Ohm’s Law: How to Apply it in Practice on a Vehicle

In 1827, a German mathematics professor, Georg Ohm, published a book that included his explanation of the behavior of electricity. His thoughts have become the basis for the understanding of electricity. He found it takes 1 volt of electrical pressure to push 1 ampere of electrical current through 1 ohm of resistance. This statement is the basic law of electricity and is known as Ohm’s law.
A simple electrical circuit is a load connected to a voltage source by conductors. The resistor could be a fog light, the voltage source could be a battery, and the conductor could be a copper wire.

A simple circuit consists of a voltage source, conductors, and a resistance or load.

In any electrical circuit, current (I), resistance (R), and voltage (E) are mathematically related. This relationship is expressed in a mathematical statement of Ohm’s law. Ohm’s law can be applied to
the entire circuit or to any part of a circuit. When any two factors are known, the third factor can be found. Using the circle shown in figure below, you can find the formula for calculating the unknown value. By covering the value you need to find, the necessary formula is shown in the circle.

Ohm's Law

• To find voltage, cover the E. The voltage (E) in a circuit is equal to the current (I) in amperes multiplied by the resistance (R) in ohms.
• To find current, cover the I. The current in a circuit equals the voltage divided by the resistance.
• To find resistance, cover the R. The resistance equals the voltage divided by the current.

It is very important to understand Ohm’s law. This includes understanding the relationships between volts, amps, and resistance. For example, when working with resistances in a series circuit, Ohm’s law allows for adding the resistances together to determine total circuit resistance. Resistances can be added together because they are like terms. This means that voltages also can be added together, just as amperages can be added together. Because volts and amps are not like terms they cannot be added together. Understanding these aspects of Ohm’s law will help you understand how to apply it not just to electrical circuits on paper but also in practice on a vehicle. It also explains how an increase or decrease in voltage, resistance, or current affects a circuit. For example, if the fog light in Figure 15–18 has a 6 -ohm resistance, determine the current in the circuit. Since cars have a 12 -volt battery, you know two of the values in the fog light circuit and calculating the third value is quite simple:

In a clean, well-wired circuit, the fog lights will draw 2 amperes of current. What would happen if resistance in the circuit increases due to corroded or damaged wires or connections? If bad connections add 2 ohms of resistance to the circuit, the total resistance is 8 ohms. Therefore, the amount of current through the circuit decreases.

Same circuit as shown in Figure 15–18 but this one has a corroded wire, represented by the additional resistor.

If the lights are designed to operate at 2 amperes, this decrease to 1.5 amperes causes them to burn dimly. Removing the corrosion or installing new wires and connectors will eliminate the unwanted resistance. Now the correct amount of current will flow through the circuit, allowing the lamp to burn as brightly as it should.