Beatrice Lang
The ohm, or Ω, is the standard unit of electrical resistance in the International System of Units (SI). It is named after German physicist Georg Ohm, who, in 1827, published a formula that stated that the amount of electric current flowing through a conductor is directly proportional to the voltage imposed on it. This became known as Ohm's Law, which is used to calculate the relationship between voltage, current, and resistance in an electrical circuit.
| Characteristics | Values |
|---|---|
| What is an ohm? | A measurement of resistance and the standard unit of electrical resistance in the International System of Units (SI) |
| Symbol | Ω, the uppercase Greek letter omega |
| Named after | German physicist Georg Ohm (1789-1854) |
| Formula | V = IR or V = I x R, where V is voltage, I is current, and R is resistance |
| Application | Used to calculate the relationship between voltage, current, and resistance in an electrical circuit |
| Impedance | In alternating current circuits, electrical impedance is also measured in ohms |
| Conductance and Admittance | Siemens (S) is the SI unit of electric conductance and admittance, with 1 Siemens = 1 Ω^-1 |
| Power Calculation | The power dissipated by a resistor can be calculated using a combination of Ohm's Law and Joule's Law: P = VI, where P is power, V is voltage, and I is current |
| Linear vs. Non-linear Resistors | Linear resistors have a constant resistance value over all applied voltages or currents; non-linear resistors have a value that may vary depending on the applied voltage or current |
| Limitations | Ohm's Law is not applicable to unilateral electrical elements like diodes and transistors, as well as non-ohmic conductors such as semiconductors |
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Ohm's Law
It is important to note that Ohm's Law does not apply to all materials. Some materials are called non-ohmic, meaning they do not obey Ohm's Law. Additionally, when working with alternating current (AC) circuits, impedance, inductance, and capacitance come into play and must be considered in the calculations.
Overall, Ohm's Law is a fundamental concept in the study of electricity and electronics, providing a simple and useful tool for analyzing electrical circuits and troubleshooting potential issues.
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Electrical resistance
The SI unit of electrical resistance is the ohm (Ω), named after German physicist Georg Ohm (1789-1854). The ohm is defined as the electrical resistance between two points of a conductor when a constant potential difference of one volt (V) is applied, and a current of one ampere (A) is produced, provided that there is no electromotive force in the conductor. The ohm is part of a coherent system of units, along with the watt, volt, and ampere, which are used in Ohm's Law.
Ohm's Law is a formula that describes the relationship between voltage, current, and resistance in a circuit. It states that voltage equals the current multiplied by the resistance, or E = IR, where E is voltage, I is current, and R is resistance. This law is incredibly useful as it allows technicians to calculate any one of the three values if they know the other two. For example, if a circuit has a 9V battery and produces a 0.5A current, the resistance can be calculated as 18 ohms.
Resistance is influenced by several factors, including the material, size, and shape of the object, as well as temperature. For instance, a wire's resistance is higher if it is long and thin, and lower if it is short and thick. Materials like rubber, which are insulators, tend to have very high resistance, while conductors like metals have low resistance. Resistors are components that are specifically designed to resist the flow of electricity in a circuit, and they are used to adjust current and voltage.
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Voltage, current and resistance
Voltage, current, and resistance are three fundamental concepts in electricity. Voltage, current, and resistance are related to one another, as described by Ohm's Law. This law was discovered by German physicist Georg Simon Ohm and published in his 1827 paper, "The Galvanic Circuit Investigated Mathematically".
An electric circuit is formed when a conductive path is created to allow electric charge to continuously move. This continuous movement of electric charge through the conductors of a circuit is called a current, often referred to in terms of "flow," similar to the flow of a liquid through a pipe. The force that motivates charge carriers to "flow" in a circuit is called voltage. Voltage is a measure of the potential difference between two points in a circuit and is applied across a wire or an electric component. It is a specific measure of potential energy that is always relative between two points. The "pressure" pushing the electrons along is called voltage, and it is measured in volts.
The number of electrons in motion in a circuit is called the current, and it is measured in amps. Current refers to the amount of charge that flows in any part of the conductor per time interval. Current tends to move through the conductors with some degree of friction or opposition to motion, which is called resistance. Resistance is the measure of opposition to the current in a circuit. It is the standard unit of electrical resistance in the International System of Units (SI) and is measured in ohms.
