Roadwolf's portal for his random thoughts and ponderings

Roadwolf's Electronics Series: Part 3, Ohm's Law


Electrical current is when an electrical charge travels through a conductor from an area of high potential, to an area of low potential. The electrons flow from a negatively charged area, to an area of positive charge.

A current flowing through a conductor creates a magnetic field around the conductor. A good way to see this for yourself is to align a wire along the East-West poles of a magnetic compass. Align the compass so that North is pointing north as it should be, then apply a current through the wire, by attaching each end of the wire to each end of a D Cell battery. You should notice the compass needle move. Do not allow the wire or battery to heat up too much!

There are two main types of current which we need to be familiar with. The first being Direct Current. The second being Alternating Current. But firstly, we need to familiarize ourselves with the 4 different ways to measure electricity, and Ohm's Law. Ohm's Law is an important bit of information to learn for any foundation in understanding electronics.

Current (I): Current is measured as an Ampere. One Ampere is 6,241,509,300,000,000,000 (6.2415093×1018) electrons passing through a single point in a conductor in the time span of one second. This is the amount of electricity which is flowing through a specific point in a circuit.

Voltage (V): Voltage is best described as the difference in electrical charge between the positive and negative side of a circuit. It is also called Potential. Voltage Drop is the difference in voltage between 2 parts of a circuit. Often this would be measured by referencing one probe to the 'common' or 'ground' of a circuit.

Power (P): Power is the measurement of how much work is actually being preformed by the electrical circuit. This is measured in Watts. This can also be compared with Horsepower (1W = 0.0013 HP) and BTU's (1W = 3.414 BTU/h).

Resistance (R): Resistance, sometimes referred to as Impedance, is the measurement of how much a conductor resists electrons. Conductors are not perfect, and most will have some natural loss. This loss is called Resistance. Resistance slows down the flow of electrons in the circuit, limiting an otherwise stronger flow, to a more manageable trickle.

The water analogy sums it up nicely. The water level, or back pressure, is comparable to Voltage. The tap is comparable to Resistance. The stream of water is comparable to Current, and the Turbine is comparable to Power.

Ohm's Law:

The above four properties are all fundamental in diagnosing and designing electrical circuits. With only two of the above values, you can figure out any other value. This is ohm's law.

V = I x R

I = V / R

R = V / I

P = V x I


P = (I x I) R

A voltage of One Volt, will force a current of One Amp, through a resistance of One Ohm, which will create One Watt of power!

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