RESISTANCE - The opposition to flow of charge through a material, expressed in ohms (). Resistance is similar in many respects to mechanical friction. The resistance of a wire depends on its material, length, thickness and temperature.

RT = Total Resistance

Series circuit RT=R1+R2+R3+... etc.

Parallel circuit RT=(R1xR2)/(R1+R2) or 1/[(1/R1)+(1/R2)+(1/R3)+(.

Resistivity of

various materials (higher =

more resistance)

Silver 9.9

Copper 10.37

Gold 14.7

Aluminum 17.0

Tungsten 33.0

Nickel 47.0

Iron 74.0

Carbon 21,000

impedance

The resistance and reactance a wire or component offers to a change in current as the current runs down the length of the wire, also measured in ohms.

Thus the difference is as the current changes the resistance changes and this is expressed as ohms but is impedence.

Hope this helps Dave