Module 3 Electrical Fundamentals flashcards

37 cards. Read the term and the definition here. The deck at the top of this page is optional.

Elementary charge

The smallest free charge, 1.602×10⁻¹⁹ coulomb, carried by one electron (negative) or one proton (positive). One coulomb holds about 6.24×10¹⁸ electrons.

Valence electrons

Electrons in the outermost shell of an atom. They determine chemical bonding and electrical behaviour: few valence electrons mean a conductor, many mean an insulator.

Ionization

The process of removing one or more electrons from an atom, leaving a positive ion. Free electrons and ions produced this way allow current to flow through gases.

Coulomb's law

The force between two point charges is proportional to the product of the charges and inversely proportional to the square of their separation: F = k·q₁·q₂/r².

Triboelectric charging

Charging by friction, in which contact between dissimilar materials transfers electrons from one to the other, leaving one body positive and the other equally negative.

Charging by induction

Bringing a charged body near an isolated conductor without contact, causing charge separation; earthing one side then leaves the conductor with a net charge opposite to the inducing body.

Bonding and earthing

Bonding connects two conductors so they sit at the same potential. Earthing connects equipment to ground, safely draining static charge and limiting shock risk.

Conductor versus insulator

A conductor (copper, aluminium, carbon) has many free electrons and low resistance. An insulator (glass, rubber, dry air) has tightly bound electrons and very high resistance.

Electric current

The rate of flow of electric charge, measured in amperes. One ampere equals one coulomb of charge passing a point per second: I = Q/t.

Potential difference

The energy transferred per unit charge between two points, measured in volts. One volt equals one joule per coulomb: V = W/Q.

Electromotive force

The open-circuit potential a source can supply, in volts. Terminal voltage falls below EMF by the internal drop I·r when current flows.

Faraday's law

The EMF induced in a coil equals the negative rate of change of magnetic flux linkage: E = −N·dΦ/dt. Faster flux change or more turns gives more EMF.

Lenz's law

An induced current always flows in the direction that opposes the change in flux producing it. This explains the negative sign in Faraday's law.

Piezoelectric generation

Generation of an EMF by applying mechanical pressure to certain crystals such as quartz. Used in spark igniters, pressure sensors, and some microphones.

Primary versus secondary cell

A primary cell (alkaline, carbon-zinc) is not rechargeable because its electrode reaction is irreversible. A secondary cell (lead-acid, lithium-ion) can be recharged.

Cells in series and parallel

Series connection adds EMFs but keeps one cell's current capacity. Parallel connection keeps one cell's EMF but adds capacities in ampere-hours.

Internal resistance

The resistance inside a source that causes terminal voltage to fall as current rises: V = E − I·r. It increases as a battery discharges or ages.

Ampere-hour capacity

The charge a battery can deliver, equal to discharge current in amperes multiplied by time in hours. A 50 Ah battery gives 5 A for about 10 hours.

Series circuit rules

In a series circuit the current is the same through every component, voltages add, and total resistance is the simple sum R₁ + R₂ + R₃.

Parallel circuit rules

In a parallel circuit the voltage is the same across every branch, branch currents add, and total resistance is less than the smallest branch resistance.

Kirchhoff's voltage law

Around any closed loop, the algebraic sum of EMFs equals the sum of voltage drops; equivalently the total sum is zero. Basis of loop analysis.

Voltage divider

Two series resistors split the supply in proportion to resistance: V_out = V_in × R₂/(R₁ + R₂), taken across R₂.

Resistivity formula

Resistance of a conductor is R = ρ·l/A: proportional to resistivity and length, inversely proportional to cross-sectional area. Doubling length doubles resistance.

Resistor colour code

Bands give digits (black 0 to white 9), then a multiplier. Gold means ±5%, silver ±10%, brown ±1%, red ±2%, and no tolerance band means ±20%.

Temperature coefficient

The fractional change in resistance per degree Celsius: R = R₀[1 + α(T − T₀)]. Metals have positive α; carbon and semiconductors have negative α.

Electrical power formulas

Power in watts equals V·I, I²R, or V²/R. Energy is power multiplied by time, with one kilowatt-hour equal to 3.6 megajoules.

Maximum power transfer

A source delivers maximum power to a load when load resistance equals source internal resistance. Efficiency at that point is only 50 percent.

Capacitance formula

Capacitance is charge per volt, C = Q/V, measured in farads. A one-farad capacitor stores one coulomb at one volt.

Capacitor time constant

The product R·C in seconds. After one time constant a capacitor charges to 63.2 percent of supply voltage and discharges to 36.8 percent of its starting voltage.

Capacitive reactance

Opposition a capacitor offers to AC: X_C = 1/(2πfC) ohms. It falls as frequency or capacitance increases, and is infinite at zero frequency (DC).

Magnetic flux density

Flux density B equals flux per unit area, B = Φ/A, measured in teslas. One tesla equals one weber per square metre.

Inductive reactance

Opposition an inductor offers to AC: X_L = 2πfL ohms. It rises with frequency and inductance, and is zero at DC once current is steady.

Inductor energy storage

An inductor stores energy in its magnetic field: W = ½·L·I². Current cannot change instantaneously, so the field collapses through a path such as a flyback diode.

RMS and peak values

For a sine wave, RMS equals peak divided by √2, about 0.707 of peak. RMS is the value that produces the same heating as an equal DC value.

Impedance and phase angle

Impedance Z = √(R² + (X_L − X_C)²) ohms. Phase angle φ = arctan[(X_L − X_C)/R]; current lags when inductive, leads when capacitive.

Series resonance

Occurs when X_L equals X_C, at f = 1/(2π√(LC)). Impedance is then minimum and equal to R, so current is maximum and in phase with voltage.

Power factor

The ratio of true power to apparent power, cos φ, equal to R/Z. A low value means large reactive current; parallel capacitors correct inductive loads.