Science Buddies: "Ask an Expert"

My son is working on a Electromagnet.
He has it working but when the copper wire is unclipped from the battery it is still magnetized. He was trying to hook it to a switch so when it was off it would stop working but it still was magnetized. He thought something was wrong with his switch so he disconnected the battery.With no power should it lose its magnetic power

Please help us!
Jeremy

Electromagnetism is nothing but fascinating!

No, removing the electric current will not zero the magnetic force. It will be reduced but not fully suppressed. There is a remnant magnetic field that is typically removed by cycling the magnet through a degauss procedure.


See http://hyperphysics.phy-astr.gsu.edu/hb ... /hyst.html

keyword for further reading. Hysteresis, degauss.

In practice, if you need to get to zero field, you will need to apply a current of the opposite polarity (reverse the battery cables) but you would need to be able to control the amount of current through the magnet by using a variable resistor.

Hope this helps, let us know if you have follow up questions.