In a treatise published in 1827, Georg Ohm described measurements of applied voltage and current through simple electrical circuits containing various lengths of wire. In modern mathematical terms, Ohm’s law is expressed as I= V/R where I is the current in the amperes, V is the potential difference in volts and R is a circuit parameter called the resistance (measures in Ohms which is equivalent to volts per ampere).
Static Electricity
Electricity may remain static, as a fix distribution of charges, or flow, as an electric current. Static electricity builds up when changed particles move so that opposite charges accumulate in different places.
Electric Current
Electric current is a flow of charge. Metal wires conduct electricity because the electrons in metals are not tied to particular atomic nuclei and can easily be set in motion. Metals are said to be conductors of electricity and elections move through metal wire like water through a pipe.
An electrical current can be created by a gradient such as in an electrical fields or an electrical potential. Just as a change in height causes a river to run downhill, a change in electrical potential between two ends of a conducting material causes a current of charge to flow through it. This potential difference drives the current and also gives energy to the charges.
Resistance
Resistance limits the size of current by dissipating the electrical energy as heat. Effectively, resistors are conductors that slow down the passage of charge. A resistor with a high value of resistance is a poor conductor while a resistor with a low value of resistance is a good conductor.
Circuits
Electrical flows follow loops called circuits. The movement of current and energy through circuits can be described in the same way that water flows through pipes. Current is similar to flow speed, voltage to the pressure of water, and resistance to the pipe width or restrictions place in it.
According to Ohm’s law, voltage is proportional to current and resistance. Double the voltage across a circuit and you double the current flowing through it if the resistance is unchanged; to maintain the same current the resistance needs to be twice as large. Current and resistance are inversely related, so increasing the resistance slows the current.
Ohm’s law can be used throughout any circuit to calculate the voltages and currents at any point.
Sources:
Baker, Joanne (2007) 50 Physics Ideas You Really Need to Know (Quercus Publishing)
Holzner, Steve (2005) Physics for Dummies (John Wiley & Sons)
Kuhn, Karl (1996) Basic Physics: A Self-Teaching Guide (John Wiley & Sons)
