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Russian physicist

(1804-1865)1834 Lenz’s Law

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There is an induced current in a closed conducting loop if and only if the magnetic flux through the loop is changing. The direction of the induced current is such that the induced magnetic field always opposes the change in the flux.

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Lenz’s law obeys the law of conservation of energy and if the direction of the magnetic field that creates the current and the magnetic field of the current in a conductor are in same direction, then these two magnetic fields would add up and produce the current of twice the magnitude and this would in turn create more magnetic field, which will cause more current and this process continuing on and on leads to violation of the law of conservation of energy.

If you wrap your fingers around the coil in the direction of the current, your thumb points north.

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What DIRECTION OF CURRENT WHEN A MAGNET IS PUSHING TOWARDS A LOOP:

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2 Direction of induced current

In both cases, magnet moves against a force.Work is done during the motion & it is transferred as electrical energy.

Induced I always flows to oppose the movement which started it.

b Lenz's law

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Current induced along a coil

Indicate the direction of the induced I. Explain.

(i)

When magnet’s N-pole is moving into coil,induced I flows in such a direction as to produce a N-poleto oppose the approaching of magnet.

Lenz’s law

I

S N

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Current induced along a coil

Indicate the direction of the induced I. Explain.

(iii)

When magnet’s S-pole is leaving the coil,

induced I flows in such a direction as toproduce a N-pole to oppose the leaving of magnet.

I

N S

Alternating current through the coil

What happens to Iron core?

What will happen to the ring?

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The changing magnetic field in the coil due to the change in current induces a current in the metal ring. Lenz’s Law states that the magnetic field in the ring opposes the magnetic field of the coil and forces the ring to fly away.

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The copper tube "sees" a changing magnetic f ield from the fal l ing magnet. This changing magnetic f ield induces a current in the copper tube.

The induced current in the copper tube creates its own magnetic f ield that opposes the magnetic f ield that created it.

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