Electrical Resistance Explained

Capacitors store electrical energy via a dielectric, offering capacitance for filtering, smoothing, and decoupling in AC/DC circuits, RC networks, and power supplies, spanning ceramic, film, and electrolytic types with distinct impedance profiles.

What Are Capacitors?

Capacitors store charge using a dielectric, providing capacitance for filtering, timing, and decoupling in circuits.

✅ Types: ceramic, film, tantalum, electrolytic; surface-mount or through-hole

✅ Functions: decoupling, bulk energy storage, timing, AC coupling

✅ Key specs: capacitance, voltage rating, ESR/ESL, tolerance, ripple

Capacitors for Power Factor Correction

It is desirable to add shunt capacitors in the load area to supply the lagging component of current with a positive negative charging electrons. The cost is frequently justified by the value of circuit and substation capacity released and/or reduction in losses. Installed cost of shunt capacitors is usually least on primary distribution systems and in distribution substations. For foundational context, see what a capacitor is to understand reactive power roles.

The application of shunt capacitors to a distribution feeder produces a uniform voltage boost per unit of length of line, out to its point of application. Therefore, it should be located as far out on the distribution system as practical, close to the loads requiring the kilovars. There are some cases, particularly in underground distribution, where secondary capacitors are economically justified despite their higher cost per kilovar. The placement effectiveness also depends on capacitance characteristics relative to feeder impedance.

Development of low-cost switching equipment for capacitors has made it possible to correct the power factor to a high value during peak-load conditions without overcorrection during light-load periods. This makes it possible for switched capacitors to be used for supplementary voltage control. Time clocks, temperature, electric charge voltage, current flows, and kilovar controls are common actuators for high frequency capacitor switching. Utilities typically choose among several types of capacitors to balance switching duty and reliability.

Capacitor Installations

Capacitors for primary systems are available in 50- to 300-kvar single phase units suitable for pole mounting in banks of 3 to 12 units. Capacitors should be connected to the system through fuses so that a capacitor failure will not jeopardize system reliability or result in violent case rupture. When voltage ratings limit a single unit, engineers connect capacitors in series to distribute stress effectively.

Effect of Shunt Capacitors on Voltage

Proposed permanently connected capacitor applications should be checked to make sure that the voltage to some customers will not rise too high during light-load periods. Switched capacitor applications should be checked to determine that switching the capacitor bank on or off will not cause objectionable flicker in electronics. Selecting appropriate sizes in the standard unit of capacitance helps manage voltage rise and flicker.

Effect of Shunt Capacitors on Losses

The maximum loss reduction on a feeder with distributed load is obtained by locating positively negatively capacitor banks on the feeder where the capacitor kilovars is equal to twice the load kilovars beyond the point of installation. This principle holds whether one or more than one capacitor bank is applied to a feeder. To meet kvar targets with modular banks, utilities often add capacitance in parallel so reactive output scales predictably.

Capacitor kilovars up to 70% of the total kiovar load on the feeder can be applied as one bank with little sacrifice in the maximum feeder-loss discharge reduction possible with several capacitor banks.

A rule of thumb for locating a single capacitor bank on a feeder with uniformly distributed loads is that the maximum loss reduction can be obtained when the capacitor kilovars of the bank is equal to two-thirds of the kilovar load on the feeder. This bank should be located two-thirds of the distance out on the distributed feeder portion for object charging. Deviation of the capacitor bank location from the point of maximum loss reduction by as much as 10 per cent of the total feeder length does not appreciably affect the loss benefit. Therefore, in practice, in order to make the most out of the capacitor's loss reduction and voltage benefits, it is best to apply the capacitor bank just beyond the optimum loss-reduction location.

Batteries and capacitors seem similar as they both store and release electrical energy. However, there are crucial differences between them that impact their potential electronic applications due to how they function differently, depending on insulator material.

Supercapacitors

A capacitor battery aligns the molecules of a dielectric across an electric field to store energy. A supercapacitor aligns the charging of an electrolyte on either side of an insulator to store a double-layer charge.

