Lectures on Physics has been derived from Benjamin Crowell's Light and Matter series of free introductory textbooks on physics. See the editorial for more information.... 
Home Electricity Circuits Examples Resistance and Cross Sectional Area  
Search the VIAS Library  Index  
Dependence of resistance on crosssectional area
We have alluded briefly to the fact that an object's electrical resistance depends on its size and shape, but now we are ready to begin making more mathematical statements about it. As suggested by the figure, increasing a resistors's crosssectional area is equivalent to adding more resistors in parallel, which will lead to an overall decrease in resistance. Any real resistor with straight, parallel sides can be sliced up into a large number of pieces, each with crosssectional area of, say, 1 μm^{2}. The number, N, of such slices is proportional to the total cross sectional area of the resistor, and by application of the result of the previous example we therefore find that the resistance of an object is inversely proportional to its crosssectional area. An analogous relationship holds for water pipes, which is why highflow trunk lines have to have large crosssectional areas. To make lots of water (current) flow through a skinny pipe, we'd need an impractically large pressure (voltage) difference.


Home Electricity Circuits Examples Resistance and Cross Sectional Area 