Convert kiloohm [kΩ] to ohm [Ω] • Electrical Resistance Converter • Electrical Engineering • Compact Calculator • Online Unit Converters (2024)

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Overview

We can say that the term “resistance” is more “lucky” than many other terms in physics, because we are used to this word and its meaning from early childhood. When we are small, we explore our environment and learn about various types of resistance, not only in the electrical sense. For example, we face resistance of the other child, whose toy we try to borrow. Electrical resistance usually does not cause bewilderment or misunderstanding when we study it at school.

It is used so much in today’s world, that we cannot even count all of the resistors — devices that operate based on resistance. It is enough to mention that in the most common electronics used today — mobile phones, smartphones, tablets, and computers — the number of resistors can reach several hundred thousand. Statistically, more than 35% of electronic components on circuit boards are resistors. Given the amount of production of such devices globally, we can estimate that there are tens of trillions of them. We could say that along with the other passive electronic components such as inductors and capacitors, resistors are part of the foundation of our civilization as we know — they are the metaphorical whales that our world rests on.

Definition of Electrical Resistance

Electrical resistance is a physical quality of matter to resist the loss-free flow of an electric current through it. In electrical engineering, resistance is a property of an electrical circuit or its part, which prevents electric current from flowing freely through it. It is calculated as a ratio of the potential difference (voltage) between two points of the circuit to the current that runs through the circuit.

Electrical resistance is related to the transport and conversion of electrical energy to other types of energy. When the conversion from electrical energy to thermal energy is irreversible, we talk about resistance. On the other hand, when the electrical energy is reversibly converted into energy of a magnetic or an electric field, and if the alternating current runs through the circuit, we consider electrical reactance. If there is a large amount of inductance in the circuit, then we consider inductive reactance, and if there is capacitance, then we talk about capacitive reactance. When we say “resistance” we could mean a specific case in the example with thermal energy above, or we could talk about resistance and resistivity in general.

When we want to make sure to include both in our discussion of the behavior of circuits with alternating current, we talk about electrical impedance, which combines the specific case of resistance discussed above and capacitive and inductive reactance. When we discuss electromagnetic fields and electromagnetic waves, then we talk about wave impedance.

Ohm’s Law

Resistance can be denoted by the letter R or r, and is considered a constant for a given conductor within specific limits. It can be found as:

R = U/I

Where

R is resistance measured in ohms (Ω);

U is the potential difference or voltage between the ends of the conductor, measured in volts (V);

I is the electric current that runs between the ends of the conductor, measured in amperes (A).

This formula is known as Ohm’s law, named after the German physicist who discovered it. There is another important law that describes the discharge of heat energy when an electric current passes through a conductor. This law is known as Joule’s first law:

Q = I² × R × t

where

Q is the amount of heat discharged during a given time t, where the energy is measured in joules (J);

I is the electric current (A).

R is resistance (Ω);

t is the duration of time during which the current is running through the conductor, measured in seconds (s).

Units

Ohm and values derived from it such as kiloohms (kΩ) and megaohms or megohms (MΩ) are the SI units used to measure resistance. You can see how ohms relate to other units by using the unit converter on our website.

Some History

Georg Simon Ohm was an outstanding physicist, among the first to research electrical resistance. In one of his works published in 1827, he stated the famous law named after him that describes the relationship between the potential difference, electric current, and resistance. This discovery had a tremendous impact on the research of electricity and on the development of methods to use it in daily life and in the industry. Unfortunately, in the beginning, his contemporaries did not grasp the importance of his work, and he was, in fact, made to resign from his post of a mathematics teacher in Cologne for publishing the results of his work in the local papers. He was finally recognized for his contributions to physics when he was awarded the Copley Medal on the 30th of November, 1841 by the Royal Society of London. In 1881 it was suggested during the International Exposition of Electricity in Paris that the unit of electrical resistance is named after him.

The Physics of Resistance in Metals and Uses for It

All of the materials are divided according to their relative resistance into conductors, semiconductors, and dielectrics. There is also a special separate class for materials, the resistance of which is zero or near to zero. They are called superconductors. Some of the most common examples of conductors are metals, although their resistance can be within a rather wide range, depending on the properties of their crystal lattice.

Currently, we think that atoms of metals form a crystal lattice. Valence electrons form the so-called “electron gas” traveling through the lattice.

