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EASA Module 3 study materials
EASA Module 3 study resources

EASA Module 3 practice questions

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Question 1Electron Theory

What is the electric charge carried by a single electron?

  1. +1.602 × 10⁻¹⁹ C
  2. −9.109 × 10⁻³¹ C
  3. −1.602 × 10⁻²² C
  4. −1.602 × 10⁻¹⁹ C Correct answer.

Explanation

Charge is quantised, and the elementary charge has a magnitude of 1.602 × 10⁻¹⁹ C. An electron carries this amount with a negative sign, while a proton carries it with a positive sign.

Question 2Electron Theory

In a copper wire connected to a battery, conventional current is taken to flow in which direction?

  1. From the positive terminal to the negative terminal, in the same direction as electron drift
  2. From the positive terminal to the negative terminal, opposite to electron drift Correct answer.
  3. From the negative terminal to the positive terminal, in the same direction as electron drift
  4. Alternating evenly between both terminals at the supply frequency

Explanation

Conventional current was defined historically as flow from the positive terminal to the negative terminal. Electrons carry negative charge, so their actual drift is in the opposite direction, from negative to positive.

Question 3Electron Theory

Electrons occupying the outermost shell of an atom are referred to as:

  1. valence electrons Correct answer.
  2. free electrons
  3. isotopes
  4. bound electrons

Explanation

The outermost occupied shell is the valence shell, and its electrons govern the atom's electrical and chemical behaviour. They are named valence electrons after that shell.

Question 4Electron Theory

A pure semiconductor such as silicon has how many electrons in its outermost shell?

  1. Four Correct answer.
  2. Three
  3. Two
  4. One

Explanation

Silicon and germanium are group IV elements, so each atom has four valence electrons. This half-filled outer shell is what gives the material its intermediate conductivity.

Question 5Electron Theory

Ionisation of an atom occurs when:

  1. the nucleus emits a neutron and becomes unstable
  2. the atom's electron shells collapse into the nucleus
  3. an electron is added or removed, leaving a net charge Correct answer.
  4. the atom gains protons from a neighbouring atom

Explanation

An atom normally has equal numbers of protons and electrons. Ionisation upsets this balance by adding or removing electrons, leaving a net charge on the atom while the nucleus itself is unchanged.

Question 6Electron Theory

Applying the 2n² rule, what is the maximum number of electrons that the third shell (n = 3) can hold?

  1. 8
  2. 18 Correct answer.
  3. 32
  4. 6

Explanation

The maximum occupancy of a shell is given by 2n². Substituting n = 3 gives 2 × 9, which is 18 electrons.

Question 7Electron Theory

According to Coulomb's law, the electrostatic force between two point charges is inversely proportional to:

  1. the square of their separation Correct answer.
  2. the product of the two charges
  3. the cube of their separation
  4. the distance between them

Explanation

Coulomb's law gives F = kQ₁Q₂/r². The force therefore grows with the product of the charges and falls with the square of the distance separating them.

Question 8Electron Theory

A free electron in a metal is one that:

  1. loses its charge while drifting through the metal
  2. is detached from its atom and free to move Correct answer.
  3. is held tightly to its parent atom even under an EMF
  4. is confined to the nucleus of the atom

Explanation

In a metallic lattice the outer electrons are shared by the whole structure rather than belonging to one atom. These detached electrons are the free electrons that drift under an applied EMF and carry the current.

Question 9Electron Theory

Thermionic emission is the release of electrons from a metal surface by:

  1. bombarding the surface with ions
  2. immersing the metal in an electrolyte
  3. heating the metal Correct answer.
  4. applying a strong electric field

Explanation

Heating raises the thermal energy of the valence electrons until some exceed the work function and escape the surface. This effect is the source of electrons in a thermionic valve.

Question 10Electron Theory

In the photoelectric effect, electrons are emitted from a surface when:

  1. the surface is heated above its melting point
  2. a magnetic field is swept across the surface
  3. the surface is placed in a strong electrolyte
  4. radiation of sufficiently high frequency falls on it Correct answer.

Explanation

Each photon delivers energy hf to an electron. Emission takes place only when that photon energy exceeds the work function of the material, which is why frequency rather than mere intensity is the deciding factor.

