It is beneficial to use resistors
Yes, it is because resistors are fundamental components in electronic circuits. It's playing very crucial role in electrotonic circuit. Resistors control the flow of electrical current.
What is a resistor?
A resistor is electrical component that control or limit the flow of electrical current in a circuit.
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Resistance is defined as the opposition to flow of current.
It is measured in ohms (Ω). Its symbol is R.
Resistance of metals is low and resistance of insulators is very high.
What are the main types of resistors?
Carbon Composition Resistor
This type of resistor is manufactured in both insulated and uninsulated form.
The construction of a moulded carbon composition
Features
These are general purpose resistors
Temperature range -55°C to 150°C
Voltage rating upto 800V
Wire Wound Resistor
The power handling capacity is higher. Metal wire are used as a material.
size is moderate we can use 2W to 20W.
Application
Zener voltage regulator
Power amplifier
Film Type Resistor
The film type resistor are classified as follow
Carbon Film Resistor
The resistive flim deposited on the glass or ceramic rod is of pure carbon.
The thickness decide value of resistor
Temperature range -55°C to 150°C
Power rating 1/8W, 1/4W, 1/2W capacity.
Metal Film Resistor
A thin film of metal or metal oxide, or metal alloy is deposited on the glass rod.
Tolerance range 0.01% to 10%
Better reliability
Long life
Better stability
Cermet resistor
Cermet is the mixture of ceramic and metal.
These resistors are used in printers, automotive, computers, cell phone and battery chargers.
Variable Resistor
Varistor
Light Dependent Resistor
Mathematical Expression
R = ρ*l/a --------------------(Equation 1)
Where
ρ = Resistivity of material and it is constant.
l = Length of the conductor
a = Cross sectional area
Factors affecting the resistance value
Temperature is not included in Equation 1 but it is one more factor that decides the value of R.
Due to change in temperature the length of conductor will change.
If temperature increases the value of Resistance also increases.
Resistors in series
Fig.1.1 Series circuit
Three resistors R1, R2 and R3 connected in series. Note that one regsistor is connected to the end of another resistor.
All the elements in series link are connected in manner this series circit called end to end cascade connection.
Fig.1.2 Equivalent Series circuit RT
All the elements connected in series circuit will carry same current I.
Expression for Equivalent resistance
RT = R1+R2+R3........................................... Eq 2
The equivalent resistance of a series circuit is equal to the sum of resistance in series.
RT = R1+R2+...................Rn ................ Eq 3
We can replace the complete series circuit by the equivalent resitance RT.
Resistors in Parallel
Parallel connection are connected across each other. That means one end of each resistor is connected to a junction Point.
The parallel combination of three resistors is connected across voltage source V.
The cureent flowing through eash resistor has a different value but the same voltage.
Expression for Equivalent resistance
1/RT = 1/R1 + 1/R2 + 1/R3
Effective resistance of two resistors in parallel
RT = R1R2/R1+R2.
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