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Resistance and Impedance differ primarily in how they react to AC and DC currents. Impedance governs the alternating Current flow whereas resistance controls the flow of AC and DC current. Difference Between Resistance and Impedance, the sort of circuit in which they operate, the elements on which they rely, their symbolic representation, real and imaginary numbers, the effect of frequency on them, phase angle, power dissipation, and energy stored are all discussed here.
| Table of Content |
Key Takeaways: Resistance, Impedance, AC Current, DC Current, Current flow, Energy, Electron, Conductor, Current
Resistance
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Resistance is introduced as a result of electron mobility in a conductor caused by the material's ionic lattice, which allows for the conversion of electrical power to heat. Electrical resistance, on the other hand, is the polar opposite of steady-state current. When a whole resistance is exposed to a DC system, it fluctuates with frequency.
Electrical Resistance
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| Rms value alternating current | LC Oscillations | NCERT Solutions for Class 12 Physics Chapter 7 Alternating Current |
Impedance
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Impedance is a term used to describe the characteristics of AC electrical circuits that are made up of capacitance and inductance. The frequency affects this figure as well. Impedance and reactance are often referred to as the same thing and are used interchangeably. It is important to remember that reactance refers to the resistance imposed on the AC diagram by capacitors and inductors, whereas impedance is the total of reactance and resistance. Impedance triangle is shown in the below diagram, which schematically defines the resistance vs. impedance term.
Relation between resistance and impedance
Any whole main circuit instrument, such as a resistor, may be represented mathematically based on its current and voltage, and we can see in the resistor instructions that the voltage within a pure ohmic resistor is exactly connected to the current flowing through it, as defined by Ohm's Law.
Resistance with Sinusoidal Supply
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An AC voltage (V) is applied to the resistor when the switch is in the Off position (R). This voltage has the ability to move the current. As the main voltage rises and falls in a sinusoidal pattern, this current will rise and fall. Because the load is a resistance, the voltage and current will both achieve their peak value or maximum and then return to zero value at the same time, i.e., they will improve and decrease concurrently and are referred to as "in-phase."
Resistance with Sinusoidal Supply
The electrical current that travels through the AC resistance then changes in sinusoidal format over time and is represented by the frequency equation I(t), where I is the maximum current value and is the phase angle coefficient. We may also show that for any specific current, such as the current passing through a resistor. So, using Ohm's Law, the peak voltage or maximum in R's terminals can be calculated as follows:
V(t) = R. I(t) = R. I.m. sin (ωt + θ)
it can be calculated by
iR(t) = IR(max) . sin(ωt)
As a result, for a given resistive system, the alternating current in the resistor varies about the applied voltage in a sinusoidal pattern. The phasors of both the current and the voltage will have the same values since the basic frequency is equal to both.
In other words, when an AC resistance is applied, there is no phase change between the voltage and current. As a result, whenever the voltage reaches its minimum, maximum, and zero values in its sinusoidal diagram, the current can reach its minimum, maximum, and zero values.
Differences Between Resistance and Impedance
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The key distinctions between resistance and impedance are briefly described below, along with a comparison chart:
| Resistance | Impedance |
|---|---|
| In an electrical diagram, resistance is employed to control the flow of current. The flow of current is determined by resistance, regardless of the current shape. | Impedance is a term that refers to a combination of inductive, resistive, and capacitive reactance. This refers to a combination of resistance and other types of reactance in various shapes and formats. |
| In both DC and AC systems, resistance is used. | Impedance is only used in AC circuits. |
| Resistance is denoted by (R). | Impedance is denoted by (I) (Z). |
| The term "resistance" refers to a numerical value consisting solely of real numbers. For instance, 5 ohms, 10 ohms, and so on. | Impedance, on the other hand, comprises both imaginary and real quantities. For example, 5R+10ij, where 10R represents the real value and 10ij represents the imaginary section. |
| Multiple resistances are simply added mathematically. This means that the total amount will be (R1+R2+R3) if three resistances are R1, R2, and R3. | To add two or more impedances, they must be added in a vectorial fashion. |
| The system's resistance value remains constant regardless of whether the frequency is DC or AC | Impedance varies with frequency. |
| Impedances have both a phase angle and a magnitude | Resistance does not have a phase shift. |
| Any substance will demonstrate power dissipation if resistances are retained in an electromagnetic field. | When the impedance is exposed to the electromagnetic system, it can store energy as well as dissipate power. |
| Resistance makes use of active power. | In impedance, the resistive section uses active power, while the inductive section uses passive power. |
Things to Remember
- Resistance and Impedance differ primarily in how they react to AC and DC currents.
- Impedance governs the alternative current flow whereas resistance controls the flow of AC and DC current.
- Electrical resistance is the polar opposite of steady-state current. When a whole resistance is exposed to a DC system, it fluctuates with frequency.
- Impedance is a term used to describe the characteristics of AC electrical circuits that are made up of capacitance and inductance. Frequency affects impedance.
- When an AC resistance is applied, there is no phase change between the voltage and current. As a result, whenever the voltage reaches its minimum, maximum, and zero values in its sinusoidal diagram, the current can reach its minimum, maximum, and zero values.
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Previous Year Questions
- A power transmission line feeds input power at 2300V to a step down transformer with its primary windings having…. [JEE Main 2018]
- An LCR circuit is equivalent to a damped pendulum. In an LCR circuit the capacitor is… [ JEE Main 2015]
- across resistance is equal to the rate at which magnetic energy is stored in the inductor is…..
- The total potential difference across the circuit is….
- The voltage developed in the secondary would be….
