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Force On A Current Loop In A Magnetic Field01:17

Force On A Current Loop In A Magnetic Field

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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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Torque On A Current Loop In A Magnetic Field01:13

Torque On A Current Loop In A Magnetic Field

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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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Biot-Savart Law01:19

Biot-Savart Law

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The Biot-Savart law gives the magnitude and direction of the magnetic field produced by a current. This empirical law was named in honor of two scientists, Jean-Baptiste Biot and Félix Savart, who investigated the interaction between a straight, current-carrying wire and a permanent magnet.
A current-carrying wire creates a magnetic field in its vicinity. Consider an infinitesimal current element dl in a wire. The direction of vector dl is along the direction of the current. The total...
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Current Growth And Decay In RL Circuits01:30

Current Growth And Decay In RL Circuits

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The current growth and decay in RL circuits can be understood by considering a series RL circuit consisting of a resistor, an inductor, a constant source of emf, and two switches. When the first switch is closed, the circuit is equivalent to a single-loop circuit consisting of a resistor and an inductor connected to a source of emf. In this case, the source of emf produces a current in the circuit. If there were no self-inductance in the circuit, the current would rise immediately to a steady...
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Ampere's Law01:18

Ampere's Law

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A fundamental property of a static magnetic field is that it is not conservative, unlike an electrostatic field. Instead, there is a relationship between the magnetic field and its source, electric current. Mathematically, this is expressed in terms of the line integral of the magnetic field, which is also known as Ampère’s law. It is valid only if the currents are steady and no magnetic materials or time-varying electric fields are present.
Ampère's law states that for any...
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Electro-mechanical Systems01:19

Electro-mechanical Systems

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Electromechanical systems are intricate configurations that effectively combine electrical and mechanical elements to achieve a desired outcome. Central to many of these systems is the DC motor, a device that converts electrical energy into mechanical motion, enabling various applications ranging from simple fans to complex robotic mechanisms.
A key component of the DC motor is the armature, a rotating circuit positioned within a magnetic field. As an electric current passes through the...
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Related Experiment Video

Updated: Apr 18, 2026

The Modular Design and Production of an Intelligent Robot Based on a Closed-Loop Control Strategy
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The Modular Design and Production of an Intelligent Robot Based on a Closed-Loop Control Strategy

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Second laws for an information driven current through a spin valve.

Philipp Strasberg1, Gernot Schaller1, Tobias Brandes1

  • 1Institut für Theoretische Physik, Technische Universität Berlin, Hardenbergstrasse 36, D-10623 Berlin, Germany.

Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics
|January 24, 2015
PubMed
Summary
This summary is machine-generated.

We introduce a physical Maxwell's demon using quantum dots and spin valves. This model, equivalent to a Brownian ratchet, explores feedback control and its impact on extractable work and entropy production.

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Area of Science:

  • Quantum Thermodynamics
  • Statistical Mechanics
  • Mesoscopic Physics

Background:

  • Maxwell's demon is a thought experiment exploring the limits of the second law of thermodynamics.
  • Previous models often rely on abstract information processing or non-physical components.
  • Understanding the thermodynamic cost of information is crucial for developing new technologies.

Purpose of the Study:

  • To propose a physically realizable Maxwell's demon device.
  • To investigate the thermodynamic implications of discrete feedback control.
  • To analyze the relationship between entropy production and extractable work.

Main Methods:

  • Utilizing a spin valve interacting with electrons on a quantum dot tape.
  • Employing an exactly solvable model for system dynamics.
  • Analyzing a measurement-based discrete feedback scheme.

Main Results:

  • The proposed device is thermodynamically equivalent to existing models and can be interpreted as a Brownian ratchet demon.
  • Discrete feedback control leads to a different second law inequality, affecting bounds on extractable work.
  • An effective master equation reveals that entropy production rates are consistent with the second law for tape-based systems.

Conclusions:

  • A physically realizable Maxwell's demon based on quantum dots and spin valves is demonstrated.
  • Discrete feedback control offers new perspectives on the second law of thermodynamics and work extraction.
  • The study provides a unified framework for understanding entropy production in feedback-controlled systems.