1) It is well known that the resistance of a material varies with temperature. Variable which represents this variability of resistance is defined as temperature coefficient of resistance.

The resistance-change factor per degree Celsius of temperature change is called the temperature coefficient of resistance. This factor is represented by the Greek lower-case letter “alpha” (α). A positive coefficient for a material means that its resistance increases with an increase in temperature where as a negative coefficient means that resistance decreases with an increase in temperature.

The electrical resistance of conductors such as silver, copper, gold, aluminum etc., depends upon collusion process of electrons with in material. As the temperature increase, this electron collusion process becomes faster, which results in increased resistance with rise in temperature of conductor. This property of materials which increase the kinetic energy of molecules is represented as temperature coefficient of resistance.

2) The emf (electromotive force) is the the potential difference between the terminals of a battery when no current is flowing through an external circuit when the circuit is open.Potential difference is the voltage across the terminals of the battery when the current is being drawn from it to an external.