Resistor is a component that opposes the flow of electric current and is measured in units called ohms. The bigger its value the more the resistance, they only consume power, that’s why they are referred to as passive components. Resistors are used for many purposes such as telephone equipment, electric heaters and current limiting devices. They are usually in different shapes and sizes. They may be standard, static resistor or special valuable resistors.
They are constructed from different variety of materials that is, carbon, metal and metal oxide films. A conductive material is wrapped in a helix around and then covered with an insulating material. Some of the standards, through-hole and no-frills resistors may have a composition of metal-film or carbon-film. Resistors are used with other component such as capacitors and inductors so that they can process signals in different ways
From their operating conditions, resistors can be classified in two types fixed and variable resistors.
They are further classified to metalized, wire wound and carbon composite type.
Wire wound resistor
They are lengths of wire would on an insulating cylindrical core. These resistors have materials such as constantan and manganin which have high resistivity’s and low coefficients. It’s coated with an insulating material such as baked enamel.
The metallic film resistors have a lower noise, better temperature stability and better for high frequency or radio frequency applications. Their construction is by film deposition techniques by depositing thick film of resistive material onto an insulating substrate.
Carbon composite type
Its resistive material is made of carbon-clay composition and the leads are made of tinned copper. As they are cheap and reliable, they are considered to be the most common type of low wattage with a high stability.
They are employed mostly to circuits which require adjustment while still connected to the devices. Types of variable resistors are;
Potentiometer It consist of two fixed and one changeable terminals. The two fixed are connected to the track and the third is connected to the sliding wiper. To change the potentiometer’s resistance, the wiper is moved over the resistive path. When its resistance is increased the electric current flowing through it will decrease and vice versa happens.
Its resistance changes when the temperature surrounding it change. The two types of thermistor are positive and negative temperature co-efficient. The negative thermistor decrease when the temperature increases while the positive one increases when the temperature increases.
Its resistance changes when the magnetic field is applied. Whenthe strength of the magnetic field applied to itis decreased, its resistancealso decreases and vice versa happens.
As there are sensitive to humidity, its resistance changes with a slight change in the surrounding
Force sensitive resistors They are also known as force sensors. When force is applied to them, its resistance changes rapidly. humidity. They are also known as resistive humidity sensors.
The resistors are important devices to the machines that we operate in our day to day activity, hence the need to have them.
Lack of one will destroy a machine due to too much current flowing through them.