How a non-friction brake functions.
This experiment shows the formation and effect of induced eddy currents produced by metal’s moving in a stationary magnetic field.
- Three equal length pendulums with bobs made of intact, comb-shaped, and hole-dotted aluminum sheet respectively.
- Few magnets.
- Observe the motion of the intact and the comb-shaped aluminum sheets without and within a magnetic field.
- Observe the motion of the intact and the hole-dotted aluminum sheets without and within a magnetic field.
- Observe the motion of the comb-shaped and the hole-dotted aluminum sheets without and within a magnetic field.
- Why is there a resistance force to the swing of aluminum sheets in a magnetic field?
- Will the comb-shaped aluminum sheet experience the same resistance in a magnetic field?
- 1. The aluminum sheet experiences a change of magnetic flux when it swings in and out of the external magnetic field. The changing flux induces eddy currents and the currents form a magnetic field with a force against the swing direction of the metal sheet.
- 2. The slots on the comb-shaped aluminum sheet confine the induced eddy currents to many small current loops. These small currents are inadequate to induce a sufficient magnetic force to repress the motion of the aluminum sheet.
- Will the hole-dotted aluminum sheet experience a resistance force when it swings in a magnetic field? Why? At which size will the holes be sufficient to incur the effect of resistance?
- Discuss the possible circuits for the induced eddy currents on the metal sheet.
- Friction brake converts kinetic energy to thermal energy in the braking process. Where does the kinetic energy go in an Eddy Current Brake?
- Discuss and estimate the resistance force magnetically induced by conductors like flying airplanes or rockets cutting the Earth’s magnetic field.
- Why Eddy Current Brakes are not widely applied in the design of vehicles?
About the Experiment
Benson, H. (1995).Chapter 31 Electromagnetic Induction. University Physics. John Wiley & Sons Inc.