Faraday’s Law, Capacitance, and Capacitors for Beginners
Concept
Laws
Capacitors and magnetic induction are two key building blocks of electronics. Whether you're working with circuits, motors, or sensors, understanding how capacitance and Faraday's Law work can help you design and troubleshoot with confidence. This article breaks these concepts down for beginners, step by step.
What is Capacitance?
Capacitance is a fundamental property of every electrical circuit. Technically, capacitance refers to a component or system's ability to store electric charge when a voltage is applied to it, usually in capacitors.
Even when you don't intentionally add a capacitor to a circuit, small amounts of capacitance can still appear. This is called stray capacitance, and it happens when two conductors, like copper wires, are close together and separated by an insulator (like air or plastic). These small electric fields can unintentionally store and transfer energy. This usually is not a problem in low-speed circuits, but in high-speed applications, the signals could decay, and your circuit may fail. It's important to use shorter wires whenever possible to limit the stray capacitance.
Capacitance is measured in farads (F). Typically, 1 farad is quite large for typical capacitor applications. Some more common measurements are microfarads (μF), nanofarads (nF), or picofarads (pF). The formula for calculating capacitance is below:
C = Q/V
Where
- C is capacitance in farads
- Q is the charge stored in coulombs
- V is the voltage in volts
What are Coulombs?
A coulomb measures how much electric charge flows. One ampere of current means one coulomb of charge is flowing per second. Essentially, a coulomb is a measurement of how many electric charges (electrons or protons) are moving. One coulomb equals approximately 6.24 • 1018 electrons. Unlike energy (measured in joules), coulombs measure how much charge flows through a circuit. For example, if a 47μF capacitor is charged with 5V,
.000047 • 5 = .000235 C
The capacitor used .000235 coulombs. This equation was derived from the C = Q/V to get CV = Q.
What Is Faraday's Law of Induction?
Faraday's law of induction states that a changing magnetic field creates an electromotive force, or voltage, in a circuit. This may seem daunting, but you have most likely seen this law at work in real life. For example, let's take a look at an induction motor, also called a generator.
When I spin the motor, it generates electricity by a changing magnetic field near a copper wire (or the circuit). Using this law, you can also generate electricity by passing a magnet through a pipe that has copper wire wound into a coil on the outside of the pipe.
How does Faraday's Law of Induction Work?
Electrical current, at a subatomic level, is electrons being “pushed” around inside a conductor. When a magnetic field is moved close to a conductor, the field pulls the electrons with the magnet, and this generates current. This law is important to our everyday lives, as most of the power in the world is generated using techniques involving this law.
What are Capacitors Used For in Real Life?
Capacitors can be charged and discharged quickly, making them useful for balancing power flow, filtering signals, and timing operations (such as with the 555 timer) in electronic circuits.
However, if you want to have the capacitor slowly charge and discharge, you can attach a resistor to one of the capacitor's terminals. Some more interesting things capacitors are used for:
- Camera flashes
- Tasers
- AC to DC conversion
- Temporary energy storage
Capacitors have many uses and are one of the fundamental electrical components. Check out our article about using capacitors in real life for more information on how to use these components yourself.
Conclusion
Faraday's laws and their applications led to important concepts that significantly impact the day-to-day lives of many people. These laws led to the development of methods to generate electricity and the creation of a fundamental electrical component. If learning about capacitors and the laws behind them interests you, check out our article about Ohm's Law and resistance. If you want to learn more about how electrical components work, check out our article about getting started with circuits. Understanding these principles is essential for anyone learning electronics, as they form the basis for analyzing circuits, designing components, and troubleshooting real-world electrical systems.
