Im electrical engineer so i guess it was only matter of time before i explored this forum. Here I describe an explanation for why electricity flows in
a circuit. The talk explains the concepts of Voltage, Electric Current and Resistance in a electric circuit.
Voltage is an electrical form of pressure and to understand this concept in the easiest of way is done by
considering its analogy to a fluid system. A simple form of fluid system is found in a rainwater tank. The Pressure inside the tank is greater than
the ambient atmospheric pressure surrounding the tank. To release water from the tank into the external environment is controlled by opening a tap on
the tank. The flow of water in this manner is analogous to the flow of current. The current flow is commonly referred in everyday terms as
The flow of electricity is an effect caused by electrical pressure of voltage. To increase the magnitude effect of the flow in electricity (electric
current) requires increasing the voltage pressure. The analogy in the fluid system for this is where a tank reservoir is filled with a high fluild
level; and possess a greater head of pressure than if the tank level is low.
In a water fluid system the tank pressure is the driving source for the force which pushes the water fluid out of the tap when opened. In the same
characteristic manner for an electrical system the electric current flows from a point of high voltage potential to one of low voltage potential in a
The analogy of the water fluid system reveals that electric current is flowing/moving in a direction determined by the fall/drop in voltage
The use of the term Voltage potential is interchangeable with terms Voltage Gradient and Voltage differential and Voltage drop.
The units of Volts are Electro-motive force. Electro simply means electrical energy. The terms motive indicates motion; and force is an effect caused
by pressure of voltage as explained in the analogy above. Therefore think of Volts as electrical pressure.
The flow of electricity (electric) current cause by the electrical pressure of the voltage is referred to as in its units of measurement are amperes.
The basic relation ship between Voltage and Current is defined in what is called Ohms law. Mathematically Ohms law defines Voltage = Current x
Resistance ( V = IxR). The (x) symbol is a mathematical multiplier like 2 x 2 = 4 for example.
To explain Resistance I will go back to the analogy to a fluid system and a rainwater tank. Imagine now that a hose is connected to the outlet tap on
the tank. When the tap opened the water will flow from the tank via the tap and through the hose. The hose itself is physical a Resistance element in
the flow path of the fluid; in that it slows down the rate of fluids flow from the tap. Without the hose connected to the tap the water fluid flows
out of the tap at a faster rate compared to it the hose is connected.
Therefore Resistance is what limits the electric current flow for a given voltage. The implications of this constraint can be understood for the
layman in practical terms by considering the example of a fixed voltage source available from a home wall power socket. The wall socket may be used to
connect various electrical appliances. These could be a toaster, TV, computer, electric kettle or hot iron. Each of these appliances have a different
value of resistance. The lower the resistance the more current will flow through the electrical circuit within the appliance. A hot iron is the best
example as because altering the temperature control has the actual result of altering the resistance in the circuit.
This brings to attention the last term Power. Electric current flowing in a resistive element produces heat which is Power. Yes Power = Heat.
The mathematical formula for Power heat generated in a purely resistance circuit, P = V x I. I say purely because in actually reality applicances
such as TV, Washing machines and Radios will also have inductive and capacitive circuits. These I will cover in separate discussion later.
edit on 6-11-2012 by AthlonSavage because: (no reason given)