What is Resistance?
Resistance to electricity, also known as electrical resistance, is a force that opposes the flow of current. In this way, it indicates how difficult it is for current to flow.
The unit of measurement for resistance is ohms (Ω).
When there is an electron differential between two terminals, electricity flows from high to low. That flow is countered by resistance. The lower the current, the greater the resistance. In contrast, the greater the current, the lower the resistance.
What are resistors?
Resistors are electronic components that prevent electricity from flowing through a circuit. In electric circuits, resistors are used to adjust current and voltage in the same way that faucets are used to adjust the flow of tap water. They can be used to not only control current flow, but also to distribute voltage in a circuit.
Resistors are classified into several types, the most common of which are as follows:
- Fixed resistors
- Variable resistors
- Potentiometers
Working principle of resistors
A conductor is a material that allows electricity to flow easily through it. The insulator is the polar opposite of a conductor in that it does not allow current to flow easily through it.
The difficulty with current flow properties is a direct result of resistance – conductors, such as copper, have a low resistance to the flow of electric current, whereas insulators resist the flow of electric current to a great extent, i.e., have a high resistance.
When electrons flow through a wire, some of them pass easily through the gaps, while others hit an atom and bounce, and occasionally electrons collide; this causes the flow of electrons to be somewhat non-uniform and impeded (slow current flow rate) – this is resistance.
This also implies that resistance is affected by the type and properties of the material itself, because the interaction of electrons with atoms is affected by the size and packing of the atoms.
What is Impedance?
Impedance is the sum of resistance and reactance. It is defined as anything that obstructs the flow of electrons within an electrical circuit. As a result, it has an effect on the generation of current through the electrical circuit. It can be found in all possible circuit components and across all possible electrical circuits. Impedance is represented mathematically by the letter Z, and its unit is the ohm.
Formula
Resistance
Resistance of a circuit can be calculated by the value of voltage and current in the circuit.
Resistance = Voltage / Current
Ohm’s law is the name given to this formula. If the voltage remains constant, the resistance value decreases as the current–the denominator–increases. In contrast, as the current decreases, the resistance value increases. In other words, resistance is low in large current circuits and high in small current circuits.
Impedance
In phasor terms, impedance Z is denoted as the resistance R and reactance X combination:
X = R + j X
Where reactance X is the sum of Inductive XL and capacitive Xc
X = XL + Xc
Impedance: Z = R or XL or XC (if only one is present)
Impedance in series only:Z = √(R2 + X2) (when both R and one type of X are present)
Impedance in series only: Z = √(R2 + (|XL - XC|)2) (when R, XC, and XL are present)
Impedance in any circuit:Z = R + jX (j is the imaginary number √(-1))
Resistance Vs Impedance
| S. No | Resistance | Impedance |
|---|---|---|
| 1 | Resistance is the capacity to withstand the flow of current | Impedance is a term that refers to a combination of resistance, inductive reactance, and capacitive reactance. |
| 2 | Resistance is denoted by R | Impedance is denoted by the symbol R |
| 3 | Resistance occurs in both AC and DC circuit | Impedance only occurs in AC circuit |
| 4 | Resistance does not have any phase angle. | Impedance has both magnitude and phase angle. |
| 5 | Resistance value always real like 7.5Ω, 15Ω | Impedance value is complex quantity |
| 6 | Active power is consumed by resistance. | The resistive part of impedance consumes active power, while the inductive part consumes reactive power. Capacitor, on the other hand, is regarded as a reactive power generator. |
| 7 | No operator is required to represent resistance. It is just written as scalar. | Impedance is represented by an operator known as the “j” operator. When multiplied by any vector, this “j” operator rotates it by 90 degrees in an anti-clockwise direction. |
| 8 | If kept in an electromagnetic field, it only represents power dissipation in any material. | If we placed in an electromagnetic field, it signifies both power dissipation and energy stored. |
| 9 | It is the circuit’s contribution from the resistive element. | It is the sum of both resistance and reactance. |
| 10 | Ohmmeter is used to find resistance value | Impedance analyser is used to measure Impedance |
| 11 | The electrical power is dissipated in the form of heat. | The electrical power is dissipated and stored. |
Application of Resistance in circuits
The applications of resistance are
We can adjust the resistance value by using knob. We can control the motor speed, loudness of amplifier etc.
When some components require a much lower voltage than the supplied input voltage, dividing the voltage (the potential difference) works. Connecting the resistors in series will help to equalise the voltage drop across each resistor, allowing the appliances to operate more smoothly in those conditions.
Application of Impedance in circuits
Impedance is used to manage or control the current flow in a circuit by adjusting the value of capacitors.
Some Useful Questions
1 . How to calculate Resistance from Impedance?
When using resistors in AC circuits, the term Impedance with the symbol Z is commonly used to denote their resistance. As a result, we can say that DC resistance = AC impedance, or R = Z, for a resistor.