- The mean or average value of AC over a complete cycle is...[COMEDK UGET 2015]
- Formation of Eddy currents has desirable effects in 1...[COMEDK UGET 2008]
- As resistance in a series resonant circuit increases….[COMEDK UGET 2010]
- An inductor coil when connected to a 12V….[COMEDK UGET 2010]
- In transformer, core is made of soft iron to reduce...[UPSEE 2010]
- A coil of resistance R and inductance L is connected to….[BCECE 2010]
- A capacitor of suitable capacitance can be used in an circuit in…..[BCECE 2010]
- When an AC voltage is applied to a….[DUET 2011]
- A 20 Henry inductor coil is connected to a 10 ohm….[JEE Main 2019]
- A power transmission line feeds input power at...[JEE Main 2018]
- The total impedance, and phase difference between the voltage across the source and the current ….[JEE Main 2017]
- the series inductor needed for it to work is close to...[JEE Main 2016]
- The capacitor is then connected to an ideal inductor of self inductance...[JEE Main 2018]
Sample Questions
Ques. What is the difference between a conductor and a resistor? (2 marks)
Ans: Conductors are materials that permit electric current to pass through them. A resistor is a piece of conducting material with a specific resistance that is used in a circuit. High-conductivity materials, such as metals, such as copper and aluminium, are used as conductors. Resistors, on the other hand, are composed of a range of materials based on the intended resistance, the quantity of energy to dissipate, precision, and cost.
Ques. Is there a link between resistance and temperature? (3 marks)
Ans: Metals' resistivity normally increases as temperature rises near room temperature, whereas semiconductors' resistivity typically reduces as temperature rises. Depending on the system, the resistivity of insulators and electrolytes may rise or decrease. See Electrical resistivity and conductivity for a complete description and explanation.
As a result, wires, resistors, and other components' resistance often vary with temperature. This phenomenon could be undesirable, leading an electrical circuit to fail at high temperatures. However, in some circumstances, the effect is beneficial. When a component's temperature-dependent resistance is used for a specific purpose, the component is referred to as a resistance thermometer or thermistor. (A thermistor is constructed of ceramic or polymer, whereas a resistance thermometer is made of metal, usually platinum.)
Ques. What is the relationship between strain and resistance? (2 marks)
Ans: The resistance of a conductor is affected by strain in the same way as its resistance is affected by temperature. When a conductor is put under tension (a type of stress that causes strain in the form of stretching), the length of the tensioned part of the conductor grows while the cross-sectional area decreases. Both phenomena help to raise the resistance of the stretched conductor segment. The resistance of the stretched segment of the conductor lowers when it is compressed (strained in the opposite direction).
Ques. Define the term "superconductivity." (3 marks)
Ans: Because V = 0 and I ≠ 0 are both possible, superconductors have exactly zero resistance and infinite conductance. This also implies that there is no joule heating or electrical energy loss. As a result, if the superconductive wire is formed into a closed loop, the current will flow indefinitely around the loop. Most metallic superconductors, such as niobium-tin alloys, need cooling to temperatures in 4 K with liquid helium or cooling to temperatures near 77 K with liquid nitrogen for the pricey, brittle, and sensitive ceramic high-temperature superconductors. Nonetheless, superconductivity has a wide range of technological applications, including superconducting magnets.
Ques. Explain Ohm's law (2 marks)
Ans: The current flowing through a conductor between two places is proportional to the voltage across the conductor, according to Ohm's law. When you add the proportionality constant, resistance, to the equation, you get the following:
I= V/R
where I denote the current through the conductor in amperes, V denotes the voltage across the conductor in volts, and R is the conductor's resistance in ohms.
Ques. What exactly is Siemens? (2 marks)
Ans: In the International System of Units, the siemens (symbol: S) is the derived unit of electric conductance, electric susceptance, and electric admittance (SI). The reciprocals of resistance, reactance, and impedance are conductance, susceptance, and admittance, respectively; thus, one siemens is redundantly equivalent to the reciprocal of one ohm and is also known as the mho.
Ques. What exactly is reactance? (3 marks)
Ans: A component with a finite reactance generates a phase shift between the voltage across it and the current through it; reactance X is the imaginary part of the impedance.
The sinusoidal voltage across a purely reactive component is in quadrature with the sinusoidal current through the component, indicating that it is purely reactive. This indicates that the component receives energy from the circuit and then returns it to the circuit. There is no power dissipated by a pure reactance.
Ques. What exactly is a phasor? (2 marks)
Ans: A phasor is a constant complex integer that represents the complex amplitude (magnitude and phase) of a sinusoidal function of time. It is commonly given in the exponential form. Electrical engineers employ phasors to simplify computations involving sinusoids, frequently reducing a differential equation problem to an algebraic problem.
Ques. Is it possible for the real part of the impedance to be negative? (3 marks)
Ans: Due to the power supply's practically constant power against input voltage, the input resistance of a Switched Mode Power Supply (SMPS) is negative at DC and low frequencies.
Because the output voltage remains constant when the input voltage varies, the output power is unaffected by the input voltage. As long as the efficiency remains approximately constant as the input voltage varies, the input current must move in the opposite direction as the input voltage changes to keep the input power virtually constant.
Ques. What is the purpose of an impedance analyzer? (3 marks)
Ans: A complicated electrical impedance as a function of test frequency is measured using an impedance analyzer, which is a form of electronic test equipment.
Impedance is a critical metric for characterising electronic components, circuits, and the materials used to produce them. Impedance analysis can also be used to evaluate dielectric materials like biological tissue, foodstuffs, and geological samples.
Impedance analyzers are available in three different hardware configurations, each of which can probe from ultra-low frequency to ultra-high frequency and measure impedances from µΩ to TΩ.
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