Electrolytic capacitors consist of two or more conductive capacitors plate, separated by a dielectric. When an electric current enters the capacitor, the dielectric stops the flow and a charge builds up and is stored in an electric field between the metallic plates. Each capacitor is designed to have a particular capacitance (energy storage). When a capacitor is connected to an external circuit, a current will rapidly discharge. Plate area, separation, and dielectric constant together determine capacitance and thus energy density.

In a supercapacitor, there is no dielectric between conducting plates; rather, there is an electrolyte and a thin insulator such as cardboard or paper. When a current is introduced to the supercapacitor, ions build on either side of the insulator to generate a double layer of charge, no matter the capacitor charged. Supercapacitors are limited to low voltages, but very high capacitance frequencies, as a high voltage would break down the electrolyte. 

Batteries

There are different types of capacitor batteries, which detemine the capacitance of a capacitor. Different battery types are distinguished by their chemical makeup. The chemical unit, called the cell, contains three main parts; a positive terminal called the cathode, negative terminal called the anode, and the electrolyte. Batteries store electric energy. The battery charges and discharges through a chemical reaction that generates a voltage. The store of charge in the battery is able to provide a consistent DC voltage. In rechargeable batteries, the chemical energy that is converted into electricity can be reversed using an outside electrical energy to restore the charge of capacitors storing power in the batteries.

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The unit of electrical resistance is the ohm, symbolized by the Greek letter Ω. It measures how much a material resists the flow of electric current. One ohm equals the resistance when one volt produces a current of one ampere.

What is a unit of electrical resistance?

The unit of electrical resistance, the Ohm, is a cornerstone of the electrical world. Its importance in governing the behaviour of electric currents, designing efficient circuits, and ensuring the safe operation of devices cannot be overstated. By understanding the intricacies of resistance and Ohm's law, it is possible to harness the power of electricity to create innovative and practical solutions that benefit our daily lives.

Here’s what you need to know:

✅ Ohm (Ω) is the standard unit of electrical resistance in the International System of Units (SI).
✅ One ohm equals the resistance that allows one ampere of current to flow with a voltage of one volt.
✅ Resistance determines how easily electricity can flow through a conductor or component.

The world of electricity is complex and fascinating, with numerous components working in unison to power our lives. One such essential element is the unit of electrical resistance, the Ohm (Ω), named after Georg Simon Ohm, a German physicist. The Ohm plays a vital role in the functioning of electrical circuits and everyday devices. This article delves into the intricacies of this unit and its significance in the realm of electricity.

First and foremost, it is crucial to understand the basic concept of resistance. In simple terms, resistance is the opposition to the flow of electric current through a conductor. It is an essential factor that influences the behaviour and efficiency of electrical circuits. The Ohm (Ω) is the SI unit of electric resistance, represented by the Greek letter omega (Ω). One Ohm is defined as the resistance of a conductor that allows one ampere of current to flow when one volt of potential difference is applied across it.

Ohm's law defines the relationship between resistance, voltage, and electric current, a fundamental principle in electrical engineering. The law states that the current passing through a conductor is directly proportional to the voltage applied and inversely proportional to its resistance. Mathematically, it is expressed as V = IR, where V represents the voltage, I represents the electric current, and R represents the resistance. This equation helps in determining the resistance in various circuits and devices.

Several factors influence the resistance of a material, including its resistivity, length, cross-sectional area, and temperature. For example, materials with high resistivity, such as insulators, exhibit greater resistance than conductors, which have low resistivity. Additionally, longer conductors and those with smaller cross-sectional areas have higher resistance compared to shorter conductors and those with larger cross-sectional areas. The temperature of a material also affects its resistance, as resistance typically increases with a rise in temperature.

How do I measure electrical resistance?

You can use a multimeter, a versatile electronic measuring instrument, to measure the resistance of a component or a circuit. A multimeter can measure various electrical parameters, including voltage, current, and resistance. Follow these steps to measure the resistance of a component or circuit:

1. Turn off the power

2. Choose the right setting

3. Prepare the component or circuit

4. Connect the probes

5. Read the resistance

Interpret the results by comparing the measured resistance with the expected or specified value for the component or circuit. If there is a significant deviation, the component might be damaged, or the circuit may have a fault.

Factors such as temperature and contact resistance between the probes and the component can affect the readings when measuring resistance. Therefore, it's essential to consider these factors when interpreting the measurement results.

