# what is the unit of resistance

The unit for measuring the resistance of direct current is the ohm (abbreviated as Ω), named after the German physicist and mathematician Georg Simon Ohm (1789-1854). According to ohm’s law, the resistance R is the ratio between the potential difference U across the conductor and the current I flowing through the conductor: Hence this value is as follows: 1 Ω = 1 V / A. This definition of ohm SI is really not feasible to do Read: what is the unit of resistance Due to the unusual reproducibility of Hall quantum resistors, perfect long-term stability and worldwide uniformity, ohm can be found to be some part of the von-Klitzing constant. Since 1990, on the basis of CIPM (Comité International des Poids et Mesures) recommendations, worldwide resistance comparisons and calibrations must be reduced to a fixed numerical value of the von-Klitzing constant. , RK-90 = 25812,807 Ω90 . Giving this conventional reference value for the von Klitzing constant has significant practical advantages in terms of maintenance and unit popularity of the ohm. At the same time, however, this also meant that the conventional unit Ω90 did not comply with the International System of Units (SI) in effect at that time. For example, SI recognition of the ohm is possible with Thompson-Lampard capacitors (capacitance can be calculated; due to the complexity of the respective measurement setup, achievable accuracy is low. more than reproducibility of quantum Hall resistors Read more: What is a “Dime” in the NBA On May 20, 2019, an SI revision came into effect according to which the SI value for the von constant Klitzing RK = h/e2 can be calculated using precisely defined values ​​for the fundamental charge e and the Planck constant h. This makes it possible to realize the ohm through the use of a Hall resistor. quantum in SI In PTB the unit of resistance is realized from the quantum resistor Hall a superconducting solenoid In order to ensure that the Hall resistance value is accurately quantified, several criteria are established. Acceptance must be met [Delahaye, Jeckelmann, Metrologia 40, 217-223 (2003)]. Firstly, longitudinal resistance should be zero because vanishing longitudinal resistance is a measure for complete quantification (otherwise correction must be applied). Furthermore, all the contact resistances of the quantum Hall device should be sufficiently small. Before each calibration, these criteria must be confirmed experimentally. Furthermore, resistance values ​​calibrated at the PTB and at other national metrology institutes must be compared over time, to ensure worldwide uniformity of the ohm unit of resistance. To popularize the device, it turns out that it is possible to calibrate a typical 100Ω resistor with known drift behavior about twice a year, using a cold current comparator. With this 100Ω working resistance, the calibration for PTB’s customers was carried out by Working Group 2.11. Only in the case of special calibrations that require a relative uncertainty of 10-9 (or less), the calibrated resistance is measured directly with the quantum Hall resistor (i.e. no intermediate step with a 100Ω resistor). One example is the precision measurement in graphene as part of a research project. Read more: What’s the difference between jokesSet of 1Ω resistors from “The Leeds & Northrup Co.” as previously used to preserve ohm.Back to Home AG 2.61 Read more: What does ace tattoo mean