In this informative article, we will delve into the world of Resistors and their wide-ranging applications. By focusing on the following key aspects, we aim to provide you with a comprehensive understanding of resistors:

• What is Resistor?
• Mathematical Relations
• Electronic Symbols
• How to connect resistors in a circuit?
• Application of resistors in a circuit

What is a resistor?

Let’s start by answering the fundamental question: What is a resistor? The resistor is an electronic component that limits the flow of current in the circuit.  A resistor plays a crucial role in controlling the flow of current within a circuit, it accomplishes this by introducing resistance, measured in ohms, which hinders the flow of electrical current. By varying the resistance, resistors allow us to regulate current levels and protect sensitive components. The symbol for an ohm is the Greek capital omega: Ω. 1000Ω = 1KΩ (1 kilo Ω)  and 1000000Ω = 1MΩ (1 mega Ω)

Mathematical Relations of a Resistor

Mathematical relations govern the behaviour of resistors in circuits. When resistors are connected in series, their total resistance can be calculated by adding the individual resistances: R = R1 + R2 + Rn. Conversely, when resistors are connected in parallel, the reciprocal of the total resistance is equal to the sum of the reciprocals of the individual resistances: 1/R = 1/R1 + 1/R2 + 1/R3 + 1/Rn. These relations aid in determining the overall resistance in various circuit configurations.

Resistances in series    R = R1 + R2 + Rn
Resistances in parallel  1/R = 1/R1 + 1/R2 + 1/R3 + 1/Rn
Voltage drop             V = IR where I is current
Power dissipation        P = I^2R = V2/R

Electronic Symbol of  Resistors

There are two symbols for the resistor, zigzag lines, and a rectangular box. Either of these two symbols is accepted to represent Resistor.

Variable Resistor

Symbol for Rheostat

The symbol for a voltage-dependent resistor (Varistor)

The symbol for negative temperature coefficient (NTC) resistor (thermistor)

The symbol for the Heating Element resistor

 

Symbols for Light Dependent Resistor (LDR)

How to connect resistors in a circuit?

Resistors connected in series

Resistors connected in parallel

 

Applications of resistors in a circuit

Application of  Resistor as a Current Limiter:

Placement of the correct value of a resistor in series with Transistors, LEDs and other semiconductor components in a circuit limit the amount of current to what they need to function without damage.

Application of Resistor as a Voltage Divider:

Resistors are connected; one after the other, to form a series circuit, and voltage ratios will be obtained across each of them. If the resistors are the same value, the voltage drop across each will be equal; otherwise, it would be proportional to the resistance of each resistor. Voltage dividers are helpful for components that need to operate at a lesser voltage than that supplied.

Application of Resistor as a Timer and Frequency generator:

A good timing source can be obtained by connecting the resistor to a capacitor. Such a combination can be found in

1. Light flashers
2. Electronic sirens
3. And many other circuits depend on this feature to generate a pulse.

Application of Resistor  in Controlling Volume, Light intensity and Motor Speed:

Variable Resistors allow the setting of resistance by sliding a slider or turning a knob. And varying the resistance allows us to change the amount of current flowing in a circuit. Variable resistors are used to control the loudness of an amplifier, the pitch of a musical tone, the speed of a motor and light intensity.

Resistors can also be used as:

1. Shunts in ammeters and voltage meters
2. Damping agents in oscillators
3. Feedback networks in amplifiers
4. Pull-up for input-output line
5. Pull-down for input-output line 

Applications of Thermistors include:

1. Measurement and control of temperatures
2. Time delay
3. Temperature compensation
4. Liquid level indicators.

Applications of Varistor include:

1. Voltage surge
2. Protective circuits
3. Generation of non-sinusoidal waveform

 

Connection of resistor in a circuit