Resistance

Resistance plays a critical role in electrical circuits, as it regulates the flow of current and maintains the proper functioning of devices. Limiting the current flow ensures that electrical components do not overheat or become overloaded. Resistors are passive electronic components specifically designed to provide a precise amount of resistance in a circuit.

Impedance, another essential concept in electricity, is closely related to resistance. While resistance refers to the opposition of a direct current (DC), impedance encompasses both resistance and capacitance, the latter being the opposition to alternating current (AC) due to capacitive or inductive effects. Essentially, impedance is the total opposition to the flow of alternating current, combining both resistance and reactance.

The applications are vast and varied, encompassing everyday life and advanced technology. For example, resistance is integral to household appliances like electric heaters, toasters, and incandescent light bulbs, which help generate heat or light. It also plays a significant role in the design of electronic circuits and complex systems, such as computer processors.

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Electrical resistance definition explains how materials oppose current flow in circuits, measured in ohms, linked to voltage, resistivity, conductor geometry, temperature, and impedance, governed by Ohm's law and SI units in electronics.

What Is Electrical Resistance Definition?

It is the measure of how a material opposes electric current, equal to voltage divided by current and measured in ohms.

✅ Measured in ohms; per Ohm's law, resistance R equals voltage V over current I.

✅ Depends on material resistivity, length, cross-sectional area, and temperature.

✅ Key in circuit analysis, power dissipation, signal integrity, and safety.

Electrical Resistance Definition: ER occurs in an electrical circuit when current-carrying charged particles collide with fixed particles that make up the structure of the conductors. Resistance is measured in ohm. Resistance is the ohm w. Resistance occurs in every part of a circuit, including wires and especially power transmission lines. For a concise overview, see this introduction to electrical resistance to reinforce key definitions.

Dissipation of electric energy in the form of heat affects the amount of driving voltage required to produce a given current through the circuit. In fact, volts are mesured across a circuit divided by the current I (amperes) through that circuit defines quantitatively the amount of electrical resistance R. The ohm is the common unit of electrical resistance, equivalent to one volt per ampere and represented by the capital Greek letter omega, Ω. The electrical resistance of a wire is directly proportional to its length and inversely proportional to its cross-sectional area. Resistance also depends on the material of the conductor. For instance, the resistance of a conductor generally increases with increasing temperature the resistivity. This is why some conductors have almost zero resistance when cooled to extremely low temperatures, as is the case with superconductors, because of the relative resistivity of metals. There is a temperature coefficient of resistivity. If you need a refresher on potential difference and its role in circuits, review this explanation of voltage to connect the concepts.

Alternating-current resistors for current measurement require further design consideration. For example, if the resistor is to be used for current-transformer calibration, its ac resistance must be identical with its dc resistance within 1/100th% or better, and the applied voltage difference between its voltage terminals must be in phase with the current through it within a few tenths of a minute. Thin strips or tubes of resistance material are used to limit eddy currents and minimize "skin" effect, the current circuit must be arranged to have small self-inductance, and the leads from the voltage taps to the potential terminals should be arranged so that, as nearly as possible, the mutual inductance between the voltage and current circuits opposes and cancels the effect of the self-inductance of the current circuit. In (a) a metal strip has been folded into a very narrow U; in (b) the current circuit consists of coaxial tubes soldered together at one end to terminal blocks at the other end; in (c) a straight tube is used as the current circuit, and the potential leads are snugly fitting coaxial tubes soldered to the resistor tube at the desired separation and terminating at the center. These design choices are also easier to contextualize by comparing common types of resistors used for precise AC measurements.

Electrical Resistance coils consist of insulated resistance copper wire wound on a bobbin or winding form, hard-soldered at the ends to copper terminal wires. Metal tubes are widely used as winding form for dc resistors because they dissipate heat more readily than insulating bobbins, but if the resistor is to be used in ac measurements, a ceramic winding form is greatly to be preferred because it contributes less to the phase-defect angle of the resistor. The resistance wire ordinarily is folded into a narrow loop and wound bifilar onto the form to minimize inductance. This construction results in considerable associated capacitance of high-resistance coils, for which the wire is quite long, and an alternative construction is to wind the coil inductively on a thin mica or plastic card. The capacitive effect is greatly reduced, and the inductance is still quite small if the card is thin. When specifying coil assemblies, it helps to recall the standardized unit of electrical resistance so ratings and tolerances are interpreted consistently.

