Ohm's Law: Notes
The key to intelligent troubleshooting of electrical circuits is a thorough understanding of Ohm's Law. Ohm's Law states that the current flowing in a circuit varies directly with the voltage and inversely with the resistance.
The pressure of one volt applied to one Ohm of resistance will cause one amp of current to flow. If the voltage increases, current will increase. If resistance increases, current will decrease.
Knowing any two of the three factors (volts, resistance or current) enables the third factor to be calculated using Ohm's Law.
The mathematical expression is:
Volts = Resistance X Current
This formula is expressed in the Ohm's Law Triangle.
To find a missing factor, insert the known
factors in the appropriate position and perform the math. A horizontal line between two factors means to divide, a vertical line means multiply.
Understanding of Ohm's Law is essential in the diagnosis of electrical problems. A practical understanding of how the three factors affect each other is equally useful.
- Source voltage is not affected by current or resistance. It can only have three states.
Too low - Current flow will be low.
Too high - Current flow will also be too high.
Correct voltage - Current flow will be dependent on the resistance.
- Current Flow will be directly affected by either voltage or resistance.
High voltage or low resistance will cause an increase in current flow.
Low voltage or high resistance will cause a decrease in current flow.
- Resistance is not affected by either voltage or current. Resistance like source voltage can have only three states.
Too low - current will be too high if the voltage is ok.
Too high - current flow will be low if the voltage is ok.
Correct resistance - current flow will be high or low, dependent on voltage.