PHY 5.2 S2

• If electric currents produce a magnetic field, is it possible that a magnetic field can produce an electric current ?

  Possible
• • In this experiment, Faraday hoped by using a strong enough battery, a steady current in X would produce a current in a second coil Y but failed. • Faraday saw the galvanometer in circuit Y deflect strongly at the moment he closed the switch in circuit X. • And the galvanometer deflected strongly in the opposite direction when he opened the switch. • A steady current in X had produced no current in Y. • Only when the current in X was starting or stopping was a current produced in Y.

  
• • Faraday concluded that although a steady magnetic field produces no current, a changing magnetic field can produce an electric current. • Such a current is called an induced current.
• We therefore say that an induced current is produced by a changing magnetic field. The corresponding emf required to cause this current is called an induced emf
• Induced emf is an electromotive force resulting from the motion of a conductor through a magnetic field, or from a change in the magnetic flux that threads a conductor
• Faraday did further experiments on electromagnetic induction, as this phenomenon is called. (refer diagram) a) A current is induced when a magnet is moved toward a coil/loop. b) The induced current is opposite when the magnet is moved away from the coil/loop. c) No current is induced if the magnet does not move relative to the coil/loop.
• When the bar magnet is stationary, the galvanometer not show any deflection (no current flows in the coil).

  
• When the bar magnet is moved relatively towards the coil, the galvanometer shows a momentary deflection to the right

  
• When the bar magnet is moved relatively away from the coil, the galvanometer is seen to deflect in the opposite direction

  
• From the experiment (solenoid with magnet) there is any relative motion between the coil and the bar magnet, the current known as induced current will flow momentarily through the galvanometer. This current due to an induced e.m.f across the coil.
• Conclusion: When the magnetic field lines through a coil changes thus the induced emf will exist across the coil
• The magnitude of the induced e.m.f. depends on the speed of the relative motion where if the: v increase, induced emf increased. v decrease, induced emf decreased
• Conclusion : Therefore v is proportional to the induced emf.