Simple Theory

Simple Theory

Understanding How Electricity Works 

Electrical current is actually the movement of electrons flowing along a conductor in much the same way as water flows through a pipe. The same fundamental principles apply in the same way: the bigger the pipe, the more flow it can handle. Conversely, smaller pipes can handle small supplies. This is the principle behind the resistance.


An analogy to understanding electricity is a water pipe, where the voltage is the water pressure, the current is the flow rate, and the resistance is the size of the pipe. Current (flow rate or amps) is equal to the voltage (water pressure or Volts) divided by the resistance (size of the pipe or Ohms).

water from a hose

Amps = E / R

Current = flow rate = Amps = I

Voltage = pressure = Volts = E

Resistance = pipe size = Ohms = R


Electrical power is measured in watts. In an electrical system, power or watts (W) is equal to the voltage (V) multiplied by the current (I).

To understand power, think of taking that water pipe and pointing it at the top of an old waterwheel. To increase the power generated by the waterwheel, you can: (a) increase the pressure of the water coming out of the pipe, or (b) increase the flow rate of the water. 

Measuring Electrical Forces

When discussing electrical supply, we use many different terms to quantify the amount of available power, the amount of work it can do, the resistance of the components, and, therefore, its safe operating parameters. Here are some easy-to-understand definitions and explanations of the terminology.

Resistance: limits the conductor's ability to allow the flow of electrons, just as the friction causes losses in any pipe or ductwork. This is expressed in Ohms.

Electromotive Force: is what drives electrons along the conductor, and is expressed as voltage or volts.

Current: is the flow of electrons driven by electromotive force through a given resistance. This is expressed as amps.

Power: is the amount of work that the electrical flow can do. This is expressed as watts or kilowatts (1,000 watts).

Georg Simon Ohm was a German physicist born in Erlangen, Bavaria on March 16, 1787. Ohm started his research with the then-recently invented electric cell (invented by Italian Conte Alessandro Volta). Using equipment of his own creation, Ohm determined that the current that flows through a wire is proportional to its cross-sectional area and inversely proportional to its length. Using the results of his experiments, Ohm was able to define the fundamental relationship between voltage, current, and resistance.

These fundamental relationships are of such great importance that they represent the true beginning of electrical circuit analysis. Unfortunately, when Ohm published his findings in 1827, his ideas were dismissed by his colleagues. Ohm was forced to resign from his high school teaching position, and he lived in poverty and shame. However, his research efforts gained a lot of support outside of Germany. In 1849, Georg Simon Ohm was finally recognized for his efforts by being appointed as a professor at the University of Munich.

Georg Simon Ohm
Ohm's Law - Current-Circuits-Resistance-Calculation

Ohm's law defines the relationship between Voltage, Current, and Resistance. Where I is the current, measured in Amperes (Amps/A). R is the resistance, measured in Ohms (Ω). E is the electrical potential (voltage). And W is power, measured in Watts.


Common Ohms Laws are:

Watts equals Volts times Amps, or W = E x I. 

Another would be Amps = Watts divided by Volts or I = W / E. 


AMPS MEASURE CURRENT: The volume of the current (the number of electrons flowing past a given point per second) is measured in amperes or Amps.

VOLTS MEASURE PRESSURE: The pressure under which electricity moves is measured in volts. Electricity arrives at household circuits at a “pressure” of 120 or 240 volts.

WATTS MEASURE POWER: Power is measured in watts, and you can compute wattage by multiplying amperage and volts. 



Assume that a standard incandescent light bulb is drawing 1/2 amp from a 120-volt circuit that uses 60 watts of power (120 volts x 0.5 amps = 60 watts). To calculate amps, divide watts by volts. 

Assume an electric clothes dryer is using 240 volts and is rated at 7,200 watts pulling 30 amps (7,200 / 240 = 30). This means that the dryer must be protected by a 30-amp circuit breaker, and the wire carrying the current to it must be No. 10 copper, which is rated for 30 amps.

How much does it cost to operate my portable electric heater? An electric heater wattage is usually given on the unit itself. Assume it is 1,000 watts. Assume that the heater is used an average of 45 hours during winter months (half-hour per day for the three winter months), and the utility's electric rate during the winter is $0.068. Then, 1,000 watts/1,000 = 1 kW x 45 hours of operation = 45 kWh x $0.068 = $3.06.
Now, let's assume that we have an 8-amp heater. The calculation changes just a bit to 8 amps x 120 volts of household current = 960 watts/1,000 = 0.96 kW x 45 hours = 43.2 kWh x $0.068 = $2.94.

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Electrical current is actually the movement of electrons flowing along a conductor in much the same way as water flows through a pipe. The same fundamental principles apply in the same way: the bigger the pipe, the more flow it can handle. Conversely, smaller pipes can handle small supplies. This is the principle behind resistance.
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