Relate Lenz’s Law to the law of conservation of energy and apply the law of conservation of energy

DC Motor                                                          

  • Lenz’s law states that induced current opposes the changing magnetic field that created it.
  • The current going backwards (back EMF) conserves energy.
  • As work needs to be done produce current against the back emf.
  • Opposes motion of motors (otherwise this would produce free energy)

Back EMF ensures that constant energy needs to be provided to do work in a DC motor.

  • Magnetic field is applied to a portion of the metal disks
  • Due to changing flux in different areas of rotating disks , eddy currents develop as shown in the picture.
  • The eddy currents prevent rotation of the disk to reduce changing magnetic flux of the metal disk areas.
  • Thus unless external force is applied, the disks stop rotating.

Extract from Physics Stage 6 Syllabus © 2017 NSW Education Standards Authority (NESA)