Resistors in which the wire forms the warp of a woven ribbon have lower time constants than either the simple bifilar- or card-wound types. Manganin is the resistance material most generally employed, but Evanohm and similar alloys are beginning to be extensively used for very high resistance coils. Enamel or silk is used to insulate the wire, and the finished coil is ordinarily coated with shellac or varnish to protect the wire from the atmosphere. Such coatings do not completely exclude moisture, and dimensional changes of insulation with humidity will result in small resistance changes, particularly in high resistances where fine wire is used. Material behavior, moisture effects, and long term stability are discussed further in this broader overview of electrical resistance for additional context.

Electrical Resistance boxes usually have two to four decades of resistance so that with reasonable precision they cover a considerable range of resistance, adjustable in small steps. For convenience of connection, terminals of the individual resistors are brought to copper blocks or studs, which are connected into the circuit by means of plugs or of dial switches using rotary laminated brushes; clean, well-fitted plugs probably have lower resistance than dial switches but are much less convenient to use. The residual inductance of decade groups of coils due to switch wiring, and the capacitance of connected but inactive coils, will probably exceed the residuals of the coils themselves, and it is to be expected that the time constant of an assembly of coils in a decade box will be considerably greater than that of the individual coils. Understanding how series and parallel combinations set the equivalent resistance will inform how decade boxes are deployed in complex networks.

Measurement of resistance is accomplished by a variety of methods, depending on the magnitude of the resistor and the accuracy required. Over the range from a few ohms to a megohm or more, an ohmmeter may be used for an accuracy of a few percent. A simple ohmmeter may consist of a milliammeter, dry cell, and resistor in a series circuit, the instrument scale being marked in resistance units, if you obey ohm law. For a better value, the voltage drop is measured across the resistor for a measured or known current through it. Here, accuracy is limited by the instrument scales unless a potentiometer is used for the current and voltage measurements. The approach is also taken in the wide variety of digital multimeters now in common use. Their manufacturers' specifications indicate a range of accuracies from a few percent to 10 ppm (0.001%) or better from the simplest to the most precise meters. Bridge methods can have the highest accuracy, both because they are null methods in which two or more ratios can be brought to equality and because the measurements can be made by comparison with accurately known standards. For two-terminal resistors, a Wheatstone bridge can be used; for four-terminal measurements, a Kelvin bridge or a current comparator bridge can be used. Bridges for either two- or four-terminal measurements also may be based on resistive dividers. Because of their extremely high input impedance, digital voltmeters that be used with standard resistors in unbalanced bridge circuits of high accuracy. For quick reference during test planning, the fundamental resistance formula clarifies how R, V, and I are related under Ohm law.

Digital multi meters are frequently used to make low-power measurements of resistors in the range between a few ohms and a hundred megohms or so. Resolution of such instruments varies from 1% of full scale to a part per million of full scale. These meters generally use a constant-current source with a known current controlled by comparing the voltage drop on an internal "standard" resistor to the EMF produced by a Zener diode. The current is set at such a level as to make the meter direct-reading in terms of the displayed voltage; that is, the number displayed by the meter reflects the voltage drop across the resistor, but the decimal point is moved and the scale descriptor is displayed as appropriate. Multimeters typically use three or more fixed currents and several voltage ranges to produce seven or more decade ranges with the full-scale reading from 1.4 to 3.9 times the range. For example, on the 1000-0 range, full scale may be 3,999.999 Q. Power dissipated in the measured resistor generally does not exceed 30 mW and reaches that level only in the lowest ranges where resistors are usually designed to handle many times that power. The most accurate multimeters have a resolution of 1 to 10 ppm of range on all ranges above the 10-0 range. Their sensitivity, linearity, and short-term stability make it possible to compare nominally equal resistors by substitution with an uncertainty 2 to 3 times the least count of the meter. This permits their use in making very accurate measurements, up to 10 ppm, or resistors whose values are close to those of standards at hand. Many less expensive multimeters have only two leads or terminals to use to make measurements. In those cases, the leads from the meter to the resistor to be measured become part of the measured

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Understanding the short circuit definition and associated risks is crucial for ensuring electrical safety in homes and workplaces. By knowing the common causes of short circuits and employing preventive measures such as regular inspections, proper installation, and protective devices like circuit breakers and GFCIs, we can minimize the dangers associated with short circuits and create a safer environment for everyone.

