Electrical Quantities II. Relationships between quantities
The online simulations of electrical quantity relationships on this page let you explore how the main electrical quantities in a circuit—voltage, current, and resistance—are related. Through different configurations, you’ll observe how current changes when voltage or resistance is modified and begin to recognize patterns that will help you better understand how electric circuits behave.
This Thematic Unit is part of our Circuits collection
STEM OnLine mini dictionary
Current Intensity
Amount of electric charge passing through a cross-section of the conductor per unit of time, measured in Amperes (A).
Electric Power
Rate at which energy is consumed or supplied in a circuit, calculated as P = V · I and measured in Watts (W).
Electrical Resistance
Measure of the opposition that a material presents to the flow of electrical current. The SI unit of measurement is the Ohm (Ω).
Ohm’s Law
Fundamental principle stating that current intensity is directly proportional to voltage and inversely proportional to resistance: V = I · R.
Voltage (Tension)
Electric potential difference between two points in a circuit that drives the movement of charges, measured in Volts (V).
What does it mean for electrical quantities to be related
In an electric circuit, it’s not enough to understand each quantity in isolation. Voltage, current, and resistance don’t act independently, they’re interconnected. This means that changing one can affect the others. For example, if you increase the voltage of a power source, the current may also change. And if you adjust the resistance, the current might be affected as well.
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.
STEM OnLine mini dictionary
Current Intensity
Amount of electric charge passing through a cross-section of the conductor per unit of time, measured in Amperes (A).
Electric Power
Rate at which energy is consumed or supplied in a circuit, calculated as P = V · I and measured in Watts (W).
Electrical Resistance
Measure of the opposition that a material presents to the flow of electrical current. The SI unit of measurement is the Ohm (Ω).
Ohm’s Law
Fundamental principle stating that current intensity is directly proportional to voltage and inversely proportional to resistance: V = I · R.
Voltage (Tension)
Electric potential difference between two points in a circuit that drives the movement of charges, measured in Volts (V).
Explore the exciting STEM world with our free, online, simulations and accompanying companion courses! With them you’ll be able to experience and learn hands-on. Take this opportunity to immerse yourself in virtual experiences while advancing your education – awaken your scientific curiosity and discover all that the STEM world has to offer!
Simulations of relationships between electrical quantities
Current and resistance
What happens to the current when you change the resistance? This circuit is the same as in the previous simulation, but this time you’ll try different resistance values while keeping the voltage constant. Watch how the current responds as the opposition to flow increases or decreases.
General pattern. Ohm’s Law
In this simulation, you’ll build a circuit with a battery, a resistor, a light bulb, and a fuse. You can change the voltage and resistance values and observe how the current changes. Pay attention to the bulb’s brightness, the fuse’s state, and the current readings. What happens when you increase the voltage? What if you change the resistance? Can you find different combinations that produce the same current? Experiment with the controls and see how the three electrical quantities are related. You’ll find that the same rule always applies: Ohm’s Law.
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“If I have seen further, it is by standing on the shoulders of giants”
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Become a giant
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Test your knowledge
Why are electrical quantities said to be related to one another in a circuit?
How are the relationships between voltage, current and resistance interpreted when analyzing a circuit?
Why does changing voltage or resistance make the current change too?
What happens if you increase voltage but do not change resistance?
What happens if you increase resistance while voltage stays the same?
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