Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications!

This is an AMP page - Open full page! for all features.

• the most efficient way to navigate the Engineering ToolBox!

# Resistance vs. Resistivity

Electrical resistance of an electrical conductor depends on

• the length of the conductor
• the material of the conductor
• the temperature of the material
• the cross-sectional area of the conductor

and can be expressed as

R = ρ L / A               (1)

where

R = resistance of the conductor (ohms, Ω)

ρ = resistivity of the conductor material (ohm metre, Ω m)

L = length of conductor (m)

A = cross-sectional area of conductor (m2)

### Resistivity of some Common Conductors

• Aluminum: 2.65 x 10-8 Ω m (0.0265 μΩ m)
• Carbon: 10 x 10-8 Ω m (0.10 μΩ m)
• Copper: 1.724 x 10-8 Ω m (0.0174 μΩ m)
• Iron: 10 x 10-8 Ω m (0.1 μΩ m)
• Silver: 1.6 x 10-8 Ω m (0.0265 μΩ m)

Note that resistivity depends on temperature . The values above are for temperatures 20 oC .

.

### Resistivity of some Common Insulators

• bakelite: 1 x 1012 Ω m
• glass: 1 x 1010 - 1 x 1011 Ω m
• marble: 1 x 108 Ω m
• mica: 0.9 x 1013 Ω m
• paraffin oil: 1 x 1016 Ω m
• paraffin wax (pure) : 1 x 1016 Ω m
• plexiglass: 1 x 1013 Ω m
• polystyrene: 1 x 1014 Ω m
• porcelain: 1 x 1012 Ω m
• pressed amber: 1 x 1016 Ω m
• vulcanite: 1 x 1014 Ω m
• water, distilled: 1 x 1010 Ω m

Note that good conductors of electricity have low resistivity and good insulators have high resistivity.

### Example - Resistance of a Conductor

The resistance of 10 meter gauge 17 copper wire with cross sectional area 1.04 mm2 can be calculated as

R = (1.7 x 10-8 Ω m) (10 m) / ((1.04 mm2)(10-6 m2/mm2))

= 0.16 Ω

### Example - Cross-sectional area and Resistance

The copper wire above is reduced to gauge 24 and cross-sectional area 0.205 mm 2. The increase in resistance can be calculated to

R = (1.7 x 10-8 Ω m) (10 m) / ((0.205 mm2)(10-6 m2/mm2))

= 0.83 Ω

### Convert between Electrical Resistivity Units

• 1 Ω m = 0.001 kΩ m = 102 Ω cm = 39.37 Ω inch = 3.28 Ω foot

### Resistivity Compared to Copper

• Aluminum (pure): 1.6
• Brass: 3.7-4.9
• Chromium: 1.8
• Copper (hard-drawn): 1.03
• Copper (annealed): 1.00
• Gold: 1.4
• iron (pure): 5.68
• Nickel: 5.1
• Phosphor Bronze: 2.8-5.4
• Silver: 0.94
• Steel: 7.6-12.7
• Tin: 6.7
• Zinc: 3.4

## Related Topics

### • Electrical

Electrical engineering with units, amps and electrical wiring. Wire gauges, electrical formulas, motors and more.

## Related Documents

### Aluminum and Copper Wires - Electrical Resistance vs. Cross-Sectional Area

Electrical resistance in plain copper or aluminum wires.

### Aluminum Conductor Characteristics

Characteristics of all-aluminum conductors (AAC).

### Beams Natural Vibration Frequency

Estimate structures natural vibration frequency.

### Electric Wire - Resistance

Electric resistance in wire made of Copper, Aluminum, Brass, Constantan, Nichrome, Platinum, Silver or Tungsten.

### Electrical Conductivity - Elements and other Materials

Electric conductance is the ability of a element to conduct an electric current.

### Electrical Motors - Maximum Cable Size and Length vs. Power

Maximum electrical motor cable length vs. power.

### Electrical Parallel Circuits

Resistance, voltage and current in electrical parallel circuits.

### Kirchhoff's Voltage and Current Laws

Kirchhoff's current and voltage laws.

### Nickel-Chromium Heater Wire - Temperature Rise vs. Amps

Electric resistance vs. temperature rise for Nickel-Chromium electrical heater wire.

### Resistivity and Conductivity - Temperature Coefficients Common Materials

Resistivity, conductivity and temperature coefficients for common materials like silver, gold, platinum, iron and more..

### Voltage Dividers - Online Calculator

Output voltage potential divider.

## Search Engineering ToolBox

• the most efficient way to navigate the Engineering ToolBox!

## SketchUp Extension - Online 3D modeling!

Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your Sketchup model with the Engineering ToolBox - SketchUp Extension - enabled for use with the amazing, fun and free SketchUp Make and SketchUp Pro . Add the Engineering ToolBox extension to your SketchUp from the Sketchup Extension Warehouse!