A short circuit phenomenon occurs in electrical circuits and poses potential safety hazards. To better understand the short circuit definition, one must first become familiar with the fundamentals of electrical circuits. An electrical circuit is a closed loop through which electrical current flows, and it consists of various components such as power sources, conductors, and electrical devices. A short circuit happens when an unintended, low-resistance path is formed within the circuit, causing a significant increase in current flow.

What are the different types of short circuit?

There are three main types of short circuits, each with unique characteristics and implications. These types are categorized based on the specific components of the short circuit within an electrical system. Here are the three types of short circuits:

Phase-to-Phase

This type of short circuit, also known as a line-to-line short circuit, occurs when two or more phases of an electrical system come into contact with each other. For example, this can happen when insulation between the phases is damaged or worn out, or due to a fault in the equipment or wiring. A phase-to-phase short circuit rapidly increases current flow between the affected phases, which can cause significant damage to the electrical system and generate considerable heat.

Phase-to-Neutral

A phase-to-neutral short circuit, sometimes called a line-to-neutral short circuit, occurs when a live conductor (phase) comes into contact with the neutral conductor. This can occur due to damaged insulation, loose connections, or faulty equipment. In a phase-to-neutral short circuit, the current flows between the affected phase and the neutral conductor, resulting in an increased current flow and potential damage to the electrical system.

Phase-to-Ground

This type of short circuit, also known as a ground fault, occurs when a live conductor (phase) comes into contact with a grounded object or the earth. For example, this can happen when insulation is compromised, equipment is faulty, or wiring is damaged. A phase-to-ground short circuit results in a sudden surge of current as electricity takes the path of least resistance through the ground, posing a risk of damage to electrical components, fire, and electrical shock.

Each of these types can cause significant harm to electrical systems and pose potential safety hazards. Therefore, maintaining proper insulation and connections within electrical systems and implementing protective devices such as circuit breakers and ground fault circuit interrupters (GFCIs) is crucial to minimize the risks. In addition, regular inspections and maintenance of electrical equipment are also essential in ensuring the safe operation of electrical systems.

Now that we've laid the groundwork, let's delve deeper into the definition. A short circuit is defined as an abnormal connection between two nodes in an electrical circuit, allowing an excessive amount of current to flow through a low-resistance path. This can lead to various problems, including damage to electrical components, increased risk of fire, and even electrical shock.

So, how do short circuits occur? Several common causes include damaged or frayed electrical wires, improper connections, or faulty insulation. In addition, when conductive materials come into contact, they can create an unintended path for electrical current. This leads to a significant increase in current flow, resulting in a short circuit.

The dangers associated with short circuits cannot be overstated. When a short circuit occurs, it can generate intense heat, which poses a significant fire risk. Additionally, the increased current can cause conductor failure and damage to electrical components, leading to malfunctions and even total system failure. Furthermore, if an individual comes into contact with a short-circuited component, they could suffer from electrical shock, which can sometimes be fatal.

Preventing short circuits is a vital aspect of maintaining electrical safety. One of the most effective prevention methods is ensuring proper installation and maintenance of electrical systems. In addition, regular inspections should be conducted to identify and repair damaged wiring or faulty connections. Installing overload protection devices, such as circuit breakers or fuses, can also help protect against short circuits. These devices are designed to detect and interrupt the excessive current flow, thus mitigating the risk of damage or injury.

Circuit breakers play a crucial role in safeguarding electrical systems from the effects of short circuits. These devices are engineered to detect an unusually high current flow, which could indicate a short circuit or another fault. Once detected, the circuit breaker will automatically interrupt the current flow, isolating the affected section of the circuit and preventing further damage or injury.

To further understand short circuits, it's important to distinguish them from ground faults. While both phenomena involve an abnormal connection within an electrical circuit, a ground fault is a specific type of short circuit that occurs when a live conductor comes into contact with a grounded object or the earth. This can lead to a sudden current surge and pose similar risks, such as fire and electrical shock. However, ground faults can be detected and mitigated using specialized devices called ground fault circuit interrupters (GFCIs).

