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Lenz’s law states that the current induced in a circuit due to a change in a magnetic field is directed to oppose the change in flux and to exert a mechanical force which opposes the motion.
What this means is that the polarity of an induced emf opposes the change in magnetic flux that produced it. When a magnetic field induces a current in a coil, the induced current generates its magnetic field, opposite to the inducing magnetic field. An induced current always opposes the motion that started it. Lenz’s law is useful when needing to determine the direction of an induced current and the magnetic field induced by the current.
The law is named after the German physicist Emil Lenz, who developed it in 1834.
The law is known as a qualitative law. This means that it specifies the direction of the current that is induced but makes no account for the magnitude.
The law can be used to predict the direction of a voltage or the drag force of eddy currents exerted on moving objects in a magnetic field.
conservation of energy
If the current did not oppose the magnet’s magnetic field, the induced magnetic field would be in the same direction as the inducing magnetic field. This would be problematic as the two magnetic fields would up, creating a larger magnetic field. This magnetic field would then induce another recurrent in the coil, twice the magnitude of the original current. There would be an endless loop of induced currents and magnetic fields, violating the conservation of energy law.
When a circuit contains an inductive component, such as a motor, when the power is removed, a back emf is created. This can cause damage to components. One way of stopping any damage is by placing a diode across the motor. This gives the current somewhere to go.