Physics

Home > Physics > Core > Motors and generators > Motors and generators: 5. AC motors

DOCTYPE

9.3 Motors and generators: 5. AC motors

Syllabus reference (October 2002 version)
5. Motors are used in industries and the home usually to convert electrical energy into more useful forms of energy
Students learn to: Students:

Extract from Physics Stage 6 Syllabus (Amended October 2002). © Board of Studies, NSW.
[Edit: 30 June 09]

Go To Top

perform an investigation to demonstrate the principle of an AC induction motor

Sample procedure

One of the simplest and safest ways to demonstrate the principle of an AC induction motor is to show how an aluminium disc that is free to rotate will rotate when a permanent magnet is rotated close to it.

Cut the bottom of an aluminium drink can so that you end up with a round disc. Attach a long fine thread to the centre of the disc so that the disc is balanced and can hang horizontally.  Attach the free end of the thread to a high support, such as the edge of a table, so that the disc is hanging freely.

Attach a bar magnet firmly to the end of a pencil so that it forms a “T” with the pencil. Mount the pencil vertically in the chuck of a hand drill so that the magnet is close beneath the suspended aluminium disc. Rotate the hand drill to make the magnet spin in one direction.

Hand drill, Magnet and suspended aluminium disc

Replace the permanent magnet with an unmagnetised piece of iron or other non-magnetic material. Alternatively, replace the aluminium disc with discs of other metallic and non-metallic materials. Rotate the apparatus at different speeds and in each direction. Systematically observe and record the effects of any changes you make to the variables in the procedure.

Explanation of the model

In this model the rotating magnetic field of the bar magnet induces a current in the aluminium disc that produces a magnetic field opposing that of the bar magnet. The interaction between the two magnetic fields causes the aluminium disc to spin, chasing the rotating permanent magnet.

Go To Top

describe the main features of an AC electric motor

A Squirrel Cage induction rotor
Go To Top

gather, process and analyse information to identify some of the energy transfers and transformations involving the conversion of electrical energy into more useful forms in the home and industry

Note

An energy transfer occurs when energy in one form moves from one object or location to another object or location as the same form of energy, for example, heat transferred by conduction from the electric heating element to the water in a domestic hot water system.

An energy transformation occurs when energy is changed from one form to another form within an appliance, for example, electrical energy changed into useful rotational kinetic energy in a food processor. Many energy transformations are not useful, as various forms of energy are converted into waste heat.

Sample information

Electrical energy is transferred from the primary coil to the secondary coil in a transformer. This type of energy transfer occurs in plug-in voltage adaptors for many small home appliances, such as CD players and mobile phone rechargers, as well as industrial applications such as welders. Electrical energy is transferred by induction from the stator to the rotor in an induction motor, both in the home and in industry.

Electrical energy is transformed into a range of other useful types of energy both in the home and in industry:

In the home In industry
Electrical energy is transformed into radiant energy as:
  • light in light globes
  • heat in toaster and kettle
  • microwaves in microwave oven
  • radio waves in cordless phone
Electrical energy is transformed into radiant energy as:
  • X-rays in medical imaging
  • light in laser circuit printing
  • heat in induction ovens
  • microwaves in wood curing
  • radio waves in communication
Electrical energy is transformed into mechanical energy as:
  • rotation in food blender motor
  • vibration in television speaker
Electrical energy is transformed into mechanical energy as:
  • rotation in industrial motors
  • vibration in television speaker
  • kinetic energy and gravitational potential energy in fun park rides
Electrical energy is transformed into chemical energy in recharging rechargeable batteries Electrical energy is transformed into chemical energy in the electroplating process

Sample analysis

Electrical energy is transformed into heat energy, both in the home and in industry, when large electric currents flow through metals with high resistance. In electric kettles and toasters, current from the mains causes heating in a high-resistance element. In an induction oven, changing magnetic fields cause eddy currents to flow in the metal parts which become hot because of their electrical resistance.

Go To Top

Neals logo | Copyright | Disclaimer | Contact Us | Help