Ohm's Law

As we know, the current that flows through a circuit is directly proportional to the voltage that creates it, usually from the battery's EMF. This proportionality can be represented as:

We also know that current is inversely proportional to resistance because the more resistive an object is, the less current that flows through that object. This proportionality can be represented as:

We have two very clear proportionalities so we can combine them to create Ohm's Law, which states the current flowing through a conductor between two points in a circuit is directly proportional to the voltage between those same two points, where the resistance is a constant of proportionality.

If we re-arrange the terms of this equation, we can see that the resistance of an object can be defined as the ratio between the voltage between two points on both sides of the object and the current between those same two points.

If we re-arrange the terms of this equation, we can see that the resistance of an object can be defined as the ratio between the voltage between two points on both sides of the object and the current between those same two points.

Electric power is just like mechanical power. It is the rate at which electrical work is done, usually on a resistor or electronic device with a nonzero resistance, per unit time, measured in Joules/second, or Watts(W). In real life, electric generators produce electric power but in simpler circuits, it's the battery that provides electric power.