Define 'emf' in electricity.

'Emf,' or electromotive force, refers to the energy provided per unit charge by a source of electrical energy, such as a battery or a generator. This definition highlights the role of emf as the driving force behind electron flow in a circuit, effectively establishing the potential difference that causes current to move. It indicates how much energy is supplied to each coulomb of charge that passes through the source.

The concept of emf is fundamental in understanding how electrical circuits operate. It encompasses not just the voltage, but also the intrinsic abilities of the source to convert other forms of energy (mechanical, chemical, etc.) into electrical energy, thereby raising the energy levels of the charges it influences.

While energy produced per unit of voltage in a circuit, energy consumed by electrical devices, and energy lost during the transmission of electricity relate to different aspects of electrical systems, they do not accurately capture the definition of emf itself. Each of these options refers to a specific context or effect in electrical systems without addressing the core function of emf as a measure of energy provided per charge by a source.