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ITI Mechanic Auto Electrical & Electronics (AITT Theory) study materials
ITI Mechanic Auto Electrical & Electronics (AITT Theory) study resources

ITI Mechanic Auto Electrical & Electronics (AITT Theory) practice questions

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Question 1Trade Safety, Tools, Measuring Instruments and Workshop Practice

While servicing a 12 V automotive battery, which personal protective equipment is most important to protect the technician from electrolyte splash during top-up?

  1. Leather welding gloves and a face shield
  2. Cotton hand gloves and a dust mask
  3. Ear plugs and safety shoes
  4. Chemical splash goggles and acid-resistant gloves Correct answer.

Explanation

Battery electrolyte is dilute sulphuric acid, so eye and hand protection must resist chemical splash. Chemical splash goggles seal around the eyes and acid-resistant gloves protect the hands during top-up and terminal cleaning. Leather, cotton and general PPE do not resist acid penetration.

Question 2Trade Safety, Tools, Measuring Instruments and Workshop Practice

A 12 V automotive battery is being boost-charged from a donor battery. Which connection sequence is correct?

  1. Connect negative to negative first, then positive to the battery terminal
  2. Connect both positive and negative to the dead battery first, then to the donor
  3. Connect positive to negative and negative to positive to equalise the cells
  4. Connect positive to positive first, then negative to a good ground away from the battery Correct answer.

Explanation

The positive leads are joined first, then the final negative connection is made to a chassis ground remote from the battery. This keeps any spark away from hydrogen gas venting at the battery. Reversing polarity or making the last connection at the battery risks explosion and electronic damage.

Question 3Trade Safety, Tools, Measuring Instruments and Workshop Practice

Which instrument is used to measure the specific gravity of battery electrolyte?

  1. Hydrometer Correct answer.
  2. Vernier caliper
  3. Multimeter
  4. Micrometer

Explanation

A hydrometer floats a weighted bulb in the electrolyte and reads specific gravity directly, which indicates state of charge. A fully charged cell reads around 1.260 to 1.280 at 25 degrees Celsius. Electrical and dimensional instruments cannot measure electrolyte density.

Question 4Trade Safety, Tools, Measuring Instruments and Workshop Practice

While using a digital multimeter to measure current drawn by a starter motor, the meter is set to the 10 A range. What is the correct way to connect it?

  1. In series with the circuit, using the high-current terminal Correct answer.
  2. Across the battery posts with the meter on the ohms range
  3. In parallel across the starter terminals, using the common and volts terminals
  4. In parallel with the starter solenoid winding

Explanation

An ammeter must carry the circuit current, so it is connected in series and on the terminal rated for that current. The 10 A socket and range are used because starter current exceeds the low-current fused input. Parallel connection of an ammeter shorts the supply and blows the meter fuse.

Question 5Trade Safety, Tools, Measuring Instruments and Workshop Practice

A technician must measure the diameter of an armature commutator to check for ovality. Which measuring tool gives the required precision?

  1. Steel rule
  2. Try square
  3. Outside micrometer Correct answer.
  4. Feeler gauge

Explanation

Commutator ovality is judged in thousandths of a millimetre, which requires an outside micrometer reading to 0.01 mm or better. A steel rule, try square or feeler gauge cannot resolve diameter changes of that order. Measuring at several points reveals out-of-roundness.

Question 6Trade Safety, Tools, Measuring Instruments and Workshop Practice

A vernier caliper main scale reads 24 mm and the 10th vernier division coincides with a main scale line. If the least count is 0.02 mm, what is the reading?

  1. 25.00 mm
  2. 24.20 mm Correct answer.
  3. 24.02 mm
  4. 24.10 mm

Explanation

The vernier reading is the coinciding division multiplied by the least count, so 10 times 0.02 mm equals 0.20 mm. Adding this to the 24 mm main scale reading gives 24.20 mm. The least count is applied once per coinciding division, not once overall.

Question 7Trade Safety, Tools, Measuring Instruments and Workshop Practice

Before using a torque wrench to tighten cylinder head bolts to a specified figure, what is the correct preliminary step?

