Physics Demo Number: 035

Approximate Run Time: 15 min

Forces Between Two Parallel Current-Carrying Wires

Demo Description

Current is sent through two sets of parallel hanging wires using a large Variac.

The middle photo shows the state of the wires with no current flowing through them.

The bottom left photo shows the "current-on" state of the two sets of wires.

Notice that the longer set is now sucked together and the shorter set is pushed apart.

Of necessity, from viewing the hook up to the power supply, the shorter set of wires must have their currents anti-parallel. Noting that the shorter set are indeed pushing each other apart, means that internal wiring must have the currents parallel in the longer set of wires, since the longer set of wires are indeed pulling each  other together.

Scientific Principles

• Force of attraction between two parallel currents

• Force of repulsion between two anti-parallel currents

Equipment

• Variac

• Kit (035)

Equipment Location

• The Variac and Kit (035) are both on [B-3-2]

Instructions

The pictures show apparatus for demonstrating forces between two current carrying wires.

For large impulsive currents, the large Variac must be ONLY quickly pulsed up to about the 20% mark and back down IMMEDIATELY or the fuse will blow. For steady state currents the Variac may be set on the10% mark for up to a minute.

The two sets of wires need to be televised for optimum visibility in large lecture halls. However this new plexiglass modification of the hanging mechanism is about ideal for using the document camera or overhead projector instead of a video camera.

The forces of repulsion and attraction are quite small for realizable , non-destructive currents.

This necessitates extreme attention to the exact electro-mechanical hookup and choice of the wires and power supply.

Notes:

1) The two sets of hanging wires are permanently dedicated to this apparatus and their exact state of electro-mechanical positioning. KINDLY do not alter the wires in any way.  If you have a need for wiring in another location , do not steal from this apparatus, PLEASE !

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Setup for using  the document camera is seen in the following two pictures.

Writeup created by David A.Burba

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