Question 11Electron Theory

For a normal current in a copper conductor, the drift velocity of the conduction electrons is of the order of:

  1. a few millimetres per second Correct answer.
  2. 2 × 10⁵ m/s
  3. 3 × 10⁸ m/s
  4. a few hundred metres per second

Explanation

Electrons move at high random thermal speeds, but the small superimposed drift caused by the applied field is typically only of the order of a millimetre per second. The electrical signal appears almost instantly because the field propagates along the wire, not because electrons travel quickly.

Question 12Electron Theory

As the temperature of a pure metal conductor rises, its resistance:

  1. falls, because heating releases more free electrons
  2. stays constant, since the number of free electrons is fixed
  3. rises, because the hotter lattice scatters electrons more Correct answer.
  4. falls, because heating makes the lattice more ordered

Explanation

In a metal the number of free electrons is essentially fixed by the material. Raising the temperature increases lattice vibration, so electrons collide more frequently and resistivity rises, giving a positive temperature coefficient.

Question 13Electron Theory

A glass rod rubbed with silk becomes positively charged because:

  1. electrons are transferred from the glass to the silk Correct answer.
  2. it gains protons from the silk
  3. electrons move from the silk onto the glass
  4. the silk loses all of its bound electrons

Explanation

Rubbing brings the surfaces into close contact and allows electrons to transfer. Silk holds electrons more strongly than glass, so the glass gives up electrons and is left with a net positive charge while the silk becomes negative.

Question 14Electron Theory

The electromotive force of a source is defined as:

  1. the maximum current the source can deliver into a short circuit
  2. the potential difference across the internal resistance
  3. the force exerted on a unit charge at the terminals
  4. the energy converted to electrical form per unit charge Correct answer.

Explanation

EMF is the energy per unit charge that the source converts from some other form into electrical form, and it is measured in volts. Despite its name, it is not a mechanical force.

Question 15Electron Theory

Below its critical temperature, a superconducting material:

  1. has a resistance that falls gradually to about half its room-temperature value
  2. behaves as a perfect insulator for direct current
  3. shows a negative temperature coefficient only above the critical point
  4. carries current with no measurable resistance Correct answer.

Explanation

At the critical temperature the material changes state and its resistance drops abruptly to zero. A current then continues to flow without any applied EMF for as long as the material stays cold.

Question 16Electron Theory

One ampere is defined as the current that transfers:

  1. one coulomb per minute past a point
  2. one joule of energy per second past a point
  3. one coulomb per second past a point Correct answer.
  4. one volt across one ohm in one minute

Explanation

Current is the rate of flow of electric charge. One ampere corresponds to the transfer of one coulomb of charge past a given point in one second.

Question 17Electron Theory

In a neutral atom, the number of electrons is equal to:

  1. the number of protons in the nucleus Correct answer.
  2. the number of protons plus the number of neutrons
  3. the number of neutrons in the nucleus
  4. the mass number of the element

Explanation

Neutrality requires the total negative charge to balance the total positive charge. Since each electron and each proton carries one elementary charge, the electron count equals the proton count, which is the atomic number.

Question 18Electron Theory

Which statement best describes an electrical insulator?

  1. It has many free electrons that move easily under an applied EMF
  2. Its outer electrons are tightly bound, so few are free to move Correct answer.
  3. Its valence shell is exactly half full of electrons
  4. Its resistance falls sharply as its temperature increases

Explanation

In an insulator the valence electrons are held firmly to their atoms, so virtually none are available as charge carriers. This is why negligible current flows even when a considerable EMF is applied.

Question 19Static Electricity and Conduction

Which quantity is measured in coulombs?

  1. Capacitance
  2. Potential difference
  3. Electric charge Correct answer.
  4. Electric current

Explanation

The coulomb is the SI unit of electric charge and corresponds to the charge of about 6.24 × 10^18 electrons. Current is the rate of flow of charge, potential difference is energy per unit charge, and capacitance describes charge stored per volt.

Question 20Static Electricity and Conduction

A plastic panel becomes charged by friction with a dry cloth and, as a result, loses electrons. The panel is:

  1. Negatively charged
  2. Positively charged Correct answer.
  3. Electrically neutral
  4. Polarised but uncharged

Explanation

Electrons carry negative charge, so a body that loses electrons is left with a net positive charge. Friction transfers electrons between the two surfaces, while the much heavier positive ions stay fixed in the material.

