Resistors: Resistor is an electrical component that provides electrical resistance to a circuit. Resistors are used to decrease the flow of current. Principle of Resistors: Ohms law: Ohms law states that the voltage across the resistor is proportional to current, where the constant of proportionality is resistance. Symbols of resistors are: Here a= resistor, b= rheostat and c is potentiometer. Types of resistors 1. Power Resistors 2. Variable Resistors Effect of temperature in resistor: 1. Metal conductor Temp and resistance increases with increase in temperature. Rt=Ro(1+alpha0t) positive temperature cofficient 2. Semi conductor Temperature increases and resistance decreases with increase in temperature. Rt=Ro(1-alpha0t) negative temp coffecient 3. Isulator Temperature increases and resistance decreases with increase in temperature.