They are basically of 2 types –1)Fixed Resistor and2)Variable ResistorsClassification of Resistors:From operating conditions point of view, resistors can be classified into two.1) Fixed resistors2) Adjustable/ variable resistors

1) Fixed resistors are further classified into:a) Carbon composition type resistors b) Metalized type resistors c) Wire wound type resistorsa) Carbon composition type resistors:This is the most common type of low wattage resistor. The resistive material is of carbon-clay composition and the leads are made of tinned copper. These resistors are cheap and reliable and stability is high.b)Wire wound resistors:These resistors are a length of wire wound an insulating cylindrical core. Usually wires of material such as constantan (60% copper and 40% nickel) and manganin which have high resistivities and low temperature coefficients are employed. The completed wire wound resistor is coated with an insulating material such as baked enamel.c) Metalized resistorsIt is constructed using film deposition techniques of depositing a thick film of resistive material onto an insulating substrate.Only approximate values of resistance can be had by this method.2) Variable resistorsFor circuits requiring a resistance that can be adjusted while it remains connected in the circuit(for eg: volume control on radio), variable resistors are required. They usually have 3 lead two fixed and one movable.

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