Question 21Static Electricity and Conduction

Which of these materials is a good conductor of electricity?

  1. Hard rubber
  2. Dry air
  3. Glass
  4. Copper Correct answer.

Explanation

Metals such as copper contain free electrons that drift under an applied field, so they conduct well. Glass, dry air and hard rubber have very few mobile charge carriers and behave as insulators.

Question 22Static Electricity and Conduction

Two point charges in air, separated by a distance d, repel each other with a force F. If the separation is increased to 2d, the force becomes:

  1. F/2
  2. F/4 Correct answer.
  3. 2F
  4. 4F

Explanation

Coulomb's law states that the force between two point charges is inversely proportional to the square of their separation. Doubling the distance therefore multiplies the force by 1/2², that is by one quarter.

Question 23Static Electricity and Conduction

The electric field strength at a point in an electric field is defined as:

  1. the work done in moving unit charge between two points
  2. the force per unit positive charge at that point Correct answer.
  3. the energy per unit charge at that point
  4. the total charge enclosed by a closed surface

Explanation

Field strength is force divided by charge, so it is measured in newtons per coulomb, which is equivalent to volts per metre. The work done per unit charge between two points is the potential difference, and the energy per unit charge at a point is the potential.

Question 24Static Electricity and Conduction

An isolated hollow conducting sphere carries a net electrostatic charge. In equilibrium, the electric field at a point in the empty cavity inside the sphere is:

  1. zero Correct answer.
  2. greatest at the centre of the cavity
  3. constant and directed radially outwards
  4. equal to the field at the outer surface

Explanation

In electrostatic equilibrium the charge resides on the outer surface of the conductor, and there is no field within the conducting material or in an empty cavity. Any field inside would drive the free charges until it was cancelled.

Question 25Static Electricity and Conduction

The charge on an isolated, smooth conducting sphere in electrostatic equilibrium is distributed so that the surface charge density is:

  1. zero over the whole surface
  2. uniform over the whole surface Correct answer.
  3. greatest at the top of the sphere
  4. greatest at the bottom of the sphere

Explanation

Every point on a smooth sphere is geometrically identical, so mutual repulsion spreads the charge evenly and the density is the same everywhere. The density becomes greater only where the curvature is sharper, as at points and edges.

Question 26Static Electricity and Conduction

Before refuelling, the aircraft should be bonded to the fuel supply vehicle in order to:

  1. provide a return path for the aircraft's electrical system
  2. equalise potential so that no spark can occur Correct answer.
  3. prevent corrosion inside the fuel tanks
  4. allow the fuel to flow more quickly

Explanation

Fuel flow generates static charge, and any potential difference between the aircraft and the bowser could produce a spark near fuel vapour. The bonding lead brings both to the same potential so that no spark can jump between them.

Question 27Static Electricity and Conduction

A sensitive avionics unit is protected from external electrostatic fields by housing it in:

  1. a ferrite bead on the supply lead
  2. a thick moulded plastic housing
  3. an insulating gasket around each connector
  4. a continuous earthed metal enclosure Correct answer.

Explanation

A continuous conducting enclosure acts as a Faraday cage: charge on its outer surface produces no field within the space it encloses. The enclosure must be earthed and free of gaps to be effective.

Question 28Static Electricity and Conduction

The purpose of the static dischargers fitted to the trailing edges of an aircraft is to:

  1. act as lightning conductors to route strike current
  2. indicate the build-up of static on the airframe
  3. reduce aerodynamic drag at the trailing edge
  4. release static charge into the air Correct answer.

Explanation

Static dischargers, or wicks, provide sharp points from which accumulated charge leaks into the air by point discharge. This keeps the aircraft's potential low enough to protect sensitive radio and navigation equipment.

Question 29Static Electricity and Conduction

Two identical small conducting spheres carry charges of +6 µC and −2 µC. They are touched together and then separated. The charge on each sphere is now:

  1. +2 µC Correct answer.
  2. +4 µC
  3. −2 µC
  4. 0 µC

Explanation

On contact the charges combine to give a net charge of +4 µC, which is shared equally between two identical spheres, leaving +2 µC on each. Total charge is conserved, but the negative charge partially neutralises the positive one.

