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Units of electricity
Volts
- Volt (V) is a SI unit, defined as the work of 1 joule (J) that must be done on a positive (+ve) charge of 1 coulomb (C).
- Voltage represented by E, current represented by I and resistance represented by R are related to each other by -
and is easilly remebered by the fact that E comes before I and I come before R.
Joule
Coulomb
A Coulomb (C) is a unit of electric charge and is related to current.
One Coulomb (C) is the electric charge moved when 1 Amp flows for 1 second (s).
Energy
Energy has joule as its unit.
Energy is a physical quantity related to the ability of a system to do work.
Energy can be kinetic, related to movement of masses, potential or in thermodynamics, internal.
Energy can be transferred or transformed, but never destroyed.
Work
- Work has joule as its unit which is also the unit for energy.
- All objects in the universe, if at rest or in motion, remain so until a force acts upon that object setting the object in motion or altering its motion.
- Work is done when energy is transferred (e.g. to an object) through the application of a force acting through a distance.
- Work done can be stored as potential energy in a variety of systems.
Such a system is an electro-chemical system e.g. electro-chemical cell, battery that stores energy as an electric potential.
Electric potential
- Most aspects of electricity can be better under stood if we view it as flowing water (see diagram)
- Electro motive force (emf) or its units, volts (V), is the driving force or push behind a flowing electric current.
- An electric potential is the term used for the electro motive force in electrochemistry where there is no current flow but a potential exists.
Ampere
- Ampere (A) is a SI unit of electric current flow.
- It is the base unit that all other electric units and is defined as the electric current flow in two infinitely long electric conductors, spaced 1 metre apart, in a vacuum, that will exert a force on each other of 2 * 10-7 Newtons (N - unit of force) per metre.
Electric current
- Electric current has the ampere (A) as its unit.
- Electric current can be a flow of electrons in a electric conductor, such as a copper wire, or a flow of ions in a solution.
- A Electric current flows when a electromotive force (emf) is applied to a complete electric circuit.
- Current represented by I, voltage represented by V and resistance represented by R are related to each other by -
and is easilly remebered by the fact that E comes before I and I come before R.
Electric resistance
- Electric resistance (R) has ohm (W) as its unit.
- Electric resistance can be defined as the electrical potential difference across a conductor to push or drive a unit current through the conductor.
In the diagram the tap closure will determine the resistance and the pressure drop across the tap the potential difference.
- Electric resistance of a wire depends on the material, cross section, length and temperature of the wire.
- Electric resistance of a solution depends on the ions and concentration of ions present and temperature of solution.
- Electrical conductance is the reciprocal or reverse of Electrical resistance
- Resistancerepresented by R, voltage represented by V and current represented by I are related to each other by -
and is easilly remebered by the fact that E comes before I and I come before R.