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dopo passare al TUTORIAL

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What happens when you put an electrical current in a magnetic field? Although it looks like magic, it's really the Lorentz force.

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Learn the Lorentz force with the help of this tutorial, in which a wire fashioned into a pendulum moves inside a magnetic field.

A charged particle moving through a magnetic field experiences a force that is at right angles to both the direction in which the particle is moving and the direction of the applied field. This force, known as the Lorentz force, develops due to the interaction of the applied magnetic field and the magnetic field generated by the particle in motion. The phenomenon is named for Dutch physicist Hendrik Lorentz, who developed an equation that mathematically relates the force to the velocity and charge of the particle and the strength of the applied magnetic field.

The Lorentz force is experienced by an electric current, which is composed of moving charged particles. The individual magnetic fields of these particles combine to generate a magnetic field around the wire through which the current travels, which may repel or attract an external magnetic field. This tutorial demonstrates the Lorentz force exerted on a wire that carries current through the field of a permanent horseshoe Magnet (field lines always move from a magnet's north pole to its south). The wire is arranged in a kind of pendulum so that it can move back and forth. Click on the Knife Switch to start the flow of current. The wire will swing in a direction perpendicular both to the magnet's field and to the movement of the charged particles. Changing the direction of current flow by clicking the Flip Battery button, or the direction of the magnetic field by clicking the Flip Magnet button, will reverse the direction of the Lorentz force. Using the Show Wire Field Lines and Show Magnet Field Lines radio buttons will reveal the interplay of these invisible forces. The Reset button can be used to return the magnet and battery to their original positions.

You can predict which way the wire will move by using the left-hand rule. You need to contort your hand in a bit of an unnatural position for this rule: If your index finger points in the direction of a magnetic field, and your middle finger, at a 90 degree angle to your index, points in the direction of electrical current, then your extended thumb (forming an L with your index) points in the direction of the Lorentz force exerted upon that particle, and the direction in which the wire shifts in the tutorial.

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Learn the Lorentz force with the help of this tutorial, in which a wire fashioned into a pendulum moves inside a magnetic field. A charged particle moving through a magnetic field experiences a force that is at right angles to both the direction in which the particle is moving and the direction of the applied field.

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Electric motors turn electricity into motion by exploiting electromagnetic induction.

A simple direct current (DC) motor is illustrated below.

The motor features a permanent horseshoe magnet (called the stator because it's fixed in place) and an turning coil of wire called an armature (or rotor, because it rotates). The armature, carrying current provided by the battery, is an electromagnet, because a current-carrying wire generates a magnetic field; invisible magnetic field lines are circulating all around the wire of the armature.

The key to producing motion is positioning the electromagnet within the magnetic field of the permanent magnet (its field runs from its north to south poles). The armature experiences a force described by the left hand rule. This interplay of magnetic fields and moving charged particles (the electrons in the current) results in the torque (depicted by the green arrows) that makes the armature spin. Use the Flip Battery button to see what happens when the flow of current is reversed. Take advantage of the Applet Speed slider and Pause button to visualize these forces better.

A single, 180-degree turn is all you would get out of this motor if it weren't for the split-ring commutator - the circular metal device split into halves (shown here in red and blue) that connects the armature to the circuit. Electricity flows from the positive terminal of the battery through the circuit, passes through a copper brush to the commutator, then to the armature. But this flow is reversed midway through every full rotation, thanks to the two gaps in the commutator. This is a clever trick: For the first half of every rotation, current flows into the armature via the blue portion of the commutator, causing current to flow in a specific direction (indicated by the black arrows). For the second half of the rotation, though, electricity enters through the red half of the commutator, causing current to flow into and through the armature in the opposite direction. This constant reversal essentially turns the battery's DC power supply into alternating current, allowing the armature to experience torque in the right direction at the right time to keep it spinning.

View an animated video about DC motors.

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Electric motors turn electricity into motion by exploiting electromagnetic induction. A simple direct current (DC) motor is illustrated below. The motor features a permanent horseshoe magnet (called the stator because it's fixed in place) and an turning coil of wire called an armature (or rotor, because it rotates).

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Questions  20.6 to 20.8
WORKBOOK ex 1(Using electromagnetism)

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LAB L. Montaigne

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Manip Lycée Montaigne de Bordeaux: rail de Laplace; fil de Laplace

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Activity 20.1
Worksheet 20.1

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elettromagnete

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Working Principle of DC Motor (animation of elementary model)

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magnetic field lines

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PH EM MF DEMO 70001A V1025 2D Magnetic Field Demonstrations Simple Wire Coils

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2- magnetic field around a straight wire

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2- magnetic field around a straight wire

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min 2.40

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neodimio