Physics Demo Number: 131
Approximate
Run Time: 5 min
Overhead Projector Devices for Showing Magnetic Fields of Current Carrying Wires
Demo Description
A simple overhead projector device is used to show the magnetic field lines associated with a coil of wire when it is made to momentarily carry a high current.
Scientific Principles
-
Currents generate magnetic fields.
Equipment
-
A rigid wire has been bent into a 9 turn extended -solenoid coil by threading the wire through 20 holes drilled in a transparent board designed to sit on the stage of an overhead projector.
-
A 6 volt rechargeable battery for momentary surges of DC current in the wire of the coil projector mount.
-
Shaker of Iron Filings to show field lines.
Equipment Location
-
Kit (131) on [B-1-5].
Instructions
The
picture shows the old overhead projector devices from Kit (131) for
showing the direction of the magnetic field associated with a long
straight wire (left) and a coil of wire (right) when they have a 6V
battery supplying current through them. Note that these devices depend
on small compass needles aligning correctly to show the direction of
the magnetic field lines at their location.
--------------------------------------------------------------------------------------------------------
NEW: Forget the pictured devices above.
Abandon the little compasses altogether !!
Instead of trying to ascertain field directions at specific points with the troublesome compasses and 6-V lantern batteries, do the following procedure.
The following photo depicts the best way to show the field lines around the coil and the wire, thanks to an astute observation of Professor S. Hutson about the 6-V lantern batteries used for current sources prior to 13 Feb 2007.
The photo shows using a six volt rechargeable battery as the new source of current.
Note that this new procedure allows tapping the plate (which has been sprinkled with iron filings powder ) while a momentary current flows through the wire , to see the same sort of representation of the field lines as displayed for a permanent bar magnet.
The photo also shows the new solenoid coil for using on an overhead projector with the 6 volt battery supplying momentary current.
Showing the field lines of only the solenoid is being used (without worrying about showing the field lines of a single straight wire).