Question

Carbon resistors are of two types:

A. Composition type resistor and film type resistor
B. Rheostat and film type resistor
C. Rheostat and variable resistor
D. Composition type resistor and rheostat.

Answer 1

Hint: Resistors are to be manufactured in a way that it should ensure large high value resistances, increased resistive path and more precision.

Complete step by step answer:Carbon resistors are cheap resistors used for general causes. The resistive elements in these resistors are made from a mixture of finely ground carbon dust or graphite and a non-conducting ceramic powder (like clay) to bind it all together.
This is made into cylinders with leads or metallic wiring that are attached to each end. This enhances the electrical connection. Further, it is coated with an outer insulating material and colour coded markings to denote its resistive value.

Carbon resistors are of two types:

Carbon composition resistors: they are low inductance resistors of low-to-medium type power. The resistive element is synthesised by mixing carbon that is finely powdered, with an insulating material like ceramic. This is held together by a resin. They are ideal for high frequency applications. They were commonly used in electrical circuits as it is cheap. But they have very large tolerances and it can also suffer from noise when it gets hot. Hence, it is used less frequently.

Carbon film resistors: These resistors use carbon film deposition on a ceramic former for resisting current. They are helical in shape and the substrate on which the film is deposited, acts as an insulator. Its resistive value can be controlled by increasing the thickness of the film that is deposited.

Hence, the correct option is option A.

Note:The manufacturing process of carbon composition type resistors result in large tolerance values. Hence, carbon film type resistors were developed as an alternative. But film resistors have a large value of negative temperature coefficient which is a major drawback of this resistor that owes to the usage of pure carbon during its preparation.