310102c Characteristics of Conductors Mar 2025 (TF)

Instrument Technician

Characteristics of Conductors

• Course Code: 310102c

Objectives

• The student will be able to:

  • Describe the factors affecting resistance.

  • Calculate the resistance of a conductor of specific dimensions.

  • Describe the electrical properties of materials.

4 Factors Affecting Resistance

1. Length of Conductor

   • Longer conductors increase resistance.

2. Cross-Sectional Area of Conductor

   • Larger cross-sectional areas reduce resistance.

3. Type of Conductor Material

   • Different materials (like copper and aluminum) have varying resistivities.

4. Temperature of Conductor

   • Temperature affects the resistance; generally, resistance increases with temperature.

American Wire Gauge (AWG) Table

• There are 44 gauge sizes, ranging from #4/0 AWG (largest cross-sectional area) to #36 AWG (smallest).

• Larger AWG numbers correspond to smaller cross-sectional areas.

American Wire Gauge (AWG) Sizing

• The larger AWG numbers arise from a history of wire sizing.

  • It pertains to the number of times wire has been pulled through smaller dies during manufacturing.

  • Initially, #1 AWG was considered the largest, later leading to sizes #0 (1/0), #00 (2/0), #000 (3/0), and #0000 (4/0) AWG.

Conductor Resistance

• Materials:

  • Copper (Cu) primarily used, but aluminum is also common.

• Resistance can be calculated through:

  1. Type of material.

  2. Length of wire.

  3. Cross-sectional area.

  4. Temperature.

• 
  

  
  

  Formula:[ R = \frac{\rho L}{A} ]Where:

  • R = electrical resistance in ohms (Ω)

  • ρ = static resistivity in ohm-metres (Ω-m)

  • L = length of material in metres (m)

  • A = cross-sectional area in square metres (m²).

  • Note: Convert mm² to m² by multiplying by 10^{-6}.

Resistivity Values

• At 20˚C:

  • Copper: ρ = 17.2 x 10^{-9} Ω•m

  • Aluminum: ρ = 28.3 x 10^{-9} Ω•m

• Resistance Calculation Example:

  • For 100m of copper wire with 1.039 X 10^{-6} m² cross-sectional area: [ R = \frac{17.24 x 10^{-9} \text{Ω•m} \times 100 \text{m}}{1.039 X 10^{-6} \text{m}²} = 1.66Ω ]

Temperature Coefficients of Common Electrical Materials

• Material and Coefficient (per °C change):

  • Copper: α = 0.0039

  • Aluminum: α = 0.0039

  • Tungsten: α = 0.0045

  • Nichrome II: α = 0.00016

  • Germanium: α = -0.05

• Positive coefficients mean resistance increases with temperature; negative means decreases.

Resistance Calculations Involving Temperature

• Formula: [ R_2 = R_1[1 + \alpha(t_2 - t_1)] ]

• Example Calculation:

  • Given R = 3.27Ω at 20°C; calculate resistance at 350°C (α = 0.0039).

Example Resistance Calculation (Copper Wire)

• Given: R = 8Ω at 20°C; calculate at 80°C (α = 3.93 X 10^{-3}). [ R_2 = 8Ω[1 + 3.93 x 10^{-3}(80 - 20)] = 9.89Ω ]

Conductors, Insulators, and Semi-conductors

• Conductors: 1-3 electrons in valence shell; good for electron transfer.

• Insulators: 5+ electrons in valence shell; restrict electron flow.

• Semi-conductors: 4 electrons in valence shell; can act as conductors or insulators.

Assignments

• Complete Self-Test 310102c

• Complete Electrical Assignment 3