Electromotive force is defined as the electric potential produced by the conversion of other forms of energy such as chemical or magnetic into electrical energy.
Alternating EMF is produced when an AC generator is made to generate current.
The EMF will oscillate between its highest value and lowest value and the direction of the current also changes with respect to it.
An AC generator produces EMF by rotating a coil made of conductors in the presence of an electric field.
The amplitude of the EMF thus generated will depend upon the material the coil of the generator is made of.
Higher the conductivity of the material, the higher the amplitude of EMF produced.
Thus, the amplitude of the alternating EMF depends on the material with which the coil of the generator is made of.