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Related Concept Videos

Torque On A Current Loop In A Magnetic Field01:13

Torque On A Current Loop In A Magnetic Field

The most common application of magnetic force on current-carrying wires is in electric motors. These consist of loops of wire, which are placed between the magnets with a magnetic field. When current flows through the loops, the magnetic field applies torque, which causes the shaft to rotate, thus converting electrical energy to mechanical energy.
Consider a rectangular current-carrying loop containing N turns of wire, placed in a uniform magnetic field. The net force on a current-carrying loop...
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Magnetic forces on wires carrying current are most frequently applied in motors. A DC motor is a device that converts electrical energy into mechanical work. In motors, wire loops are enclosed in a magnetic field. When current flows through the loops, the magnetic field applies torque, which causes the shaft to rotate. The direction of the current is reversed once the loop's surface area is lined up with the magnetic field, causing a constant torque on the loop. During the process, commutators...
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Consider a circular loop with a radius a, that carries a current I. The magnetic field due to the current at an arbitrary point P along the axis of the loop can be calculated using the Biot-Savart law.
Magnetic Force On Current-Carrying Wires: Example01:22

Magnetic Force On Current-Carrying Wires: Example

In a magnetic field, moving charges encounter a force. If a wire contains these moving charges, i.e., if the wire is carrying a current, then a force acts on the wire as well. Consider a pair of flexible leads holding a wire that is 40 cm long and 10 g in weight in a horizontal position. The wire is placed in a constant magnetic field of 0.40 T, as shown in Figure 1(a). Determine the magnitude and direction of the current flowing in the wire needed to remove the tension in the supporting leads.
Types Of Superconductors01:28

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A superconductor is a substance that offers zero resistance to the electric current when it drops below a critical temperature. Zero resistance is not the only interesting phenomenon as materials reach their transition temperatures. A second effect is the exclusion of magnetic fields. This is known as the Meissner effect. A light, permanent magnet placed over a superconducting sample will levitate in a stable position above the superconductor. High-speed trains that levitate on strong...
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Scalable Quantum Integrated Circuits on Superconducting Two-Dimensional Electron Gas Platform
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Published on: August 2, 2019

Persistent current in small superconducting rings.

Georg Schwiete1, Yuval Oreg

  • 1Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot, 76100, Israel.

Physical Review Letters
|August 8, 2009
PubMed
Summary
This summary is machine-generated.

Persistent currents persist in small superconducting rings despite theoretical predictions of zero transition temperature. Cooper pair fluctuations, not mean-field condensation, drive this significant persistent current.

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Area of Science:

  • Condensed matter physics
  • Quantum mechanics

Background:

  • Superconducting rings exhibit persistent currents influenced by magnetic flux.
  • Mean field theory predicts zero transition temperature for small rings near half-integer flux.

Purpose of the Study:

  • Investigate the role of fluctuating Cooper pairs in persistent currents.
  • Analyze persistent currents in superconducting rings of varying sizes relative to coherence length.
  • Examine the impact of magnetic flux on Cooper pair fluctuations.

Main Methods:

  • Theoretical analysis of Cooper pair fluctuations.
  • Mean field theory application for small rings (coherence length xi > radius R).
  • Analytical calculation of susceptibility in the critical region for larger rings (R >> xi).

Main Results:

  • A large persistent current is predicted to persist even when mean field theory suggests zero transition temperature.
  • Cooper pair fluctuations, which do not condense, are responsible for the persistent current in small rings.
  • For larger rings, susceptibility calculations reveal competition between two interacting complex order parameters in the critical region.

Conclusions:

  • Cooper pair fluctuations play a crucial role in maintaining persistent currents in superconducting rings, particularly in small systems.
  • The behavior of persistent currents is size-dependent, with fluctuations dominating in small rings and complex order parameter interactions in larger ones.
  • Theoretical predictions need to account for fluctuation effects beyond mean field theory to fully understand superconductivity in finite systems.