Electricity

Inductor

A coil of wire that stores energy in a magnetic field.

Energy in an Inductor

Calculated using the formula E = half L I squared.

Self Inductance

When a change in flux induces a back EMF in the coil itself.

Back EMF Formula

E equals negative L times change in current over time.

E = -L (I/t)

Mutual Inductance

The wireless transfer of energy by inducing electricity in a nearby coil.

Magnetic Flux

The number of magnetic field lines passing through a given area.

Magnetic Flux Formula

Phi (magnetic flux) = magnetic field strength (B) x area (A).

Lenz's Law

Nature abhors a change in flux, inducing a current to oppose it.

Faraday's Law

A changing magnetic flux generates a voltage or EMF.

Capacitor

Two metal plates separated by a dielectric that store an electric field.

Capacitance Formula

C equals charge divided by voltage (Q over V).

Dielectric

An insulating material between capacitor plates that increases capacitance.

Time Constant for Inductor

Time constant (Tau) = inductance divided by resistance (L over R).

Time Constant for Capacitor

Time Constant (Tau) equals resistance times capacitance (RC).

Kirchhoff's Current Law

The total current entering a junction equals the total current leaving.

Kirchhoff's Voltage Law

The sum of all voltages around any closed loop is zero.

Internal Resistance

Imperfections in a battery that transform electrical energy into heat.

EMF (Electromotive Force)

Total voltage when current does not flow YET

Terminal Voltage

Total Voltage DURING current flows

V/Irms is Root - Mean - Square voltage / current

A way of determining the avergae voltage / current in an AC circuit

Reactance

A form of resistance in inductors and capacitors, measured in Ohms as well with symbol X

Resistance Vs Reactance

Resistance is constant - Resistor

Reactance depends on frequency of AC voltage - Capacitor and Inductors

AC Circuit

Alternating Current Circuit - an electrical path where the current is flowing back and forth instead of moving in just one steady direction

DC Circuit

Direct Current Circuit - a closed loop where electricity flows in only one direction

RC Circuit

Resistor - Capacitor Circuit - a basic electrical setup that combines a resistor (which slows down or limits the flow of electricity) and a capacitor(which stores and releases electrical energy, much like a tiny rechargeable battery)

RL Circuits

Resistor - Inductor Circuit - an electrical circuit that combines a resistor (R) and an inductor (L) connected in series or parallel and driven by a voltage or current source

Impedance

Symbol Z, measured in Ohms. The total resistance AND reactance in a circuit

Transformers

a passive electrical device that transfers electrical energy from one circuit to another using electromagnetic induction, usually to change alternating current (AC) voltage levels without altering its frequency

Phasing

the time or position relationship between alternating current (AC) waves

Phase between voltage and current - In Phase

In-Phase: When voltage and current reach their zero points and peaks at the exact same time (typical in simple resistive loads like a heater or incandescent bulb), they are in phase (0° difference)

Phase between voltage and current - Out Of Phase

Out-of-Phase (Leading or Lagging): When a circuit includes inductive components (like motors or transformers) or capacitive components, the current falls out of sync with the voltage.

• In an inductive circuit, the current lags behind the voltage (often by up to 90°).

• In a capacitive circuit, the current leads the voltage.

• When voltage and current are out of phase, part of the energy sloshes back and forth instead of doing useful work, creating what is known as reactive power (measured in VARs)

Resonance

when the pushing frequency of an electrical source matches the natural rhythm of a circuit, causing energy to flow back and forth easily and build up to maximum strength

Resonant Frequency Formula

𝑓=1/(2𝜋√𝐿𝐶)

Inductance

tendency to oppose sudden changes in electric current

opposes by storing inductance energy and uses this.

Capacitance

an object's or circuit's ability to store and hold an electrical charge

Magnetic Permeability

measures how easily a material allows magnetic field lines to pass through it

What happens when magnetic field lines are concentrated in a high magnetic permeability material

stores more inductance energy therefore stronger back EMF and increases flux linkage

Flux linkage

the total magnetic flux that interacts with or passes through a multi-turn coil or winding

calculating time constant for CHARGING

1t = x 0.63

2t = x 0.86

3t = x 0.95

4t = x 0.98

calculating time constant for DISCHARGING

1t = x 0.37

2t = x 0.14

3t = x 0.5

4t = x 0.2

5t = x 0