Question 30Static Electricity and Conduction

Two point charges separated by a fixed distance experience a force F in air. When they are immersed in a dielectric of relative permittivity 4, the force becomes:

  1. 4F
  2. 2F
  3. F/4 Correct answer.
  4. F

Explanation

Coulomb's law includes the permittivity of the medium, so the force is inversely proportional to permittivity. A relative permittivity of 4 reduces the force to one quarter of its value in air.

Question 31Static Electricity and Conduction

In a copper wire connected to a battery, the electric current is carried by:

  1. electrons travelling along the wire at the speed of light
  2. positive ions drifting towards the negative terminal
  3. free electrons drifting towards the positive terminal Correct answer.
  4. protons and electrons moving in opposite directions

Explanation

Metals conduct through free electrons, which drift towards the positive terminal under the influence of the applied field. The drift speed is very small, although the field is established along the whole wire almost instantly.

Question 32Static Electricity and Conduction

Conduction through an electrolyte differs from conduction in a metal because in an electrolyte:

  1. resistance falls steadily as the electrolyte dries out
  2. ions of both signs move and chemical action occurs Correct answer.
  3. only electrons move, as in a solid metal conductor
  4. charge moves without any movement of ions or matter

Explanation

In an electrolyte the current is carried by positive and negative ions travelling in opposite directions towards the electrodes, where chemical changes take place. Metallic conduction involves electrons only and no transfer of matter.

Question 33Static Electricity and Conduction

A resistor has a resistance of 20 Ω. Its conductance is:

  1. 5 S
  2. 20 S
  3. 0.05 S Correct answer.
  4. 0.5 S

Explanation

Conductance is the reciprocal of resistance, G = 1/R, and is measured in siemens. Thus 1/20 Ω = 0.05 S, which is the same as 50 mS.

Question 34Static Electricity and Conduction

A body carries a net charge of −1.6 µC. Taking the elementary charge as 1.6 × 10⁻¹⁹ C, the number of excess electrons on the body is:

  1. 1 × 10¹⁹
  2. 1 × 10¹⁰
  3. 1.6 × 10¹³
  4. 1 × 10¹³ Correct answer.

Explanation

The number of electrons equals the total charge divided by the elementary charge: 1.6 × 10⁻⁶ divided by 1.6 × 10⁻¹⁹ gives 1 × 10¹³. The negative sign confirms that the charge is due to an excess of electrons.

Question 35Static Electricity and Conduction

Static charge leaks into the surrounding air most readily from a sharp point on a charged conductor because:

  1. air pressure falls sharply near a point
  2. the field there is strongest and ionises the air Correct answer.
  3. the charge density is lowest at a sharp point
  4. the metal is thinnest there so resistance is lowest

Explanation

Charge concentrates where the curvature is greatest, giving a high surface charge density and a strong local field. When the field is strong enough to ionise the air, the resulting ions are repelled away as a point or corona discharge.

Question 36Static Electricity and Conduction

During refuelling, the risk of a static spark is greatest when:

  1. the fuel is highly conductive and flows slowly
  2. the fuel is a poor conductor and flows at high velocity Correct answer.
  3. the surrounding air is very humid
  4. the fuelling hose is bonded to the aircraft and to earth

Explanation

Charge is generated in proportion to flow rate and turbulence, and a low-conductivity fuel cannot shed that charge quickly, so it accumulates in the pipework and tanks. Bonding, and damp air that makes surfaces slightly conductive, both help charge to leak away and so reduce the risk.

Question 37Electrical Terminology

The SI unit of electric charge is the:

  1. volt
  2. coulomb Correct answer.
  3. ampere
  4. farad

Explanation

Charge is measured in coulombs, one coulomb being the quantity of charge carried past a point by a steady current of one ampere in one second. The other named units measure current, potential difference and capacitance respectively.

Question 38Electrical Terminology

In the external circuit of a source, conventional current is taken to flow:

  1. from positive to negative, against electron flow Correct answer.
  2. from positive to negative, the same as electron flow
  3. from negative to positive, the same as electron flow
  4. from negative to positive, against electron flow

Explanation

Conventional current is defined as the movement of positive charge, so it is drawn flowing out of the positive terminal, through the external circuit, and back to the negative terminal. Electrons actually drift the other way, from negative to positive.

