Page 39 - Basic Electrical Engineering

or, (1.9)

Temperature coefficient of resistance, α at 20°C and specific resistance ρ of
certain material have been shown in Table 1.1.

Table 1.1 Temperature Coefficient and Specific Resistance of Different Materials

Material Temp. coeff. of resistance α 20 Specific resistance ρ in micro
−ohm

Silver 0.004 0.016
Copper 0.0039 0.018

Aluminium 0.0036 0.028

Iron 0.005 0.100

Brass 0.0015 0.070

Lead 0.0042 0.208
Tin 0.0046 0.110

Carbon −0.00045 66.67

It is to be noted that carbon has a negative temperature coefficient of
resistance. This means, the resistance of carbon decreases with increase in
temperature.

By this time you must be wondering as to why resistance in most materials
increases with increase in temperature while resistance in some decreases

with increase in temperature.
The charged particles inside a material is in the state of vibration.

Temperature rise in most materials increases this vibration inside the material
obstructing the flow of electrons. Obstruction to the flow of electrons is

called resistance. At lower temperatures the vibration gets reduced, and hence
the resistance.

1.8 WORK, POWER, AND ENERGY