Physics Demo Number: 050

Approximate Run Time: 10 min

LR Decay With Strong Spark As Stored Energy in Inductor Dissipates

Demo Description

Show LR decay of a current .

By using two ice-picks as part of the current carrying circuit, one may break the current quite abruptly and draw a substantial spark across the ice-pick points.

Scientific Principles

• LR decay of current

• Inductive circuits can store energy, which can be detected when the current is interrupted.

Equipment

• Cart [A-B] from demo(049)

• 12V cart battery (part of cart)

• Two ice-picks( contained in compound arc (9-10))

• Arc (4)

Equipment Location

• Cart [A-B]( which lives along wall at end of A and B Columns ) houses the equipment.

• Arcs (4) and (9-10) are in the Kit on the middle shelf of Cart [A-B].

Instructions

By using the ballast transformer from the previous (#049) demonstration , one may vividly show LR decay of current with an attendant high voltage spark discharge of the stored energy in the inductor.

Remove the safety stoppers from the points of the ice picks.

Slide the shafts of the two picks continuously against each other for a few seconds and then rapidly move one shaft off the tip of the other to see a very bright discharge.

One must be careful to hold only to the wood handles of the picks to avoid a nasty high voltage shock.

Note that compound arc (9-10) , aka Tag (9-10) , has been specially constructed so that it is open circuited until the two ice-pick shafts touch each other.

Writeup created by David A. Burba

Copyright © 2013, Vanderbilt University.   All Rights Reserved.