Electrical Engineering: Basic Concepts

• Electrical Engineering is introduced

Basic Concepts

• The basic concepts include electricity, charge, current, voltage, and power and energy.

Electricity

• Electricity results from the existence and interactions of electric charge.

Charge

• Charge can be observed/experienced/used in numerous scenarios.
• It is a characteristic property of subatomic particles, responsible for electric phenomena.
• Electrons are negatively charged (-1.602×10-19 C), and protons are positively charged (1.602×10-19 C).
• The unit of electric charge is the coulomb (C), where 1 C = 6.25 × 10^18 elementary charges where e equals the elementary charge or charge of proton.
• "Charged" particles exhibit forces; like charges repel, and opposite charges attract.
• Charge is a fundamental force in nature.

Coulomb's Law

• The electrostatic force F1,2 exerted on charge 1 due to charge 2 is given by F1,2 = ke (q1q2/r^2), where F1,2 is measured in Newtons.
• ke is the Coulomb constant, approximately 8.987 x 10^9 Nm^2C^-2.

Electric Current

• Electric current is charge in motion, or the flow of charge, measured in Amperes.
• This movement of charge can result from moving electrons in a conductive material or moving ions in charged solutions.
• An ampere (A) is the number of electrons having a total charge of 1 C moving through a given cross section in 1 second.
• Current is defined as flowing in the direction of positive charge flow.
• The formula for electric current is I = Q/t, where I is current in amperes, Q is charge in coulombs, and t is time in seconds.

Electrical Circuits

• Electrical circuits are an interconnection of electrical elements linked in a closed path, enabling continuous current flow.
• Circuit diagrams are the standard for electrical engineers.

Direct Current (DC)

• Direct current (DC) has a constant magnitude.

Alternating Current (AC)

• Alternating current (AC) varies in magnitude and direction.

Voltage

• Voltage is the driving "force" of electrical current between two points.
• The formula is V = W/Q, where V is voltage in volts which is equivalent to joules per coulombs, W is energy in joules, and Q is charge in coulombs.
• The voltage across an element is the work (energy) needed to move a unit of positive charge from the "–" terminal to the "+" terminal.
• A volt represents the potential difference when 1 joule of energy moves 1 coulomb of charge between two points.

Power

• Power (P) is the rate at which energy is converted or work is performed, given by P = W/t = IV, where P is in watts, W is in joules, and t is in seconds.
• A watt is equivalent to using or converting 1 joule of energy in 1 second.

Resistors

• Resistance (R) impedes the flow of current, measured in Ohms (Ω)
• Resistivity (ρ) refers to a material's ability to resist current flow, measured in Ohm-meters (Ω-m).

Ohm's Law

• A version of the the formula is V=IR, where V is the voltage, I is the current, and R is the resistance.

Capacitors

• Capacitors consist of a pair of conductors separated by a dielectric or insulator.
• Electric charge is stored in the plates, and a capacitor can become "charged".
• When voltage exists across the conductors, it provides the energy to move charge from the positive plate to the other plate.
• Capacitance (C) measures a material's ability to store charge in the form of separated charge or an electric field.
• Capacitance is the ratio of charge stored to voltage difference between two plates.
• Capacitance is measured in Farads (F).
• The formula for capacitance is C = Q/V, where C is capacitance in farads, Q is charge in coulombs and V is volatage.
• The capacitor plate attached to the negative terminal accepts electrons from the battery.
• The capacitor plate attached to the positive terminal accepts protons from the battery.
• Work must be done by an external influence (battery) to separate charge between the plates in a capacitor.
• Charge is stored in the capacitor until the external influence is removed, and the separated charge is given a path to travel and dissipate.
• The formula for the work exerted to charge a capacitor is W = (1/2)CV^2.

Inductors

• An inductor, a two-terminal element with N turns, stores energy in a magnetic field.
• Inductance (L) quantifies a device's ability to store energy in a magnetic field, measured in Henries (H).
• The magnetic field from an inductor can generate an induced voltage, expressed as v = L(di/dt) which can drive current.
• While building the magnetic field, the inductor resists current flow.
• Inductors can store energy in a magnetic field when current passes through them.
• The work required to establish current through the coil is W = (1/2)LI^2

Transformers and Alternators

• Inductors are used in both transformers and alternators, allowing voltage conversion and current generation
• If the current through an ideal voltage source is completely determined by the external circuit, it is considered an independent voltage source.

Ideal Voltage Source

• An ideal voltage is a circuit element where the voltage across the source is independent of current.
• The internal resistance of an ideal voltage source is zero.

Ideal Current Source

• An ideal current source is a circuit element where the current through the source is independent of the voltage across it.
• The internal resistance of an ideal current source is infinite.
• If the voltage across an ideal current source is completely determined by the external circuit, it is considered an independent current source

Dependent Sources

• Dependent or controlled sources depend on a different voltage or current in the circuit.

Series Circuits

• A series circuit has only one current path.
• Current through each component is the same.
• In a series circuit, all elements must function for the circuit to be complete.

Parallel Circuits

• A parallel circuit has more than one current path branching from the energy source.
• Voltage across each pathway is the same.
• In a parallel circuit, separate current paths function independently of one another.

Parallel Voltage Sources

• For parallel voltage sources, the voltage is the same across all batteries, but the current supplied by each element is a fraction of the total current.