Idea 4of 4Builds onOnly change inducesThe total never changesSpin it
The bill for free energy
The induced current makes its own field. Which way?
Today you'll discover
- which way the induced current points
- why it could not point the other way
- why a magnet falls slowly down a copper pipe
Think firstThe magnet moves in. The induced current makes a field
The induced current makes its own field. Does it pull the magnet in, or push it back?
Decide first, then press Next. Watch which way the coil's arrows point as the magnet moves.
A magnet, a coil and a meter, with arrowheads on the coil's wire for the induced current. After a prediction, the magnet moves in and the arrows show a current whose field opposes it; the magnet moves out and the arrows reverse, pulling it back. The last step asks why a magnet falls slowly down a copper pipe.
See the whole ideathe big idea and the key word, in one place
The big idea
The induced current always opposes the change that made it.
Easy to get wrongA generator is hard to turn when it is powering something. That resistance is Lenz's law presenting the bill: the light's energy is the work supplied against it.
Key word
- Lenz's law
- an induced current flows in the direction that opposes the change producing it; a consequence of energy conservation
About this modelOnly CHANGE induces: a still magnet, however strong, induces nothing. Faster change, bigger swing.
Only CHANGE induces: a still magnet, however strong, induces nothing. Faster change, bigger swing.
Ready to use it?
- Give the direction of an induced current's effect for a described change, using Lenz's law.