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# Resistors

• Resistor is one of the basic component of electronic/electrical device. Its purpose is to create specified value of voltage and current.

• It provides resistance to the flow of electric current, ie. it opposes the flow of electric current.The Opposite to resistance is conductance, which does not opposes the flow of electric current as well as reduces voltage applied to the circuit.

• The rating of resistor is given in Ohms/watts, where ohms is the unit of resistor and watts means power handling capacity of resistor.If the flow of current through a resistor increases, it heats up, and if the temperature exceeds a certain critical value, it can be damaged.

• The wattage rating of a resistor is the power it can dissipate for a long period of time.The resistor is also given with value: 100R, where R stands for ohms. 1/4W, 1/2W,1W, 2W... wattage of resistors are available in market.

• The value of resistors can be measured using a device known as Multimeter.

• ## Concepts related to Resistor:

Ohms Law:

It deals with the relationship between voltage and current in an ideal conductor. It is given by V=IR. The material which deals with ohm's law are called "Ohmic" /"Linear". Hence Resistor is a Linear device.

Tolerance:

Resistors have a set value indicated by colored bands around the resistor. These bands also tells about the "tolerance" of the resistor. That means how accurate is the value of resistor. For example: a resistor with a value of 100 ohms and a tolerance of 10 percent has its value between 90 and 110 ohms.

Effect of Temperature on resistance:

The resistance due to change in temperature is know as 'temperature coefficient'. There are two types of temperature coefficients: Positive temperature coefficient and Negative temperature coefficient. When resistance increases with increase in temperature it is called Positive temperature coefficient and when resistance decreases with decrease in temperature is called Negative temperature coefficient.

## Classification of Resistors:

• Classification-1:
• They are also classified based on their temperature coefficient i.e. PTC(Positive Temperature Coefficient) or NTC(Negative Temperature Coefficient) as well as as Linear and Non-Linear Resistors.

• Classification-2:

• ## Construction of Resistors:

• Carbon Composition Resistor:

• Being a fixed type of resistor, it is made out of fine carbon particles mixed with binder material like clay and then baked to its solid form.

• Resistors of 0.25W and 0.5W, have a maximum voltage range upto 150V and 500V respectively.

• Carbon Film Resistor:

• It is fixed type resistor consists of a ceramic carrier with a thin Carbon Film around it.

• The Pitch width determines the value of resistance of that resistor. Large Pitch width results in low resistance value and small pitch width results in high resistance value.

• The range of this resistor varies between 1Ohm – 10,000 MOhms with a power rating ranging from 1/16Watt to 2Watts.

• Wire Wound Resistor:
• This type of resistors are available in both fixed and variable type.
• A wire with a high resistivity consisting of Nicel-Chromium or Manganin material is wounded on core materials like ceramic, plastic or glass.

• They have wattage ranging from few watts to 1000 Watts or greater.

• Potentiometer:

• ## Identifying Value of Resistors:

• A popular way of remembering these codes in sequence by the sentence: B. B. ROY of Great Britain has Very Good Wife. Where each capital letters in the sentence represents the colour code of resistor in sequence according to their value.

## Combinations of Resistors:

• Series:
• R(total)=R1 + R2 + R3
ex: 1K + 2K + 5K = 8K ohms

• Parallel:
• 1/R(total)= 1/R1 + 1/R2
ex: 1/1K + 1/1K = 0.5K ohms

## Applications:

• Amplifiers

• RC phase shift Oscillator

• Digital to Analog Converters

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