Magnetic field due to a long close-wound coil
Iron filings show that a long, closely wound current-carrying coil behaves just like a bar magnet.
Apparatus and materials
Copper wire, PVC-covered, 100 cm with bare ends
Plotting compass (optional)
Health & Safety and Technical notes
Warn the class to keep fingers away from eyes. Iron filings inadvertently carried to the eyes can damage the cornea.
a Make a coil of twenty or thirty turns by winding the wire around a pencil. (Leave enough wire free at either end to make connections to the power supply.) The coils should be wound firmly and closely on the pencil.
b Lay the coil on the cardboard and sprinkle iron filings onto the board.
c Switch on the current, tap the board, and observe the pattern.
d Try using a plotting compass after you have tried the iron filings. Investigate what happens if the connections are reversed.
1 The long, closely wound coil behaves just like a bar magnet.
2 The direction of the magnetic field reverses when the current is reversed.
This experiment was safety-checked in April 2006