RESISTANCE

Resistance Electrical resistance is the characteristic of a material that slows electron flow. Resistance is represented by the symbol R. The unit of resistance is the ohm (Ω).

Resistance

Voltage & Current

Resistance

Factors Affecting Resistance Material Resistivity (ρ) (Ω•m) silver 1.6 x 10-8 copper 1.7 x 10-8 aluminum 2.7 x 10-8 tungsten 5.6 x 10-8 Nichrome 100 x 10-8 carbon 3500 x 10-8 germanium 0.46 glass 1010 to 1014 Type of material Some substances resist electron flow more than others.

Factors Affecting Resistance 2. Cross-sectional area The thinner a wire, the greater will be its resistance. Gauge Diameter (mm) Resistance (x10-3Ω/m) 9.35 0.31 10 2.59 2.20 14 1.63 8.54 18 1.02 21.90 22 0.64 51.70 The thickness of the wire is called its “gauge”. As the gauge of the wire increases, the wire becomes thinner and the resistance increases.

Factors Affecting Resistance 2. Cross-sectional area The thicker a wire, the lower will be its resistance.

Factors Affecting Resistance Length The longer a wire, the greater will be its resistance. more resistance less resistance

Factors Affecting Resistance Temperature The warmer the wire, the greater will be its resistance. greater resistance less resistance

Resistors A resistor is a device that reduces the flow of electric current.