Electrical Quantities II. Relationships between quantities

Relationships between pairs of quantities

To understand how a circuit behaves, you need to look at how quantities relate to one another—not just at each one separately. This section explores the relationship between pairs of quantities. You’ll see that when one is held constant and another is changed, the third responds in a predictable way. These partial relationships will help you uncover a more general pattern behind circuit behavior.

Voltage and current

When you increase the voltage in a circuit, the current also increases. This happens because voltage acts like a “push” that drives the current more strongly. If the resistance in the circuit stays the same, that extra push results in more electric charge moving per second—in other words, a higher current. Put simply: higher voltage means higher current, as long as resistance remains constant. This direct relationship is one of the clearest patterns you can observe when adjusting a power source.

Current and resistance

In a circuit with constant voltage, increasing the resistance causes the current to decrease. It’s as if resistance adds more obstacles to the flow of current: the higher the resistance, the harder it is for charge to move. This means that higher resistance leads to lower current, as long as the voltage doesn’t change. This inverse relationship is another key pattern you’ll notice when analyzing how electrical quantities behave.

Voltage and resistance

In some cases, you may want to keep the current constant in a circuit. To do that, it’s not enough to fix just one quantity—voltage and resistance must be adjusted together. If you increase the resistance, you’ll also need to increase the voltage to maintain the same current. This shows that, while voltage and resistance aren’t directly related like in the previous cases, they are connected when trying to control circuit behavior.

Voltage, current, and resistance: Ohm’s Law

In the previous section, we looked at relationships between pairs of quantities. But the most interesting part comes when we relate all three. This relationship isn’t arbitrary—it follows a consistent pattern that appears in all circuits and is known as Ohm’s Law.

Ohm’s Law tells us that current is directly proportional to voltage and inversely proportional to resistance. In formula form:

I = V / R

In the simulations in this unit, you’ll see this relationship in action and confirm how it holds true in different scenarios.