The resistance (R) of an object is the ratio of voltage across it to the current through it.
It’s a scalar quantity with an SI unit of ohm (æ) .
The resistance of a conductor is 1 ohm when a potential difference of 1 volt across the conductor produces current flow of 1 amp through it.
1 Æ 1 V A1 Resistance and energy loss
As electricity flows through a material it heats up that material.That energy conversion from electrical potential to heat depends on the resistance of the material. High resistance means that a large percentage of the electrical energy is lost as heat; low resistance means little energy is lost.
Resistor
RESISTOR A resistor is a device that converts electrical potential energy to some other form.
All conductors offer some resistance, so all conductors can be thought of as resistors. The circuit symbol for a (fixed) resistor is
Variable resistor (e.g. rheostat)
A variable resistor is one whose resistance can be varied (obviously!). The most common one is the rheostat, consisting of a high-resistance wire wound around a coil with a sliding contact. By adjusting the position of the sliding contact you are varying the length of wire that the current has to travel through. Resistance increases with the length of the resistor.
The circuit symbol for a variable resistor is
Measuring Resistance An ohmmeter can be used to measure resistance.
In order to measure the resistance of a component it is removed from the circuit and connected directly to the ohmmeter. Typically the laboratory ohmmeter is part of a digital multimeter.
The circuit symbol for an ohmmeter is A multimeter RESISTANCE 305
