Free EASA Module 3 Exam Flashcards

The subatomic particle carrying a single negative charge; it orbits the nucleus in shells, and its movement between atoms is what constitutes electric current.

Both reside in the atom's nucleus: the proton carries a positive charge (balancing the atom's electrons), while the neutron carries no charge at all and adds mass only.

The number of electrons in an atom's outer (valence) shell predicts its conductivity: 1-3 valence electrons = good conductor, 4 = semiconductor, 5-8 = insulator.

F = k x Q1 x Q2 / d-squared - the force between two charged bodies is directly proportional to the product of their charges and inversely proportional to the square of the distance between them.

EMF is the open-circuit voltage generated by the source itself; PD is the voltage measured across a component once current is flowing. PD is always less than EMF because some voltage is lost across the source's own internal resistance.

Conventional current is defined as flowing from the positive terminal to the negative terminal; the actual electrons physically move the opposite way, from negative to positive. Circuit diagrams and Fleming's rules use conventional flow.

Friction (triboelectric/static charge), pressure (piezoelectric effect), heat (thermocouple/Seebeck effect), light (photovoltaic cell), chemical action (battery), and magnetism (electromagnetic induction).

Rubbing two dissimilar materials together transfers electrons between them, leaving one surface positively charged and the other negatively charged - the basis of static electricity buildup, which is why aircraft are bonded/grounded during refuelling.

A primary cell's chemical reaction is not reversible, so it cannot be recharged and is discarded once flat. A secondary cell's reaction is reversible, so it can be recharged and reused many times.

Lead-acid uses dilute sulphuric acid, and its specific gravity (checked with a hydrometer) reliably indicates state of charge. NiCd uses potassium hydroxide, and - unlike lead-acid - its specific gravity stays essentially constant regardless of charge state, so it cannot be used to judge charge.

Connecting cells in series adds their EMFs together (same current capacity as one cell); connecting cells in parallel adds their current capacity together (same EMF as one cell). Either way, terminal voltage = EMF minus (current x internal resistance), so it sags under load.

V = I x R. Rearranged: I = V/R to find current, or R = V/I to find resistance - the three forms needed for every DC circuit calculation.

The sum of currents flowing into a junction equals the sum of currents flowing out of it - current is conserved at every node, with zero net current accumulating there.

Around any closed loop, the sum of the EMFs equals the sum of the voltage drops - energy supplied by sources in a loop is fully accounted for by the drops across its components.

Current is the same at every point (only one path exists); total resistance is the simple sum of all resistors; supply voltage divides across components in proportion to their resistance (voltage divider: V2 = V x R2/Rtotal).

Voltage is the same across every branch; current divides between the branches; total resistance is always less than the smallest branch resistance (1/Rtotal = 1/R1 + 1/R2 + ...; for two resistors, use product over sum).

Each colour band represents a digit: Black 0, Brown 1, Red 2, Orange 3, Yellow 4, Green 5, Blue 6, Violet 7, Grey 8, White 9 - read the first bands as significant digits, then apply the multiplier band.

The final band states manufacturing tolerance: Gold = plus/minus 5%, Silver = plus/minus 10%, no band = plus/minus 20%. A tighter tolerance means the actual resistance is guaranteed closer to the printed value.

R = (rho x L) / A - a conductor's resistance rises with its length (L) and its material's resistivity (rho), and falls as its cross-sectional area (A) increases.

An NTC (negative temperature coefficient) thermistor's resistance falls as it heats up, useful for temperature sensing. A PTC (positive temperature coefficient) thermistor's resistance rises as it heats up, useful for overcurrent/overheat protection.

A four-arm resistance bridge is balanced (zero galvanometer deflection) when R1/R2 = R3/R4 - this ratio lets an unknown resistor be measured precisely against three known ones.

Power can be found three ways depending on what you know: P = V x I, P = I-squared x R, or P = V-squared / R. Energy consumed over time is W = P x t.

C = Q/V, measured in farads (F) - capacitance is the amount of charge (Q) a capacitor stores per volt (V) applied across its plates.

Capacitance increases with larger plate area and higher dielectric permittivity between the plates, and decreases as the plate separation (gap) increases.

This is the opposite of the resistor rule: capacitors in series combine like parallel resistors (total value drops, product-over-sum for two), while capacitors in parallel simply add together (total value rises).