  1. Set the wrench above the specified torque to allow for friction
  2. Apply thread-locking compound to the wrench ratchet
  3. Check that the wrench is calibrated and set it to the specified torque Correct answer.
  4. Loosen the lock nut and leave the scale free

Explanation

A torque wrench must be within calibration and set to the specified figure so the fastener receives the designed clamp load. Setting it higher to compensate for friction over-torques the bolt and can distort the head. The scale lock must be engaged after setting.

Question 8Trade Safety, Tools, Measuring Instruments and Workshop Practice

Which fire extinguisher is appropriate for a fire in an energised electrical panel in the auto electrical workshop?

  1. Wet chemical extinguisher
  2. Carbon dioxide extinguisher Correct answer.
  3. Water extinguisher
  4. Foam extinguisher

Explanation

Carbon dioxide is a clean, non-conductive agent suitable for energised electrical equipment and leaves no residue. Water, foam and wet chemical agents conduct electricity and can cause shock to the operator. The supply should still be isolated as soon as it is safe.

Question 9Trade Safety, Tools, Measuring Instruments and Workshop Practice

When lifting a heavy starter motor from a bench, which practice protects the technician's back?

  1. Hold the load at arm's length to keep it clear of the body
  2. Keep the legs straight and bend at the waist
  3. Bend the knees, keep the load close and lift with the leg muscles Correct answer.
  4. Twist the trunk while lifting to swing the load aside

Explanation

Bending the knees and holding the load close keeps the centre of gravity near the spine and uses the strong leg muscles. Straight-leg lifting and twisting place high compressive and shear loads on the lumbar spine. Holding the load away from the body multiplies the moment on the back.

Question 10Trade Safety, Tools, Measuring Instruments and Workshop Practice

A bench grinder is used to dress the tip of a screwdriver. What is the correct safety adjustment before grinding?

  1. Grind on the side face of the wheel
  2. Set the tool rest within about 2 mm of the wheel and the spark guard close to the wheel Correct answer.
  3. Remove the spark guard so the sparks fly clear
  4. Leave the tool rest wide so the tool can be angled freely

Explanation

The tool rest should sit within roughly 2 mm of the wheel face and the spark guard close to the wheel so the workpiece cannot be drawn into the gap. Grinding on the side of a straight wheel can burst it. Guards must never be removed.

Question 11Trade Safety, Tools, Measuring Instruments and Workshop Practice

Which tool is correct for removing a circlip retaining the brush holder in an alternator?

  1. Circlip pliers with pins matching the clip holes Correct answer.
  2. Cold chisel
  3. Adjustable spanner
  4. Long-nose pliers

Explanation

Circlip pliers engage the clip eyes and expand or contract the clip evenly without deforming it. Long-nose pliers slip out of the holes and can bend the clip, while spanners and chisels do not fit the clip at all. Using the wrong tool damages the groove and the component.

Question 12Trade Safety, Tools, Measuring Instruments and Workshop Practice

Why is a puller preferred over a hammer for removing a tight alternator pulley or bearing?

  1. It allows the part to be heated with a flame during removal
  2. It avoids the need for any penetrating oil
  3. It applies a controlled axial force without shock loads to the shaft and bearings Correct answer.
  4. It is quicker to use than a hammer in all cases

Explanation

A puller draws the part off along its axis with a steady force, so the shaft, bearing races and windings are not shock-loaded. Hammer blows can brinell bearing races and crack insulation. Penetrating oil and, where permitted, gentle warming are still useful aids.

Question 13Trade Safety, Tools, Measuring Instruments and Workshop Practice

A soldering iron is used to repair a wiring harness joint. Which practice produces a sound electrical joint?

  1. Melt solder onto the iron tip and carry it to the joint
  2. Apply flux only after the solder has cooled
  3. Clean and tin the iron, heat the joint and apply solder to the joint, not the iron Correct answer.
  4. Use a dry iron tip at low temperature to avoid burning the wire

Explanation

A clean, tinned tip transfers heat efficiently, and solder fed into the heated joint wets both surfaces to form a proper intermetallic bond. Carrying solder on the tip gives a cold, poorly wetted joint. Flux is applied before soldering to remove oxides.

Question 14Trade Safety, Tools, Measuring Instruments and Workshop Practice

A crimping tool is used to terminate a wire in an insulated connector. Which condition indicates a correct crimp?