The relatively low resistance of metals has to do with their composition — they have as part of their structure a large number of conductivity electrons, which are charge carriers for the atoms that the material is composed of. An external electric field causes the electrons to move in a systematic way, and this motion causes an electric current to flow through the material. The electric field accelerates the electrons, and they then collide with the ions of the crystal lattice. These collisions change the momentum of the electrons. As a result, they lose some of their kinetic energy, because it is converted into the energy stored in the crystal lattice. This stored energy causes the conductor to warm up as the electric current runs through it. It is important to note that the resistance of a given metal or an alloy depends on its geometry and does not depend on the direction of the external electric field that is applied to this material.

As this external field intensifies, the electric current that runs through the metal increases, and more and more heat is emitted. This heat may increase so much that it will melt the metal. Fuses that have a wire component use this property. The wire melts if the heat exceeds the pre-set standards, as determined by the melting point of the material chosen for the wire. The melted wire interrupts the current flow in the electric circuit. We can get an idea of what happens to fuses in action if we look at photographs or videos of filament failure in an incandescent light bulb.

The most common use for electrical resistance is its use as a heating unit. We use this property while cooking and heating food on electrical stoves, baking bread and cakes in electrical ovens, and also when working with electric kettles, coffee makers, washing machines, and electric irons. We rarely acknowledge this in our everyday life, but we owe our comfort to electrical resistance, whether we turn on the water heater for our shower, an electric fireplace, or an air conditioner with a heater function to heat our room. All of these devices have a heating element that uses electrical resistance.

Electrical resistance is used in the industry for drying when creating processed foods, to facilitate ideal temperatures for chemical reactions when making medicine, plastic bags, or for creating products from plastics using the process of extrusion.

The Physics of Resistance in Semiconductors and Uses for It

Unlike the case with metals, the crystalline structure of semiconductors is formed due to covalent bonds between atoms of the semiconductor. Because of this, semiconductors in their pure form without other materials mixed into them have a higher electrical resistance than do metals. We should note that when talking about semiconductors we usually consider their intrinsic conductivity, not their resistance.

When we mix the semiconductor material with another material that has atoms with a larger number of electrons on the outer electron shell, the semiconductor becomes n-type because of the extrinsic conductivity. This is known as doping. In fact, semiconductors of this type along with the p-type ones are known as extrinsic semiconductors. In this case, the “extra” electrons become part of the total group of atoms in a given semiconductor, and its resistance decreases. Similarly, when we add other atoms to the semiconductor that have fewer electrons on the outer electron shell, we get a p-type semiconductor. Here the “missing” electrons, known as “holes”, become part of the whole group of atoms in the semiconductor, and the semiconductor’s resistance also decreases.

In the most interesting case parts of the semiconductor have mixed conductance as a result of having two types of materials joined together. This is known as a p-n junction — it has a unique property known as anisotropy, which is characterized by the semiconductor’s dependence on the external electric field. The resistance of the p-n junction depends on the direction of this external electric field. When the voltage “locks” this type of semiconductor, the intermediate boundary layer connects the two types of conducting material and the overall resistance drastically increases. When the voltage “unlocks” the intermediate layer, the recombination of carriers occurs in the intermediate layer, and the resistance of this p-n junction rapidly increases.

Rectifier diodes, which are some of the key electronic components, operate on this principle. Unfortunately, when the electric current that runs through the p-n junction exceeds the allowed value, a thermal breakdown occurs. This causes both the p-type and the n-type elements to move through the p-n junction, and the device fails.

The main thing we should keep in mind about the p-n junction is that its resistance is not linear but depends on the direction of the external electric field, which is to say that its properties are not in accordance with Ohm’s law.

The processes that happen inside MOSFET (metal-oxide-semiconductor field-effect) transistors are different. The electric field controls their source and drain resistance. The polarity created by the gate depends on whether it is the p-type or the n-type channel. MOSFET transistors are used almost exclusively in the on-off mode — they represent the majority of electric components in modern digital devices.

Regardless of their performance, we can say that to a certain degree all transistors are in fact inertialess controlled electrical resistors.

The Physics of Resistance in Gases and Uses for It

Under normal conditions, gases are great dielectrics because they have a very small number of charge carriers such as positively charged ions and electrons. This property of gases is used in contact switches, overhead power lines, and air-gap capacitors because air is a mix of gases and its electric resistance is very large.

Gases have ionic conductance, and because of it when an external electric field is acting upon the gases, their resistance slowly decreases. This is a result of the increase in the ionization of molecules. As the voltage increases, a glow discharge occurs and the resistance becomes more closely dependent on the voltage. This property of gases was used in the past in gas lights called stabistors for stabilizing the DC for a wide range of currents. As the external voltage further increases, the discharge in the gas becomes a corona discharge, the resistance drops more, and the discharge turns into an electric spark. As this happens, an equivalent of a small lightning occurs and the resistance of the gas around the lightning drops to a minimum.

