Basics of Voltage, Current, and Resistance

Created on: 2025-02-14

Understanding voltage, current, and resistance is fundamental to learning electronics. These three properties form the foundation of how electrical circuits work. Whether you're a beginner or looking to refresh your knowledge, this guide will help you grasp these essential concepts in a clear and practical way.

What is Voltage?

Voltage, also called electrical potential difference, is the force that pushes electrons through a conductor, like a wire. It is measured in volts (V) and is often provided by a power source such as a battery or a power supply.

Analogy: Water Pressure

To understand voltage, think of an electrical circuit as a water system:

Voltage is like water pressure in a pipe—it determines how strongly the water (electricity) is pushed through.
Higher voltage means a greater force moving electrons through a circuit.

Common Sources of Voltage

A AA battery* provides 1.5V
A 9V battery provides 9 volts
A typical household power outlet supplies 120V or 230V AC

* Technically an AA "battery" is actually a cell. Batteries consist of two or more cells.

A 9V battery — An Example of a 9V Battery used in Electronics

What is Current?

Current is the flow of electric charge through a conductor. It is measured in amperes (A) and represents how many electrons are moving through a circuit per second.

Circuit diagram showing current flow in a circuit — A Circuit Diagram Showing Current Flow

Analogy: Water Flow

Continuing with the water pipe analogy:

Current is like the amount of water flowing through the pipe.
More current means more electrons flowing through a circuit.

Types of Current

Direct Current (DC): Flows in one direction (e.g., batteries, USB power).
Alternating Current (AC): Changes direction periodically (e.g., household electricity).

What is Resistance?

Resistance is the opposition to the flow of electric current. It is measured in ohms (Ω) and determines how much a material resists the movement of electrons.

A bundle of resistors joined with tape — Quarter Watt Resistors used in Hobby Electronics Circuits

Analogy: Narrow vs. Wide Pipes

Resistance is like a narrow section in a water pipe—it slows down the flow of water (electricity).
The higher the resistance, the harder it is for current to flow.

Factors Affecting Resistance

Material: Conductors like copper have low resistance, while insulators like rubber have high resistance.
Length of wire: Longer wires have more resistance.
Thickness of wire: Thicker wires have less resistance.
Temperature: Higher temperatures increase resistance in most materials.

Ohm's Law: The Relationship Between Voltage, Current, and Resistance

The relationship between voltage, current, and resistance is defined by Ohm's Law:

V = I × R

Where:

V = Voltage (volts)
I = Current (amperes)
R = Resistance (ohms)

How Ohm's Law Works

If you increase the voltage, the current will increase (if resistance stays the same).
If you increase the resistance, the current will decrease (if voltage stays the same).

Example Calculation

If a circuit has a 9V battery and a resistor of 3Ω, we can calculate the current:

I = V / R = 9V / 3Ω = 3A

This means a current of 3 amperes flows through the circuit.

Practical Applications

Understanding these three properties is essential for designing and troubleshooting electronic circuits. Here are some examples:

Choosing the right resistor: When working with LEDs, you need to limit current using a resistor to prevent burning out the LED.
Measuring voltage and current: Using a multimeter, you can test batteries, check circuits, and diagnose electrical issues.
Building circuits safely: Knowing how voltage and current interact helps prevent overheating components and short circuits.

Key Takeaways

Voltage (V): Pushes electrons through a circuit (like water pressure).
Current (A): The flow of electrons (like water flow).
Resistance (Ω): Opposes the flow of current (like pipe width affecting water flow).
Ohm's Law: Defines the relationship between voltage, current, and resistance.

Understanding these basics will set you on the path to mastering electronics. Whether you're experimenting with circuits, building projects, or troubleshooting devices, voltage, current, and resistance will always be at the core of your work!

Next Steps

If you're eager to dive deeper into electronics, check out our other beginner-friendly articles on circuit components, breadboarding, and basic soldering techniques!