Tau = R x C. After one time constant, a charging capacitor reaches about 63% of the supply voltage; after roughly five time constants it is considered fully charged. Stored energy is W = half x C x V-squared.

Outside a magnet, magnetic flux lines run from the north pole to the south pole (they continue through the magnet's interior from south back to north, forming a closed loop).

Grip a current-carrying conductor with your right hand, thumb pointing in the direction of conventional current flow - your curled fingers show the direction of the magnetic field circling the conductor.

Reluctance is a magnetic circuit's opposition to flux, the magnetic equivalent of electrical resistance. MMF, the driving force that pushes flux through a circuit, equals current x number of turns, measured in ampere-turns.

Hysteresis is the lag between a changing magnetising force and the resulting flux density in a core. Remanence is the magnetism a core retains after the magnetising force has been removed to zero.

The EMF induced in a conductor or coil is proportional to the rate of change of magnetic flux linkage - move a conductor through a field faster, or change the field faster, and more EMF is generated.

An induced current always flows in the direction that opposes the change in flux that created it - this is why induced effects resist motion and conserve energy, and it sets the sign in Faraday's law.

Self inductance is a single coil opposing changes in its own current (unit: henry). Mutual inductance is two magnetically linked coils, where a changing current in one induces an EMF in the other.

Tau = L/R for an inductive circuit - current builds toward its final value following the same 63%-at-one-tau, near-full-at-five-tau pattern as an RC circuit's voltage.

Fleming's left-hand rule gives the force (and rotation) direction in a motor; Fleming's right-hand rule gives the induced EMF direction in a generator. A motor's back EMF opposes the applied armature current, limiting it as speed rises; a generator's commutator converts the AC induced in the rotating armature into DC output.

RMS (root-mean-square) value = 0.707 x peak value for a sine wave. It represents the equivalent DC value that delivers the same heating/power effect, which is why AC voltages and currents are normally quoted as RMS.

Average value (over a half cycle) = 0.637 x peak value. The ratio of RMS to average, called the form factor, works out to about 1.11 for a pure sine wave.

T = 1/f - periodic time is the time for one complete cycle of an AC waveform, and is simply the reciprocal of frequency.

Most aircraft AC electrical systems run at 400 Hz rather than 50/60 Hz mains frequency, because the higher frequency allows transformers, motors and generators to be built smaller and lighter for a given power rating.

In a capacitor, current leads voltage by 90 degrees - the capacitor must charge (current flows) before its voltage can rise to follow.

In an inductor, current lags voltage by 90 degrees - the coil's back EMF opposes the immediate build-up of current as the applied voltage first rises. Remember 'CIVIL': in a Capacitor, I leads V; in an Inductor, V leads I.

XL = 2 x pi x f x L - an inductor's opposition to AC current rises as frequency increases, because faster current changes induce a larger opposing back EMF.

XC = 1 / (2 x pi x f x C) - a capacitor's opposition to AC current falls as frequency increases, because it has less time to fully charge and discharge each cycle.

Resonance occurs when XL equals XC, cancelling each other out so the circuit's impedance drops to its minimum value (just R) and current is at its maximum for a given applied voltage.

Impedance Z equals the square root of (R-squared plus X-squared), combining resistance and net reactance. Power factor = cos(phi) = R/Z, showing how much of the apparent power actually does useful (real) work.

At higher AC frequencies, current tends to crowd toward the outer surface of a conductor rather than flow evenly through its whole cross-section, which increases the conductor's effective resistance.

Vp/Vs = Np/Ns - the ratio of primary to secondary voltage matches the ratio of primary to secondary turns. For an ideal transformer, power is conserved, so Vp x Ip = Vs x Is, meaning a step-up in voltage means a step-down in current, and vice versa.

Eddy current loss comes from circulating currents induced within the core itself, and is reduced by using a laminated (thin, insulated-sheet) core. Hysteresis loss comes from repeatedly re-magnetising the core each cycle, and is reduced by choosing a soft magnetic core material with a narrow hysteresis loop.

A low-pass filter passes frequencies below its cutoff; a high-pass filter passes frequencies above its cutoff; a band-pass filter passes only a range between two cutoffs; a band-stop (notch) filter rejects only that range.

In a star connection, line voltage = root-3 x phase voltage while line current equals phase current. In a delta connection, line voltage equals phase voltage while line current = root-3 x phase current.