Welcome to practical physicsPracticle physics - practical activities designed for use in the classroom with 11 to 19 year olds
 

Magnetic field inside an open coil

Class practical

Using a plotting compass and iron filings to explore the field pattern.

Apparatus and materials

For each student group

Cylinder, wooden

Copper wire, PVC-covered, 150 cm with bare ends

Iron filings

Plotting compass

Cardboard, two slots cut into it

Power supply, low-voltage ('Westminster pattern' very-low-voltage supplies are best)

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.

Read our standard health & safety guidance

 

Procedure


Magnetic field inside an open coil

a You are going to explore the magnetic field inside a current-carrying coil of wire. Wind five spaced turns on the wooden cylinder. 

b Slide this coil off the cylinder and into slots on the board.
 
c Connect the ends up to the DC terminals of the power supply.
 
d Sprinkle iron filings onto the board, paying particular attention to the region inside the coil.
 
e Switch on the current, tap the board, and observe the pattern.
 
f Use a plotting compass to investigate the direction of the field inside and outside the coil. Investigate what happens if the current is reversed.

 

Teaching notes


This is a chance to explore the field along the centre of the coil and around some of the coils as they enter the card. Students should see that the field inside the coil is in the opposite direction to the field outside the coil.

 
This experiment was safety-checked in July 2007