Resistance is measured in Ohms
An Ohm is a resistance that produces a potential difference of one volt when a current of one ampere is flowing through it.
Resistance in a circuit reduces the current that can flow.
Resistors are used to ...
- reduce the current flowing in a circuit
- divide voltages (potential divider)
- ideal resistors behave in the same way for any frequency of signal.
Most resistors are designed to have a constant resistance over a wide temperature range.
Here are some exceptions ...
Light Dependent Resistor (LDR)
These are used to measure light level. If the light level increases, the LDR resistance decreases.
Temperature Dependent Resistors (TDR or Thermistor)
These are used to measure temperature.
Negative Temperature Coefficient thermistors reduce their resistance in response to increasing temperatures.
Devices like incandescent bulbs increase their resistance as the temperature rises. (Positive temperature coefficient).
Input Transducers
Devices like LDRs and TDRs, used to take measurements, are called Input Transducers