The relationship between voltage, current, and resistance is given by Ohm's Law, which states that the current in a wire is proportional to the voltage across it but inversely proportional to resistance. Ohm's Law can be expressed as I = V/R, where I is the current in amperes, V is the voltage in volts, and R is the resistance in ohms. This formula can be rearranged to find any one of the three quantities if the other two are known.
A water hose analogy can help illustrate the relationship between voltage, current, and resistance. In this analogy, the voltage is equivalent to the water pressure, the current is equivalent to the flow rate, and the resistance is like the pipe size. If you increase the pressure in a tank, more water will flow out of the hose, similar to how increasing the voltage in an electrical system results in a greater current flow. On the other hand, if there are more constrictions in the hose, the amount of water flowing decreases, just as an increase in resistance leads to a decrease in current.
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Impedance
Ohm's Law, introduced by German mathematician and physicist Georg Simon Ohm, states that there is a proportional relationship between voltage, current, and resistance in an electrical circuit. This law is used to calculate a circuit's electrical quantities. The unit of electrical resistance in the International System of Units (SI) is the ohm, represented by the uppercase Greek letter omega (Ω).
The symbol for impedance is 'Z', and its unit is the same as that of resistance, the ohm (Ω). Impedance is usually represented as a complex number, with the real part representing resistance (R) and the imaginary part representing reactance (X). The magnitude of impedance can be calculated using the Pythagorean theorem.
The impedance of a device can be calculated by complex division of the voltage and current. It can also be defined as the ratio of the phasor voltage across the element to the phasor current through the element. Measurements of impedance are typically carried out at one frequency, but the variation of device impedance over a range of frequencies may also be of interest. The measurement of impedance requires the determination of the magnitude of voltage and current, as well as the phase difference between them.
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Georg Ohm
Georg Simon Ohm, born on March 16, 1789, in Erlangen, Bavaria (now part of Germany), was a German physicist and mathematician. He is well-known for formulating Ohm's Law, which describes the mathematical relationship between electrical current, resistance, and voltage.
Ohm came from a humble background and faced financial struggles throughout his life. He was the son of a locksmith and received his early education from his father, who had a vast knowledge of various subjects despite lacking formal schooling. Ohm later attended the University of Erlangen, where he excelled in advanced mathematics. However, he did not apply himself fully to his studies, which led to his father sending him to Switzerland at the age of 17.
In Switzerland, Ohm began his career as a mathematics teacher at a school in Gottstadt bei Nidau in 1806. He left this position in 1809 to become a private tutor in Neuchâtel while continuing his private studies in mathematics. The following year, he returned to the University of Erlangen, where he obtained his doctorate in 1811. After graduating, Ohm joined the faculty as a lecturer in mathematics, but he soon left due to unsatisfactory pay.
Ohm then took up various teaching positions, including at a school in Bamberg and the Jesuit Gymnasium of Cologne, where he also taught physics. It was during his time in Cologne that Ohm began his experimental work on electricity and published his findings in 1827. His work, "Die galvanische Kette, mathematisch bearbeitet" ("The Galvanic Circuit Investigated Mathematically"), introduced Ohm's Law and had a significant impact on the theory and applications of current electricity.
Despite the importance of his work, Ohm's Law was initially poorly received, leading him to resign from his post in Cologne. He later joined the Polytechnic School of Nürnberg in 1833, and his contributions finally gained recognition. In 1841, he received the prestigious Copley Medal from the Royal Society in England and was honoured with foreign membership the following year. Ohm's standing among fellow scientists continued to improve, and he was appointed as a professor at the University of Munich in 1849, ending his long search for a suitable teaching position. He was also awarded the physics chair at the university shortly before his death on July 6, 1854.
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Frequently asked questions
An ohm is the unit of electrical resistance in the International System of Units (SI). It is named after German physicist Georg Ohm.
Ohm's Law states that the voltage across a conductor is directly proportional to the current flowing through it, provided all physical conditions and temperatures remain constant. This relationship can be written mathematically as V = IR, where V is voltage, I is current, and R is resistance.
Ohm's Law is one of the most basic and important laws of electric circuits. It can be used to calculate a circuit's electrical quantities, such as current levels, voltage supplies, and voltage drops.
