Lenz's Law — Study Materials Flashcards

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Lenz's Law

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Lenz's law states that an induced current in a conductor due to a change in magnetic flux will flow in a direction that opposes the change producing it. It explains the direction of the induced current and ensures conservation of energy by opposing the motion that produces the flux change.

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Magnetic Flux

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Magnetic flux is the total number of magnetic field lines passing through a surface or conductor. A change in magnetic flux through a loop is what causes electromagnetic induction.

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Magnetic Induction

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Magnetic induction is the process where a changing magnetic environment around a conductor generates an emf or potential difference. When a magnet is moved relative to a conductor, an emf is induced that can produce current in the conductor.

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Induced EMF

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Induced emf is the electromotive force generated in a conductor when the magnetic flux through it changes. This induced emf drives the induced current according to the circuit's resistance and configuration.

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Induced Current

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Induced current is the electric current produced in a conductor due to an induced emf from changing magnetic flux. The direction of this current is determined by Lenz's law and changes with the motion of the magnet.

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Direction of Current

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The direction of the induced current is such that the magnetic field it creates opposes the change in the original magnetic flux. If the magnet approaches the coil the current will flow one way; if it moves away the current reverses.

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Induced Magnetic Field

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The induced magnetic field is the field produced by the induced current in the conductor or coil. Its polarity is arranged to oppose the change in the external magnetic flux according to Lenz's law.

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Polarity Change

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The polarity of the induced magnetic field changes with the direction of the induced current. When the magnet's motion reverses, the polarity of the induced field also reverses to continue opposing the flux change.

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Magnet Approaching

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When a magnet moves toward a coil the induced current flows in a direction (clockwise in the given example) that produces a magnetic pole opposing the approaching magnet. The induced pole is the same polarity as the approaching pole, causing repulsion.

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Magnet Receding

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When a magnet is moved away from a coil the induced current flows in the opposite direction (anti-clockwise in the example) and produces a magnetic pole that attracts the receding magnet. The induced pole is opposite in polarity to the magnet's near face.

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Clockwise Current

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In the slide example, clockwise induced current corresponds to the induced magnetic field having a south polarity facing the approaching magnet. This south-facing induced pole repels the south pole of the approaching magnet.

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Anticlockwise Current

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In the slide example, anticlockwise induced current corresponds to the induced magnetic field having a north polarity facing the receding magnet. This north-facing induced pole attracts the receding magnet's south pole.

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Repulsion

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Repulsion occurs when like magnetic poles (e.g., south facing south) are brought near each other. Lenz's law predicts induced currents that create such repelling poles when necessary to oppose an increase in flux.

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Attraction

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Attraction occurs when unlike magnetic poles (north and south) are brought near each other. Induced currents can produce poles that attract a receding magnet, opposing the decrease in magnetic flux.

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Electromagnet

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An electromagnet is a magnet created by running current through a coil of wire, producing a magnetic field. Moving an electromagnet relative to a conductor induces emf and current in the conductor just as a permanent magnet would.

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Conductor

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A conductor is a material that allows electric charges to flow when an emf is applied or induced. In induction experiments, coils of conducting wire are commonly used to observe induced currents.

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Coil

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A coil is a looped conductor that enhances the effect of changing magnetic flux by providing multiple turns for flux to pass through. More turns increase the induced emf for the same change in flux.

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Change in Flux

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Change in flux refers to any variation in the magnetic flux through a surface over time, caused by motion, field strength changes, or orientation changes. It is the essential cause of electromagnetic induction and induced emf.

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Opposing Motion

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Opposing motion describes how the induced magnetic field produces forces that resist the relative motion causing the flux change. This opposition is the mechanism by which energy is conserved in induction processes.

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AC Current in Induction

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Induced current can be alternating if the magnetic flux through the conductor changes direction or oscillates. The direction of induced current follows the motion of the magnet and reverses when the motion or flux change reverses.