L8 - Factors Affecting Resistance

objectives

The effects of length and area

• The copper wires above have the same cross-sectional area and temperature.
• But B is twice as long as A.
• As a result, it has twice the resistance of A.
• If B were three times as long as A, it would have three times the resistance, and so on. Results like this can be summed up as follows:
• Provided other factors do not change:
• resistance ∝ length (the symbol ∝ means ‘directly proportional to’)

• The copper wires above have the same length and temperature.
• But C has twice the cross-sectional area of B.
• As a result, it has half the resistance of B.
• If C had three times the cross-sectional area of B, it would have one third of the resistance, and so on.