Class 12 Physics Electromagnetic Induction Lenzs law

Lenz’s law

  • According to Lenz’s law:-The polarity of the induced emf is such that it tends to produce induced current in such a direction that it opposes the change in magnetic flux that produced it.
  • The (-) ive sign in given equatione= (-) (dΦ/dt)tells about the direction.
  • According to Faraday’s law whenever there is change in the magnetic flux, emf is induced, as aresult there will be induced current.
  • According to Lenz’s law the direction of the induced current will be such that it opposes the change in the magnetic flux.

For example:-

  • Consider a circuit where the magnetic flux is increasing, as a result flux will change and which induces the emf in the circuit, and as a result current will be induced in the circuit.
  • The direction of the induced current will be such that it will oppose the cause which induced it.
  • The induced current will be in such a direction that it decreases the magnetic flux.
  • Note: - The induced current will try to oppose the change which is producing it.

For example:-

  • Consider a setup which has a coil, a magnet and a galvanometer.
  • If the north pole of the magnet is brought near the coil, there will be a deflection in the galvanometer because of induced current.
  • The direction of the induced current will be such that it opposes the motion of the magnet towards coil.
  • Induced current will move the magnet away from the coil.
  • As the north polarity of the magnet is brought near the coil as a result the induced current will be in such a direction that the face of the coil will have north polarity.
  • The current will flow in the anti-clockwise direction.
  • If the South Pole of the magnet was nearer to the coil then the current will flow in clockwise direction.

Lenz’s law: supports Conservation of energy

  • Lenz’s law obeys conservation of energy.
  • Magnet is moving as a result current is getting induced and when the magnet is not moving there is no induced current in the coil.
  • There is a mechanical energy involved with the movement of the as magnet as a result mechanical energy is converted into electrical energy which is produced by the induced current.
  • Magnetic energy used in moving magnet is getting transformed into electrical energy which is produced by the induced current.
  • This shows that Lenz’s law supports conservation of energy where one form of energy is getting transformed into another form.
  • Work done in moving the magnet is dissipated by Joule heating produced by the induced current.

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