INDEX

RESISTOR
Resistors offers a resistance to the flow of current. Mainly resistors are classified according to
their resistance values and their power ratings. Resistances range from 10 ohm to 56Mohm(or more) and power ratings from 1/8W to 20W. We mostly use resistance in this range even though more power rating high value resistors are available. So when you select a resistor its value and power rating should be the deciding parameter. Normally available resistors are 1/8W, you can see this type of resistors in the resistance box which contain resistances from 10 ohm to around 56Mohm, costs
around Rs.30. But this resistor leads are flexible such that it will get bend easily. These 1/8W resistors are used in low power devices. The one which available in shops are of 1/4W which we
mainly use. P=I^2 * R, heat dissipation on resistor depends on the current flowing through it. Therefore for high current operations we use resistance of higher current ratings.The size of the resistor determines its power rating. Suppose if u put a resistor series with a motor which have a rating of 250mA(DC motor) -600mA(Stepper motor), then you can see that P=I^2R=.25^2*R=.0625R. Assume R=10 ohm then P=.625W >1/2W. In this case you have to use a resistor of about 1W or more. There are two types of resistors - fixed and variable.