Higher tier: resistance and area of cross-section
A second experiment can be carried out to investigate experimentally how the resistance of a metallic conductor at constant temperature depends on the area of cross section.
The above experiment is repeated but with six, equal lengths of constantan wire, of different thickness.
Record voltage, current and diameter of the wire, d.
Calculate resistance and cross section area, A, in mm2 (A = \(\frac {{\pi }d^2}{4}\)).
Plot a graph of resistance, R, in 惟 on the y-axis against cross section area, A, in mm2 on the x-axis.
Draw the line of best fit.
We can see from the graph that as the cross section area, A, increases, the resistance, R, decreases.
A thicker wire has a smaller resistance than a thin wire.
A more detailed investigation shows that resistance and cross section area are inversely proportional.
If you double the cross section area you half the resistance of the wire.
A final experiment can be carried out to investigate experimentally how the resistance of a metallic conductor at constant temperature depends on the material of the conductor.
The experiment is repeated again but with six, equal lengths and thicknesses of wire of different materials.
Record voltage, current and calculate resistance.
A comparison of results in the table shows that wires of different material have different resistance.
Key points (Higher tier only)
The resistance of a metallic conductor at constant temperature depends on:
- The length of the conductor - resistance is directly proportional to length.
- The cross section area - resistance is inversely proportional to cross section area.
- The material of the conductor.
Resistance increases as:
- the length of the wire increases;
- the thickness of the wire decreases.
An electric current flows when free electrons move in one direction through a conductor, such as a metal wire.
The moving electrons can collide with the ions in the metal.
This makes it more difficult for the current to flow, and causes resistance.
The resistance of a long wire is greater than the resistance of a short wire because electrons collide with more ions as they pass through.
Resistance and wire length are Relationship between two variables where one variable is equal to a constant multiplying the other variable. Variables are plotted as a straight line though the origin..
The resistance of a thin wire is greater than the resistance of a thick wire because a thin wire has fewer gaps for the free electrons to pass through.
Resistance and the area of cross section of a wire are Two values are said to be inversely proportional, when one amount increases and the other amount decreases..