The property of ionized gases to glow when a small electric current flows through them is widely used in neon lighting for advertising, for displaying the electromagnetic field (neon voltage testers), and in sodium-vapor lamps used for lightning. Energy-saving compact fluorescent lamps work on the same principle due to the ability of mercury vapors to glow in the ultraviolet spectrum. The light of the visible spectrum is produced by the conversion of the ultraviolet radiation into visible light in a phosphor coating, which covers the inside of the lamp. Similar to semiconductors, the resistance of gases is non-linear and depends on the external electric field. It also does not comply with Ohm’s law.

The Physics of Resistance in Electrolytes and Uses for It

Electrolytes are liquids that conduct electricity. Their resistance is determined by the concentration of ions of different polarities. These ions are atoms or molecules that either lost or gained electrons. In the former case they are called cations, and in the latter case — anions. When we place two electrodes with opposite charge inside an electrolyte and thus create an external electric field, cations and anions start moving. The mechanism of this process is based on the charging and the loss of charge of a given electrode. Anions give away extra electrons on the anode, and cations gain the missing electrons on the cathode.

A significant difference between electrolytes and metals, semiconductors, and gases is the movement of particles of the electrolytes within them. It is widely used in medicine and technology, from refining metals by filtering out impurities to the introduction of medicine into a given area of the body through electrophoresis. We owe our shiny bathtubs and faucets to electroplating — a process of covering surfaces with metals, chrome, and nickel in this case. The quality of electroplating depends on the temperature and resistance of the electrolyte, in which the process runs, as well as on other parameters.

From the perspective of physics, our body is an electrolyte and we have to remember it when it comes to personal safety, in particular with regards to resistance and the electric current running through the body. The average resistance of human skin is about 50 kΩ, equivalent to a weak electrolyte, but it can change depending on the emotional state of the person and on the environment, as well as on the area of the contact between the conductor and the skin. Stress, agitation, and uncomfortable conditions can cause resistance to decrease, and because of this, it is common to assume the resistance of 1 kΩ when considering safety.

We should note that the lie detector works by measuring the resistance on different areas of the skin. It is believed to aid with determining which questions are uncomfortable for the interviewee when used in conjunction with other physiological measurements. We should keep in mind that this method is very limited — it gives incorrect readings when used with psychologically unstable people, with those trained on “cheating” this device, and with people who have an unusually high skin resistance.

Ohm’s law can be applied to electrolytes to a degree, but after a certain threshold for the strength of the external electric field is reached, the resistance of the electrolyte becomes non-linear.

The Physics of Resistance in Dielectrics and Uses for It

The resistance of dielectrics is rather high, and this property is widely used in physics and engineering when using these materials as insulators. The vacuum is the ideal dielectric. What resistance could we possibly talk about in a vacuum? Well, thanks to one of the less popular works of Albert Einstein (compared to his famous work on relativity), the one that considers the work performed by electrons separating from a metal, using resistance in a vacuum, we can now create a number of electronic devices that have been serving mankind since the early days of electrical and RF engineering.

According to Einstein, any conducting material is surrounded by a cloud of electrons, which creates a cathode ray when an electric field is applied to them. Two-electrode vacuum devices have different resistance when the polarity of the applied voltage changes. Until the 1960s, they were used for the rectification of alternating current. Vacuum tubes with three or more electrodes were used to amplify signals. Now they are replaced by more energy-efficient transistors.

However, vacuum tubes are still used in the industry. X-ray tubes and magnetrons that are used in radars are vacuum tubes. In order to understand the physical processes, engineers still use the screens of oscilloscopes made with cathode ray tubes, doctors cannot do without x-rays, and all of us use microwave ovens, in which magnetrons produce microwave radiation used to heat food.

Because the nature of conductance in a vacuum is electronic, the resistance of most vacuum tube devices abides by Ohm’s law.

Resistors and Their Use

A resistor is a passive component that is used to provide electrical resistance in electrical circuits. In addition to resistance, resistors, as a technical manifestation of the phenomenon of electrical resistance, have small capacitance called stray capacitance and small inductance called stray inductance. In practical applications, engineers often consider the non-linearity of the current-voltage characteristic of resistors.

