Commercial electric motors do not use (a) an electromagnet to rotate the armature (b) effectively large number of turns of conducting wire in the current-carrying coil (c) a permanent magnet to rotate the armature (d) a soft iron core on which the coil is wound

c) a permanent magnet to rotate the armature

Explanation

In an electric motor, a rectangular coil is placed in between the magnetic field and when current flows through the coil from the commutator rings, a torque acts on the coil which rotates it continuously. When the coil rotates, the shaft attached to it also rotates and thus mechanical work is done

  • . In commercial electric motors field coils are used for producing magnetic fields and not a permanent magnet.
  • These coils become magnetized when current is passed through them.
  • Field coils give a stronger, more easily shaped magnetic field than permanent magnets.
  • More the number of turns in the field coil, more the magnetic field.
  • Therefore, the suitable field coil sizes are used for various commercial purposes.

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