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In figure (a), the magnet is moving into the coil. Therefore the current in the coil move in such a way to OPPOSE (negative sign) the magnet's flux. The image shows the current (I) moving upwards on the portion of the coil that is extending from the page. The current is moving into the page at the top of the coil.
Lenz's Law - The Negative Sign
The induced current will be in such a direction to oppose the change in magnetic flux that created the current.
(a) Due to Faraday's Law, a moving magnetic field will induce a current into a wire. The current (I) within the coil will be determined by the
(b) According to the right hand rule (RHR), the magnetic field in (b) as shown, with the north pole facing to the left.
LENZ's LAW Problem Solving Strategy:
LENZ's LAW Problem Solving Strategy:
To use Lenz’s law to determine the directions of the induced magnetic fields, currents, and emfs:
Make a sketch of the situation for use in visualizing and recording directions.
Determine the direction of the magnetic field B.
Determine whether the flux is increasing or decreasing.
Now determine the direction of the induced magnetic field B. It opposes the change in flux by adding or subtracting from the original field.
Use RHR-2 to determine the direction of the induced current I that is responsible for the induced magnetic field B.
The direction (or polarity) of the induced emf will now drive a current in this direction and can be represented as current emerging from the positive terminal of the emf and returning to its negative terminal.
The rows of rare earth magnets (protruding horizontally) are used for magnetic braking in roller coasters. (credit: Stefan Scheer, Wikimedia Commons)
Electromagnetic Braking
Electromagnetic Braking
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