Remember, always be vigilant when dealing with electrical systems. If you are uncertain about a potential issue or unsure how to handle a situation, consult a licensed electrician for assistance. Electrical safety is everyone's responsibility, and understanding definition is a fundamental step in preventing accidents and promoting a safe environment.

Active power is the actual energy consumed by electrical equipment to perform useful work, such as lighting or running motors. It is measured in kilowatts (kW) and is essential for efficient power system design, load management, and energy billing accuracy.

What is "active power"?

Active power is the real power consumed in an AC circuit to perform useful work.

✅ Measured in kilowatts (kW)

✅ Powers resistive loads like heaters, lights, and motors

✅ Crucial for calculating energy usage and efficiency

In AC circuits, active power (P) refers to the component of electrical power that results in energy transfer to a load. It is the energy that performs work—such as producing motion, light, or heat—and is distinct from reactive power, which oscillates between source and load without being consumed.

Active Power Formula

The general formula for active power is:

P = VIcosθ

Where:

• P = Active Power (watts)

• V = RMS Voltage

• I = RMS Current

• θ = Phase angle between voltage and current

In real-world power systems, only the portion of the current in phase with the voltage contributes to active power. The portion out of phase results in reactive power and does not produce usable energy.

Equation 1

The above active power equation is valid for both sinusoidal and nonsinusoidal conditions. For sinusoidal condition, '1rn, resolves to the familiar form,

Equation 2

Sinusoidal and Non-Sinusoidal Conditions

The calculation of active power can differ slightly depending on waveform distortion:

• For sinusoidal conditions, Equation 1 simplifies to the standard P = VIcosθ form.

• For non-sinusoidal waveforms, the total active power includes the sum of contributions from all harmonic components. However, since voltage distortion is typically below 5% in most power systems, the simplified equation is usually accurate enough for practical purposes.

Real-World Example

A standard incandescent light bulb converts electrical power into visible light and heat. This is a classic case of active power at work—where the current and voltage are in phase, and virtually all supplied power is consumed usefully.

Active vs Reactive vs Apparent Power

It’s important to distinguish active power from related concepts:

• Reactive Power (Q): Energy exchanged but not consumed, measured in kVAR.

• Apparent Power (S): The vector sum of active and reactive power, measured in kVA.

• Power Factor: The ratio of active power to apparent power (PF = P/S).

While active power does the real work, apparent power impacts system loading and reactive power affects voltage stability. See our power factor training for more.

Measurement and Application

Active power is typically measured using true RMS meters that calculate the average of the instantaneous product of voltage and current. Advanced power analyzers now offer direct measurement of real power in both clean and distorted systems.

Engineers use active power data for:

• Energy consumption analysis

• Load management and optimization

• System efficiency evaluation

• Compliance with energy standards

Related Reading

• Understand the difference between active and reactive power

• Learn how to improve system performance with our power quality analysis training

• Discover how electrical resistance affects power consumption

• Explore the role of power factor correction in reducing energy waste

Frequently Asked Questions

What is active power used for?

Active power is used to perform real work in electrical systems, such as lighting, heating, and running motors.

Is active power the same as real power?

Yes. Active power, real power, and true power are interchangeable terms that refer to the same concept.

How is active power calculated?

It is calculated using the formula P = VIcosθ, where V and I are RMS voltage and current, and θ is the phase angle between them.

In summary, understanding active power is essential for designing efficient electrical systems and ensuring energy accountability. By distinguishing it from reactive and apparent power, professionals can improve system performance and reduce energy losses.

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Thevenin’s Theorem simplifies complex linear circuits into a single voltage source and series resistance, making circuit analysis easier for engineers. It helps calculate current, load behavior, and equivalent resistance in practical electrical systems.

What is Thevenin’s Theorem?

Thevenin’s Theorem is a method in circuit analysis that reduces any linear electrical network to an equivalent circuit with a voltage source (Vth) in series with a resistance (Rth).

✅ Simplifies circuit analysis for engineers and students

✅ Calculates load current and voltage with accuracy

✅ Models equivalent resistance for real-world applications