Resistor 

A resistor is the two-terminal electrical device that implements electrical resistance like the circuit element. When the voltage “V” is applied across the terminals of the resistor, the current “I” would flow via the resistor in the direct proportion to that voltage. The common of the constant of the proportionality is called as resistance “R”, because, with the given V or voltage, a bigger value of R added resists the flow of the current “I” as given by the Ohm's law:

I = V/R

In other words, in a practical sense a resistor is a circuit component that is used because of its resistance. Mathematically, a resistor is a circuit component for which there is an algebraic relation between its instantaneous voltage and instantaneous current such as v = iR, the voltage-current relation for a resistor that obeys Ohm's law —a linear resistor. Any other type of voltage-current relation (r = Ai² + 6, for example) is for a nonlinear resistor. The term "resistor" usually designates a linear resistor. Nonlinear resistors are specified as such.

Substitution from V = IR into P = VI gives the power absorbed by a linear resistor in terms of resistance

Every resistor has a power rating, also called wattage rating that is the maximum power that the resistor can absorb without overheating to a destructive temperature.

Nominal Values and Tolerances

Manufacturers print resistance values on resistor casings cither in numerical form or in a color code. These values, though, are only nominal values: They are only approximately equal to the actual resistances. The possible percentage variation of resistance about the nominal value is called the tolerance. The popular carbon-composition resistors have tolerances of 20, 10, and 5 percent, which means that the actual resistances can vary from the nominal values by as much as ±20, + 10 and +5 percent of the nominal values.

Questionnaire:

• What is Resistor? Explain
• Give the Ohm's law formula for resistors.