Resistance Wires (5D10.20)

Description:

One board containing five wires of different lengths, areas, and materials. Each of the wires is hooked in turn across a battery and the current through the wire is shown on a large meter. The dependence of resistance on length, area, and composition of the wire can be shown. See also Ohm's Law (5F10.10) and Series and Parallel Resistance (5F20.55).

Procedure or Operation Notes:

From top to bottom, the wires are:

Wire Material Diameter Length Resistance
A Constantan (1) 0.02" [0.5mm] 15 feet [4.6m] 11Ω
B Evanohm (2) 0.04" [1mm] 15 feet [4.6m] 7.5Ω
C Evanohm 0.02" [0.5mm] 15 feet [4.6m] 30Ω
D Evanohm 0.02" [0.5mm] 7.5 feet [2.3m] 15Ω
E Evanohm 0.02" [0.5mm] 3.75 feet [1.1m] 7.5Ω

(1) Constantan: 55% Copper, 45% Nickel. Resistivity: ρ = 5x10-7 Ω·m.
(2) Evanohm: 74.5% Nickel, 20% Chromium, 2.75% Aluminum, 2.75% Copper. Resistivity: ρ = 1.33x10-6 Ω·m.

Wire Resistance: R = Resistivity · Length / Area

The right side of all five wires are connected together. Move the single lead between the left side of the wires to compare their resistances.

Compare all wires to wire C.
(Note that The battery was not fully charged when these pictures were taken. The battery voltage doesn't usually drop as much under load like it did here.)

Wire C: Current = 0.4A.
Wire D: Current = 0.8A.
Wire E: Current = 1.6A.
Wire B: Current = 1.6A. Note the wire diameter, cross sectional area, and length.
Wire A: Current = 1.1A. Note that wire A is a different material than wires B through E.

References, Comments, or Footnotes:

Also see the following demos:

1) Ohm's Law (5F10.10).

2) Series and Parallel Resistance (5F20.55).