1. RESISTANCE

2. 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).

3. Resistance

4. Voltage & Current

5. Resistance

6. 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.

7. 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.

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

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

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

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