RESISTANCE Resistance Electrical resistance is the characteristic of

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 1. Type of material Some substances resist electron flow more than others. 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 glass 0. 46 1010 to 1014

Factors Affecting Resistance 2. Cross-sectional area The thinner a wire, the greater will be its resistance. Gauge Diameter (mm) Resistance (x 10 -3Ω/m) 0 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 3. Length The longer a wire, the greater will be its resistance. more resistance less resistance

Factors Affecting Resistance 4. 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.