resistors - electrical engineering

An absolute guide from ABC to XYZ.

Resistor

a) An electrical component which provides resistance to current flow

b) Most commonly used electrical component

What is Resistor

Resistance

• It is the ability of resistor to oppose flow of current

• It is Measured in unit ‘Ohms’ and denoted by unit Ω

• Different prefixes are used to represent Resistance

• Three most commonly used prefixes are:

Resistance Prefix

1000 1k

1,000,000 1M

1,000,000,000 1G

Symbols

1. Internationally a zig-zag model is used to represent the resistors.2. Whereas in UK most people use the symbol on left.

Types of Fixed Resistors ( Design Models)

Carbon film Metal film Metal Oxide

Wire wound resistors

Types of Resistors

PotentiometerIt provides variable resistance.

Phototransistor Tapped Resistor

• These are inexpensive and are very easily available resistors.

• These resistors are available in Ranges 1Ω to 100 MΩ

• The power ratings are in between 0.125-2W.

Cons

• There is a large tolerance in rating and mostly 5-10% difference is expected.

• Such resistors are recommended for small applications like experiments in labs. But are not recommended for large applications.

Carbon Film Resistors

• They re expensive compared to Carbon Film resistors

• Are highly recommended for projects

Metal Film Resistors

• They have special ability to dissipate large quantities of heat.

• These are recommended when there is large variation in temperatures.

• Such resistors contain porcelain which is covered by metal (usually steel or some kind of mixed steel alloy).

• This steel alloy is then again coated with porcelain

• Remember that porcelain has property to absorb heat through conductors.

Wire wound resistors

• Such resistors are enclosed in IC’s

• They are expensive as compared to single resistor but are quite easy to manage.

• Can be used where you require 4 or more resistors and less space is available

Integrated Resistors

• They provide variable resistance.

• Are required when you need variable values, for example you may need 7k ohm.

• Have large values of applications in motor speed control, fan speed control, radio frequecnies.

Variable Resistor (Potentiometer)

Symbol

Practical LookWorking

• Its resistance depends on the temperature

• If temperature changes the value of resistance changes.

Thermistor

How it looksSymbol

• NTC stands for negative temperature coefficient.

• The resistance of such resistors decreases with increase in temperature.

• Such resistors are installed in parallel

NTC Thermistor (Continue)

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Temperature along x-axis

• PTC stands for positive temperature coefficient

• The resistor of such components increases with temperature

• They are mostly loaded in parallel

PTC Thermistor Continue

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Temperature along x-axis

• Used to identify the values of resistors.

• A color code chart is used for reference.

Resistor Color coding

• Resistors in circuits can be arranged in three configurations

1.Series

2.Parallel

3.Series-Parallel

Resistor configurations

• Two or more components are in series if the head of one connects with tail of another.

• Image below displays three resistors that join in series to each other.

Series Configuration

• In Numerical analysis you are mostly required to solve all resistors to simple single resistor.

• To solve resistors in series simply add them:

Series Configuration (continue)

• Two resistors are in parallel when their heads and tails are joined together.

Parallel Configuration

• To solve parallel resistors the formula used is:

Parallel Resistors (Continue)

• Very often complex circuit contain series-parallel configurations.

• However you can easily solve them if you learn the basic concept.

Series-Parallel

• You need a ohmmeter to measure it practically.

• Connect Ohmmeter in parallel to the resistor and it will display the value.

How to measure Resistance???

• In numerical problems you can find the resistance provided voltage and current is given.

• Use Ohm Law for this purpose.

R = V/I

Resistors & Ohm Law

• Guzel Sansilaniz is an Electrical Educationist, Design Engineer (Siemens) , Part time teacher (working in a school (voluntarily) too), student (wow).

• I am learning and I will share all I learn,

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