Question 39Electrical Terminology

The ohm is equivalent to:

  1. one joule per coulomb
  2. one watt per ampere
  3. one coulomb per second
  4. one volt per ampere Correct answer.

Explanation

Resistance is defined by R = V/I, so one ohm is the resistance of a conductor in which a potential difference of one volt drives a current of one ampere.

Question 40Electrical Terminology

A capacitor marked 0.047 microfarad has a value of:

  1. 4.7 nF
  2. 47 nF Correct answer.
  3. 470 pF
  4. 470 nF

Explanation

There are 1000 nanofarads in a microfarad, so 0.047 microfarad is 0.047 x 1000 = 47 nanofarads.

Question 41Electrical Terminology

The watt is equivalent to:

  1. one joule per second Correct answer.
  2. one coulomb per second
  3. one newton per metre
  4. one volt per coulomb

Explanation

Power is the rate at which energy is transferred, P = W/t, so one watt is one joule of energy converted each second. The same unit is obtained from the product of volts and amperes.

Question 42Electrical Terminology

A potential difference of 12 V is maintained across a 4 ohm resistor. The current through it is:

  1. 16 A
  2. 0.33 A
  3. 48 A
  4. 3 A Correct answer.

Explanation

Ohm's law gives I = V/R, so the current is 12 divided by 4, which is 3 amperes.

Question 43Electrical Terminology

A 24 V DC motor draws a current of 0.5 A. The power it consumes is:

  1. 48 W
  2. 24.5 W
  3. 0.02 W
  4. 12 W Correct answer.

Explanation

Electrical power is the product of voltage and current, so P = 24 x 0.5 = 12 watts.

Question 44Electrical Terminology

Resistors of 6 ohm and 3 ohm are joined in parallel. The equivalent resistance is:

  1. 4.5 ohm
  2. 9 ohm
  3. 18 ohm
  4. 2 ohm Correct answer.

Explanation

For two resistors in parallel, 1/R = 1/6 + 1/3 = 1/2, giving R = 2 ohm. The result must always be smaller than the smallest branch resistance.

Question 45Electrical Terminology

A 100 W lamp is left switched on for 5 hours. The energy it consumes is:

  1. 20 kWh
  2. 500 kWh
  3. 0.5 kWh Correct answer.
  4. 5 kWh

Explanation

Energy equals power multiplied by time; converting to kilowatts gives 0.1 kW x 5 h = 0.5 kWh.

Question 46Electrical Terminology

A sinusoidal supply has an RMS value of 230 V. Its peak value is approximately:

  1. 163 V
  2. 325 V Correct answer.
  3. 460 V
  4. 230 V

Explanation

For a sine wave the peak value equals the RMS value multiplied by the square root of two, so 230 x 1.414 is about 325 volts.

Question 47Electrical Terminology

A waveform repeats at a frequency of 400 Hz. Its periodic time is:

  1. 4 ms
  2. 2.5 ms Correct answer.
  3. 0.4 ms
  4. 25 ms

Explanation

Periodic time is the reciprocal of frequency, T = 1/f = 1/400 s = 0.0025 s, which is 2.5 milliseconds.

Question 48Electrical Terminology

A 10 microfarad capacitor is charged to a potential difference of 50 V. The charge stored is:

  1. 5000 microcoulomb
  2. 0.2 microcoulomb
  3. 500 microcoulomb Correct answer.
  4. 5 microcoulomb

Explanation

Charge is capacitance multiplied by voltage, Q = CV = 10 x 10^-6 x 50 = 500 x 10^-6 coulomb, that is 500 microcoulombs.

Question 49Electrical Terminology

The conductance of an 8 ohm resistor is:

  1. 0.5 S
  2. 0.125 S Correct answer.
  3. 1.25 S
  4. 8 S

Explanation

Conductance is the reciprocal of resistance, G = 1/R, so an 8 ohm resistor has a conductance of 0.125 siemens.

Question 50Electrical Terminology

A battery with an EMF of 12 V and an internal resistance of 1 ohm supplies a current of 2 A. The terminal voltage is:

  1. 6 V
  2. 14 V
  3. 12 V
  4. 10 V Correct answer.

Explanation

The terminal voltage is the EMF minus the internal voltage drop, V = E - Ir = 12 - (2 x 1) = 10 volts.