Demos: 5B-01 Ohm's Law Board

Three wires of the same length are attached to a display board. One wire is Nickel, having a diameter of 0.01 in. The other two wires are Nichrome, with diameters 0.01 in and 0.015 in, respectively. The wires are mounted on the display board such that current and voltage measurements can be compared between the wires and at defined points along each wire.

Directions: Power is supplied to the circuit by means of a 12V battery. Connect the ammeter leads to the two ends of the wire, respectively. This sets up a current in the wire. Then use the voltmeter leads to tap the voltage at various points along the wire. The ammeter and voltmeter readings are projected from the overhead.

Suggestions for Presentation: Although this is called an Ohm’s Law Board, it might be well to address the issue of what Ohm’s Law means. If your are simply using the relationship V = IR, this is not technically Ohm’s Law, rather a relationship that defines resistance, R = V/I. Ohm’s Law is restricted to a linear relationship between V and I.

To optimize the effect of this demo, use combinations of wire type and wire length. To test whether Ohm’s Law applies here, clip one ammeter lead at the center of the wire. This should reduce the resistance to one-half and with the voltage the same, the current should be twice as much. Other combinations can be used to test these relationships.


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Last Updated: May 9, 2016 11:44 AM