Basic Electrical Components ( Resistor, Capacitor and Inductor )

Basic Electrical Components

There are two types of elements found in electric circuits:

 1.  passive elements and 

2. active elements.

 An active element is capable of generating energy while a passive element is not . Examples of passive element are resistors, capacitors and inductors. Typical active elements include generators, batteries and operational amplifiers.

Resistor

A resistor is an electrical component that limits or regulates the flow of electrical current in an electronic circuit. Resistors can also be used to provide a specific voltage for an active device such as a transistor.

Fig-1: Resistor

Fig-2 : Symbol of Different types of Resistors

Resistance

The property of a substance which opposes the flow of electric current (or electricity) through it is called Resistance OR Resistance is the ability of a circuit which opposes current. Example of materials that show this property are Mica, Glass, Rubber, Wood etc. 

The unit of resistance is OHM (Ω) where 1Ω = 1V/1A.  which is derived from the basic electrical Ohm’s law = V = IR

Resistance of a resistor depends on their length (l), resistivity (ρ) and its cross sectional area (a) which is also known as laws of resistance … R = ρ (l/a) .

Types of Resistors 

Resistors are available in different size, Shapes and materials. There are two basic types of resistors.

  1.      Linear Resistors

  2.      Non Linear Resistors

   Linear Resistors

Those resistors, which values change with the applied voltage and temperature, 

  are called linear resistors. In other words, a resistor, which current value is directly proportional to

  the applied voltage is known as linear resistors.

Generally, there are two types of resistors which have linear properties.

a) Fixed Resistors
b) Variable Resistors

a)Fixed Resistors

Fixed Resistors : As the name tells everything, fixed resistor is a resistor which has a specific value and we can’t change the value of fixed resistors.

Types of Fixed resistors: 

  1.      Carbon Composition Resistors

  2.      Wire Wound Resistors

  3.      Thin Film Resistors

  4.      Thick Film Resistors

b) Variable Resistors : As the name indicates, those resistors which values can be changed through a dial, knob, and screw or manually by a proper method. In these types of resistors, there is a sliding arm, which is connected to the shaft and the value of resistance can be changed by rotating the arm.

Use of Variable Resistors :They are used in the radio receiver for volume control and tone control resistance.

Following are the further types of Variable Resistors:

1. Potentiometers 2. Rheostats 3. Trimmers

2. Non Linear Resistors : We know that, nonlinear resistors are those resistors, where the current flowing through it does not change according to Ohm’s Law but, changes with change in temperature or applied voltage.

In addition, if the flowing current through a resistor changes with change in body temperature, then these kinds of resistors are called Thermisters. 

If the flowing current through a resistor change with the applied voltages, then it is called a Varistors or VDR (Voltage Dependent Resistors).

Following are the additional types of Non Linear Resistors.

1. Thermisters 2. Varisters (VDR) 3. Photo Resistor or Photo Conductive Cell or LDR

Fig-3 : Different Types of Resistor at a glance

Uses / Application of Resistors :Practically, both types of resistors (Fixed and Variable) are generally used for the following purposes.

I. For Current control and limiting
II. To change electrical energy in the form of heat energy
III. As a shunt in Ampere meters
IV. As a multiplier in a Voltmeter
V. To control temperature
VI. To control voltage or Drop
VII. For protection purposes, e.g. Fusible Resistors
VIII. In laboratories
IX. In home electrical appliances like heater, iron, immersion rod etc.
X. Widely used in the electronics industries

Measurement the value of a resistor ( Resistance):There are two ways to measure the value of a resistor 

1.Theoretical Measurement and

2.Practical Measurement

In Theoretical Measurement, we convert the color bands that are on the resistor body. For this we also called 4 band resistor, 5 band resistor and so on. Each color is called a band and each color has a numerical code that helps us to determine the values of resistor. There are usually 12 color and each color has a value. Fig-4 shows the color, their respective code. For example for black , the code is zero (0) and for green , the code is Five (5) and so on. Normally four or Five band resistors are available in market. If we consider a four band resistor, that is 4 colors are drawn in its body, then by the following formula we can easily calculate the value of the resistor.

Resistance  ( R ) = AB×10^C ± D %

Here D is called Tolarance, which depends on the temperature.

Fig-4: Color Code

If we consider a resistor which has 4 band or color in its body and these colors are

Red, Green, Red, Gold , then the value of the following resistor will calculate as follows:

Here the respective code of the colors are

Red = 2

Green = 5

Red = 2

Gold = 5

Now if we put these values to the above formula, we get,

R = 25 × 10² ± 5 %  ohms (Ω )

R = 2500 ± 5 %  ohms (Ω )

R = (2375 – 2625 ) Ω

For Five band Resistor, the formula will be

Resistance  ( R ) = ABC×10^D ± E %

If we consider the band as Red, Green, Black, Red, Gold then,

Here the respective code of the colors are

Red = 2

Green = 5

Black = 0

Red = 2

Gold = 5

Now if we put these values to the above formula, we get,

R = 250 × 10² ± 5 %  ohms (Ω )

R = 25000± 5 %  ohms (Ω )

R= (23750 – 26250) Ω

Practical Measurement : In Practical measurement , we use a ohm meter or multimeter.

Fig-5: Measurement of  Resistance usuing Multimeter.

Characteristics of a resistor: It is very important to know about the characteristics

 any components to use it in our practical life. Fig -6 shows the circuit and characteristics curve or I-V curve of a resistor.

Fig-6: Circuit and characteristics curve of a resistor 

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All other factors being equal, in a direct-current (DC) circuit, the current through a resistor is inversely proportional to its resistance, and directly proportional to the voltage across it. This is the well-known Ohm's Law. In alternating-current (AC) circuits, this rule also applies as long as the resistor does not contain inductance or capacitance.