circuit resistance.
Resistivity, density, and resistivity-density products of selected materials Material Resistivity (nΩ·m) Density (g/cm 3) Resistivity × density Resistivity relative to Cu, i.e. cross-sectional area required to give same conductance Approx. price, at 9 December 2018 [dubious – discuss] (g·mΩ/m 2) Relative to Cu (USD per kg) Relative to Cu ...
Also called chordal or DC resistance This corresponds to the usual definition of resistance; the voltage divided by the current R s t a t i c = V I. {\displaystyle R_{\mathrm {static} }={V \over I}.} It is the slope of the line (chord) from the origin through the point on the curve. Static resistance determines the power dissipation in an electrical component. Points on the current–voltage ...
The electrical resistance of a uniform conductor is given in terms of resistivity by: [40] = where ℓ is the length of the conductor in SI units of meters, a is the cross-sectional area (for a round wire a = πr 2 if r is radius) in units of meters squared, and ρ is the resistivity in units of ohm·meters.
Power sources have curves passing through the red regions. Active vs passive: Devices which have I–V curves which are limited to the first and third quadrants of the I–V plane, passing through the origin, are passive components (loads), that consume electric power from the circuit. Examples are resistors and electric motors.
For a given amount of power, a higher voltage reduces the current and thus the resistive losses. For example, raising the voltage by a factor of 10 reduces the current by a corresponding factor of 10 and therefore the I 2 R {\displaystyle I^{2}R} losses by a factor of 100, provided the same sized conductors are used in both cases.
A field level (or root-power level) is a logarithmic quantity used to measure quantities of which the square is typically proportional to power (for instance, the square of voltage is proportional to power by the inverse of the conductor's resistance), etc., with commonly used units neper (Np) or decibel (dB).