2 If coils of copper and Eureka wires of the same gauge can be prepared so that they have equal resistances, the effect is very striking. However, this would then lose its value as an open investigation.
3 Students should come to understand that the resistance of a wire depends on its length, its cross sectional area, and the material out of which it is made. With some students you could go further and introduce the concept of resistivity ρ, through the relationship R = ρ l / A where R = resistance, ρ = resistivity, l = length and A = cross-sectional area.
4 This may also be an opportunity for a large scale demonstration of the effect by the teacher. But note: if the current is too large, the voltage of the cells will fall due to their internal resistance. For this reason, it is important to keep the current very low - copper wire is effectively a short.
5 How Science Works extension: This experiment can be used as a more open-ended investigation. Students can select the variables, the ranges of results and the equipment used. The amount of guidance will depend greatly upon the teaching group. Investigating the effect of length on resistance is common but some students may wish to investigate the effect of the thickness of wire. In either case, different wires should be made of the same material. Students may need to know the conversion between SWG (standard wire gauge) and wire diameter/radius.
Students will find it easier to measure at a prescribed length if they tape the wire to a metre rule with insulating tape and make connections with flying leads rather than crocodile clips.
This experiment was safety-checked in August 2007
Ans: The resistance of a wire depends upon the various factors:
1. It directly proportional to its length L.
2. It is inversely proportional to its area of cross section A.
3. It depends upon the nature of the material.
4. It also depends upon the temperature of the wire.
There are three main factors that affect the conductivity or resistivity of a material: