What is Ohm’s Law?
Understanding voltage, current & resistance
The relation between voltage, current, and resistance forms the basis of Ohm’s law, which is translated in the formula below where V is voltage, I is current, and R is resistance:
V = I · R
In short, voltage is cause and current is effect. When a voltage source is connected to a closed loop circuit, the voltage will produce a current that flows around the circuit. Voltage is the force, current is the flow, and resistance is restriction against the current.
Increasing voltage increases current flow (proportionate)
Voltage measures the difference in charge between 2 points in a circuit that have different electrical potential (positive/negative). It is the electromotive force that drives electric current by moving electrons through a circuit. Greater voltage means greater ability to push the electrons through the circuit to move the electrical current from one point to another.
Unit of measure: volt V
Current is the rate at which charge is flowing. It is the continuous movement of electrons through the conductor within a circuit that is forced into motion by the voltage source. Current is measured in amps/amperes, which is the number of electrons or charge passing a certain point in the circuit in one second. Current can flow in a single direction (direct current) or alternate back and forth (alternating current) and may be positive or negative depending on the direction of the flow around the circuit.
Unit of measure: ampere, “amp” A
Resistance is a material’s (ex: conductor and insulator) tendency to resist the flow of charge. It is the opposition to current flow in a circuit. Resistance is quantity relative between 2 points and can only be positive in value.
Unit of measure: ohm Ω
Increasing resistance decreases current flow (inversely proportionate)
How It Works Together
Voltage, current, and resistance are all part of an electrical circuit. Within a closed circuit, one point has more charge than the other causing loose electrons to move and drift back to the protons due to their attraction. This creates a flow of electrons known as electrical current.
Voltage can exist in a circuit without current but current cannot exist without voltage. Resistance correlates with the inverse of current. Whereas higher voltage corresponds to higher current flow, higher resistance corresponds to lower current flow. The amount of current in a circuit depends on the amount of voltage available and the amount of resistance in the circuit to oppose electron flow.