A resistor is a device needed in every electrical circuit. According to the statistics, they make up to 35% of any circuit. Of course, we could make a circuit without them, but this would simply be a theoretical entity — practical implementations are unimaginable without resistors. An electrical engineer could call any electronic component a resistor, regardless of how it was made and designed, as long as it provides electrical resistance. A great example of this is the crash of the airship of the researcher Umberto Nobile, named “Italy”. The radio operator managed to send out an SOS signal after he replaced a broken resistor with a piece of pencil lead. In the end, this saved the explorers.

Resistors are important components in electronic devices and can be used as individual components or as parts of integrated circuits. Discrete resistors are classified according to their use, the type of current-voltage relationship, safety specifications, mounting method, the way their resistance changes, manufacturing specifications, and the amount of thermal emissions. They are marked in circuit diagrams as in the image below.

Resistors can be connected either in series or in parallel. When the connection is in series, the overall resistance of the circuit is the sum of resistances of each resistor:

R = R₁ + R₂ + … + R_n

When the connection is in parallel, then the total resistance of the circuit is:

R = R₁ × R₂ × … × R_n/(R₁ + R₂ + … + R_n)

Resistors are classified based on their use into:

• Resistors for general use;
• Specialized resistors.

As for the way their resistance changes, resistors are divided into:

• Fixed resistors;



PCB-mount trimmer potentiometer

• Trimmer pots or trimpots
• Slide pots or thumb pots (potentiometers).

Based on the mounting method, resistors are classified as:

• Those for printed circuitry;
• Those used in point-to-point construction;
• Resistors for microchips and microelectronic modular assembly.

Classification based on the type of current-voltage relationship is as follows:

• Linear fixed resistors: they are mostly general-purpose components used for voltage division, for limiting electric current, and for power dissipation;
• Varistors: their resistance depends on the external voltage and significantly drops when a certain threshold is reached; they are used to protect equipment from pulse surges and rapid changes in voltage;
• Thermistors: their resistance depends on temperature. There are thermistors with negative as well as with positive temperature resistance coefficient, known as negative temperature coefficient (NTC) thermistors and positive temperature coefficient thermistors (PTC) or posistors. They are used in fire safety, temperature control systems, and temperature control circuits. Historically they were used in RF and microwave power measurements. When we turn on an old television set that uses a cathode ray tube, we create a magnetic field with waning amplitudes, because the display has a degaussing coil, which is turned on through a posistor. Thanks to this, a remnant magnetic field does not distort the colors on the display.



0.5 W axial-lead resistors on tape

• Photoresistors: their resistance is influenced by the lighting conditions. They are used as photosensors in tracing and tracking devices as well as in consumer photoelectric relays, in security systems, and in systems that automatically open doors and turnstiles, for example in the subway.
• Magnetoresistors: their resistance depends on the intensity of the magnetic field and they are used to measure magnetic induction and power and employed as sensors in touch-free switches, linear motion sensors, Hall effect sensors, and remote potentiometers.

Color Coding of Resistors

Resistors are color-coded according to their size and use. Color coding can be done in conjunction with alpha-numeric coding, and resistors can be marked with different color stripes if they are meant as discrete components. A given symbol can mark decimal points. Ohms are marked as R and E, kiloohms — as K, and megohms — as M. For example, 3R3 means 3.3 Ω, 33E = 33 Ω, 4К7 = 4.7 kΩ, М56 = 560 kΩ, 1М0 = 1.0 MΩ.

Small resistors used as discrete components are marked with color stripes in accordance with established coding tables. We could find information on coding in books but it is much easier to find it online.

Surface-mount device (SMD) resistors are coded with three or four digits or three symbols. The codes can be determined by checking a table or looking up this information online.

Measuring Resistors

The most practical way of determining the specifications of a given resistor and checking if it is working correctly is to measure its resistance directly by using a multimeter. If you test resistors installed in a device, you must remember that you can only test resistors if your device is not powered. Note that the results of measurements of installed resisters will be incorrect.

References

This article was written by Sergey Akishkin

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Electrical Engineering

Electrical engineering is a field of engineering that deals with the study and application of electricity, electronics, and electromagnetism. It covers subtopics like power, electronics, control systems, signal processing and telecommunications.

Electrical Resistance Converter

The electrical resistance of a circuit component is the opposition to the passage of an electric current through that component.

The SI unit of electrical resistance is the ohm (Ω), while electrical conductance is measured in siemens (S). The ohm is defined as a resistance between two points of a conductor when a constant potential difference of 1 volt applied to these points produces a current of 1 ampere.

Using the Electrical Resistance Converter Converter

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