Resistor
The resistor is used to measure the control the amount of current that flows through a circuit. The value and tolerance of the resistor is given by the four coloured bands on the resistor. The colours of the first three bands indicate the first digit, the second digit and the number of zeros that follow the first two digits. The fourth band indicates the tolerance of the resistor: brown = ± 1%, red = ± 2%, gold = ± 5%, silver = ± 10%, none = ± 20%.
The power rating of a resistor is the maximum rate of dissipation of electrical energy as heat before it is damaged. A rating of 0.25 W to 1W is the most common.
Potential Divider
A potentiometer is a variable potential divider. It consists of a resistor connected across a voltage source.
Thermistor
Is a device whose resistance is affected by temperature. Its’ resistance decreases with increasing temperature. It is used in applications such as temperature control, temperature measurement and fire alarms.
Light dependent resistor
The resistivity of a L.D.R. depends on the light intensity acting on it. The resistance decreases with an increase of light.