Rotor Sorts Metal Scrap

In the picture

1. 1Spinning magnetic rotor
2. 2Aluminium fragment arcing forward
3. 3Heavier metal piece falling straight down
4. 4Conveyor belt dropping mixed scrap

Examples

• Recycling plants use this to sort aluminium cans from steel cans.
• Some airport security scanners use changing magnetic fields near metal objects.

Quiz: Rotor Sorts Metal Scrap (Age 15)

1. 1

   Why can a spinning magnetic rotor push aluminium even though aluminium is not magnetic?

   • The moving magnet induces electric currents in the aluminium, and those currents create a repelling force.
   • The magnet makes the aluminium permanently magnetic, so it sticks to the rotor.
   • The rotor gives the aluminium a static electric charge, so it is repelled.
2. 2

   In this separation process, what usually happens to the heavier metal pieces that are not pushed like aluminium?

   • They are pulled upward and carried away by the rotor.
   • They fall straight down because the eddy-current force does not push them forward as strongly.
   • They move forward with the aluminium because every metal is pushed equally.
3. 3

   What condition is needed for eddy currents to be created inside a piece of aluminium?

   • The aluminium must already contain a permanent magnet.
   • The aluminium must be connected to an electric battery.
   • The aluminium must be in a changing magnetic field.

The answers, each with its explanation, are in the app. This lesson has left the free week, so its quiz is part of the subscription.