Beatrice Lang
Electrical resistance is the property of an object or substance to resist or oppose the flow of an electric current. The SI unit of electrical resistance is the ohm, represented by the uppercase Greek letter omega (Ω). The ohm is defined as the electrical resistance between two points of a conductor when a constant potential difference of one volt (V), applied to these points, produces in the conductor a current of one ampere (A). The ohm is named after German physicist Georg Ohm, who studied the relationship between voltage, current, and resistance.
| Characteristics | Values |
|---|---|
| Unit of electrical resistance | Ohm (Ω) |
| Symbol | Ω (uppercase Greek letter omega) |
| Named after | German physicist Georg Ohm (1789–1854) or Georg Simon Ohm (1784-1854) |
| Definition | Electrical resistance between two points of a conductor when a constant potential difference of one volt (V), applied to these points, produces in the conductor a current of one ampere (A) |
| Reciprocal quantity | Electrical conductance measured in Siemens (S) |
| Non-linear resistors | Value may vary depending on the applied voltage (or current) |
| Linear resistors | Resistance is approximately constant within a certain range of voltages, temperatures, and other parameters |
| Examples of linear resistors | Wire, resistor, or other elements |
| Formula | R = E/I (ohms = volts / amps) |
| Specific resistance or resistivity | Measured by the unit ohm-metre or ohm-m |
| Other units of resistance | Abohm, megohm, statohm, preece, and planck-impedance |
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What You'll Learn
- The ohm is the SI unit for electrical resistance
- Resistance is the measure of opposition to the flow of electric current
- Resistance is dependent on the material and shape of an object
- The ohm is defined as the electrical resistance between two points of a conductor
- The ohm is named after German physicist Georg Ohm
The ohm is the SI unit for electrical resistance
The ohm (Ω) is the SI unit for electrical resistance. It is named after German physicist Georg Ohm (1784/1789–1854), who studied the relationship between voltage, current, and resistance. Ohms are used to measure how much an object or substance resists or opposes the flow of an electric current.
The ohm is defined as the electrical resistance between two points of a conductor when a constant potential difference of one volt (V), applied to these points, produces in the conductor a current of one ampere (A), provided that the conductor is not the seat of any electromotive force. This relationship is known as Ohm's Law.
Ohm's Law states that the voltage (V) across a circuit is equal to the current (I) flowing through it multiplied by the resistance (R). In other words, resistance is the ratio of voltage to current. For example, if the voltage across a circuit is 240 volts and the current is 4 amps, the resistance is 60 ohms (240 ÷ 4 = 60 Ω).
The ohm belongs to a coherent system of units, where each quantity has its corresponding SI unit: watt for power (P), ohm for resistance (R), volt for voltage (V), and ampere for current (I). This formula remains valid when these units are used and thought of as being cancelled or omitted.
The ohm is also used in alternating current circuits to measure electrical impedance. Additionally, there are specific resistance units derived from the ohm, such as the ohm-metre or ohm-m, and other popular units of resistance like Abohm, megohm, statohm, preece, and planck-impedance.
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Resistance is the measure of opposition to the flow of electric current
Ohm's Law states that the voltage (V) across a circuit is equal to the current (I) flowing through it multiplied by the resistance (R). Mathematically, this relationship can be expressed as V = IR. This law holds true for a wide range of materials and conditions, where the voltage and current are directly proportional to each other. However, there are also cases where the current is not proportional to the voltage, and the resistance varies with these factors. Such materials are called nonlinear or non-ohmic, and examples include diodes and fluorescent lamps.
The resistance of an object depends on two primary factors: the material it is made of and its shape. For instance, a thick copper wire has lower resistance than a thin copper wire of the same length. Additionally, the length of the object also plays a role, with longer objects generally exhibiting higher resistance. The nature of a material is crucial, as substances with high conductivity, such as metals, tend to have lower resistance, while insulators like rubber have higher resistance.
Resistance is an inherent property of all materials, and it influences the flow of electric current. It can be used beneficially in electrical systems, such as in toasters, where high resistance generates heat to toast bread. The concept of resistance has led to the development of resistors, which are specifically designed to introduce a known amount of resistance into a circuit. Resistors are made from a variety of materials, depending on factors such as the desired resistance value and cost.
In conclusion, resistance is a critical concept in electrical systems, representing the opposition to the flow of electric current. Its measurement in ohms provides valuable insights into the behaviour of circuits and materials. By understanding resistance and its relationship with voltage and current through Ohm's Law, engineers and technicians can design and troubleshoot circuits effectively, ensuring optimal performance and functionality.
