Humans were essentially hunters and gatherers. They had developed the use of fire. B â¦ ut they did not live a settled existence, instead following herds of animals on their migrations which were their primary source of food. Men were the hunters and responsible for the group's primary food source.
Emf - is the amount of energy of any form that is changed into electrical energy per coulomb of charge. pd - is the amount of electrical energy that is changed into other forms of energy per coulomb of charge. Sources of emf: Cell, battery (a combination of cells), solar cell, generator, dynamo, thermocouple.
In order to provide a potential difference, or electro-motive force (EMF) a store of energy is required. One such method is a battery or cell. The common usages of the term battery is any device that converts chemical energy into electrical energy. However, strictly speaking, the term battery is used when several electrical cells are connected together to provide a source of a potential difference in a circuit.