5.2 The Ohm's Law Formula

This is the second week of Module 5 in the Navy Basic Electricity and Electronics series. This module is on the relationships between current, voltage, and resistance. The first section was:

5.1 Voltage, Resistance, and Current

1. You can calculate the current in a system without shutting it down and measuring it. You can use "Ohm's Law" if you know the voltage and the resistance. The formula is:

E=IR

The voltage equals the current times the resistance. We can rearrange the formula as well. Current equals the voltage divided by the resistance, and the resistance equals the voltage divided by the current.

2. You can use this formula for an entire circuit. You can also use it for a distinct part of a circuit.

3. There can be more complex situations where the value of one resistor is known but not the value of another. In such cases, knowing algebra will come in handy so that you can set up an equation and then solve for the unknown.

5.1 Voltage, Resistance, and Current

Module 5 of the Navy Basic Electricity and Electronics series starts today. This module is called Relationships of Current, Voltage, and Resistance. The first four modules were:

1. Electrical Current
2. Voltage
3. Resistance
4. Measuring Current and Voltage in Series Circuits

The first section of the new module is titled: "Voltage, Resistance, and Current." "The relationship of voltage, resistance, and current is probably the most important concept you will learn in your study of electricity" (6).

• You cannot really address current directly. You can only change it by increasing the force moving it (relates to voltage) or the resistance opposing it.
• When voltage goes up, current goes up. When voltage goes down, current goes down (assuming that resistance is held constant).
• So the amount of current is "directly proportional" to the amount of voltage.
• When resistance goes up, current goes down. When resistance goes down, current goes up (assuming voltage is constant). 
• EMF (electromotive force, which relates to voltage) and resistance are inherent quantities that depend on the physical components you are using in a circuit. Current is a secondary characteristic--it changes on the basis of the physical components.
• The relationships between voltage, resistance, and current were unfolded by George Simon Ohm (1789-1854). Ohm's Law states, "Current is directly proportional to voltage and inversely proportional to resistance."