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Resistance is dependent on the material and shape of an object
The ohm (Ω), named after German physicist Georg Ohm, is the SI unit of electrical resistance. It is defined as the electrical resistance between two points of a conductor when a constant potential difference of one volt (V), applied to these points, produces a current of one ampere (A) in the conductor.
The resistance of an object depends on the material it is made of and its shape. Objects made of electrical insulators like rubber tend to have very high resistance and low conductance, while objects made of electrical conductors like metals tend to have very low resistance and high conductance. This relationship is quantified by resistivity or conductivity. Resistivity is an intrinsic property of a material, independent of its shape or size, and it measures how strongly a material resists electric current. A low resistivity indicates a material that readily allows electric current.
The nature of a material is not the only factor in resistance and conductance; the size and shape of an object also play a role. For a given material, the resistance is inversely proportional to the cross-sectional area and proportional to the length. For example, a thick copper wire has lower resistance than a thin copper wire of the same length, and a long copper wire has higher resistance than a short copper wire of the same thickness. This is because the resistance of a uniform cylinder of length L, cross-sectional area A, and made of a material with resistivity ρ, is directly proportional to L and inversely proportional to A.
Other factors that can influence resistance include temperature and voltage. For example, the resistivity of metals typically increases as temperature increases, while the resistivity of semiconductors typically decreases. In some cases, materials can become superconductors with zero resistivity at very low temperatures. Additionally, in non-linear resistors, the resistance may vary depending on the applied voltage or current.
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The ohm is defined as the electrical resistance between two points of a conductor
The ohm, represented by the uppercase Greek letter omega (Ω), is the standard unit of electrical resistance in the International System of Units (SI). It is one of the derived units defined in the SI standard, meaning it is based directly or indirectly on the standard's fixed constants. The ohm is named after German physicist Georg Ohm (1789-1854), who discovered the relationship between voltage, current, and resistance in an electrical circuit, now known as Ohm's Law.
Ohm's Law states that there is a proportional relationship between voltage, current, and resistance in an electrical circuit. In other words, the amount of electric current through a metal conductor in a circuit is directly proportional to the voltage impressed across it, for any given temperature. This relationship can be expressed algebraically as voltage (E) being equal to current (I) multiplied by resistance (R).
The ohm is used to measure resistance in both direct current (DC) and alternating current (AC). In a DC circuit, the electric charge flows in only one direction, while in an AC circuit, the electric charge oscillates back and forth. In both types of circuits, voltage, current, and resistance are important quantities. Voltage is the difference in charge between two points, caused by the pressure that forces the current to flow and is measured in volts. Current is the rate at which the current flows and is measured in amperes or amps. Resistance is the rate at which a material resists the current's flow and is measured in ohms.
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The ohm is named after German physicist Georg Ohm
The ohm is the unit of electrical resistance in the International System of Units (SI). It is represented by the uppercase Greek letter omega (Ω). The ohm is named after German physicist Georg Simon Ohm, who lived from 1789 to 1854.
Georg Ohm was born in Erlangen, Bavaria (now part of Germany) and was the son of a locksmith. He received a diverse education from his father in subjects such as mathematics, physics, chemistry, and philosophy. However, his father was concerned about his son's dedication to studies and sent him to the University of Erlangen in 1805. Unfortunately, Ohm did not fare well there and dropped out after three semesters, relocating to Switzerland, where he became a mathematics teacher.
Ohm eventually returned to the University of Erlangen in 1809 and received his doctorate in 1811. He joined the faculty as a lecturer in mathematics but left due to dissatisfaction with his salary. Ohm then took up various teaching positions, including at a school in Cologne, where he had access to a physics laboratory. This allowed him to begin experimenting with electricity and magnetism, which were subjects of heavy investigation at the time.
Ohm's work culminated in the publication of "Die galvanische Kette, mathematisch bearbeitet" ("The Galvanic Circuit Investigated Mathematically") in 1827. This treatise included his electromagnetic theories and the components of what became known as Ohm's law. Ohm's law describes the mathematical relationship between electrical current, resistance, and voltage. It states that the current (I) flowing through a material with a given resistance is directly proportional to the applied voltage (V) and inversely proportional to the resistance (R).
Ohm's work greatly influenced the theory and applications of current electricity, and he was eventually recognized for his contributions. In 1841, he received the prestigious Copley Medal from the Royal Society in England, and he was appointed as a professor at the University of Munich in 1849, finally securing a stable and satisfactory position.
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Frequently asked questions
The unit for electric resistance is the ohm, symbolized by the Greek letter omega (Ω).
The formula for calculating resistance is R = V/I (ohms = volts / amps).
The SI unit of electrical resistance is the ohm (Ω).
