Efficiency is a concept associated with work done by machines.In Physics this concept is defined as the quotient between the useful work done by the machine in a given interval of time and the total work invested in the machine during the same amount of time. The following visual summarises what efficiency is.

In this teaching unit you will learn: To describe qualitatively the phenomena of electrification, electrostatic attraction and repulsion and to introduce the concepts of electric charge, insulators and conductors. To justify Coulomb's law and use it to calculate the force exerted by one or two charged particles on another. To intensity and calculate its value in the case of one or two charged particles. To describe the electric field using force lines. To justify the concepts of potential ele...