  1. The barrel is flattened so far that the wire can be pulled out easily
  2. The wire is held only by the insulation sleeve
  3. The conductor strands are fully inside the barrel and the insulation is not cut through Correct answer.
  4. The insulation is stripped back so far that bare wire extends past the barrel

Explanation

A correct crimp encloses all conductor strands in the metal barrel and deforms it into a gas-tight joint, while the insulation remains intact. Wire gripped only by the sleeve or easily pulled out indicates a failed crimp. Bare wire beyond the barrel risks short circuits.

Question 15Trade Safety, Tools, Measuring Instruments and Workshop Practice

A wiring harness is being routed through a body panel. Which practice best prevents future electrical faults?

  1. Route the harness alongside the exhaust pipe for protection
  2. Fit a rubber grommet in the hole and secure the harness with clips at regular intervals Correct answer.
  3. Pull the harness tight to keep it out of the way
  4. Leave the harness loose so it can move freely

Explanation

A grommet protects the insulation from the sharp panel edge and regular clipping prevents flexing and chafing. A taut harness or an unsecured one abrades against metal and fails. Heat from the exhaust hardens insulation and causes cracking.

Question 16Trade Safety, Tools, Measuring Instruments and Workshop Practice

A lead-acid battery is stored in the workshop before fitment. Which storage condition keeps it in the best condition?

  1. A warm place next to the charger to keep it warm
  2. Directly on a concrete floor in a sealed cupboard
  3. Lying on its side to save shelf space
  4. A cool, dry, well-ventilated place on a shelf, kept charged Correct answer.

Explanation

Cool, dry, ventilated storage slows self-discharge and grid corrosion, and periodic charging keeps the plates from sulphating. Warm storage accelerates self-discharge and water loss. Sealed or tipped storage risks electrolyte spillage and gas accumulation.

Question 17Trade Safety, Tools, Measuring Instruments and Workshop Practice

An insulation resistance tester is used to check a motor winding to earth. Which statement about the test is correct?

  1. The circuit must be isolated and the winding discharged before the test is applied Correct answer.
  2. The tester is connected across the battery to measure voltage
  3. The tester is used with the circuit live to check under load
  4. The winding must be connected to earth at both ends during the test

Explanation

An insulation tester applies a high DC voltage, so the circuit must be isolated and any stored charge discharged before and after testing. Testing a live circuit is dangerous and gives meaningless results. Earthing both ends would short the test voltage.

Question 18Trade Safety, Tools, Measuring Instruments and Workshop Practice

A technician must check the free length of a coil spring and compare it with the specification. Which instrument and method are appropriate?

  1. Micrometer, measuring the wire diameter only
  2. Torque wrench, measuring the force needed to compress it
  3. Vernier caliper or steel rule, measuring from a flat surface with the spring unloaded Correct answer.
  4. Feeler gauge inserted between the coils

Explanation

Free length is an axial dimension, so it is measured with the spring uncompressed on a flat surface using a rule or caliper. A micrometer measures wire diameter, not overall length. A feeler gauge measures gaps and a torque wrench measures applied torque.

Question 19Trade Safety, Tools, Measuring Instruments and Workshop Practice

Which precaution is essential before working on the supplemental restraint system of a vehicle?

  1. Strike the steering wheel pad to check that the sensor is free
  2. Isolate the battery and wait the manufacturer's specified time for the capacitor to discharge Correct answer.
  3. Disconnect the airbag connector while the ignition is on
  4. Test the airbag circuit with a low-resistance ohmmeter

Explanation

The SRS has a backup capacitor that can fire the airbag for a period after the battery is disconnected, so the specified wait is mandatory. Testing with an ohmmeter or disturbing connectors while live can deploy the airbag. Mechanical shock to the module is also dangerous.

Question 20Trade Safety, Tools, Measuring Instruments and Workshop Practice

A technician is checking a 12 V circuit for a voltage drop. Which condition indicates excessive resistance in a cable or connection?

  1. A measurable voltage drop across the conductor while the circuit is loaded Correct answer.
  2. Zero volts across the conductor while the circuit is loaded
  3. Continuity between the conductor and the body earth
  4. Full battery voltage at the component with the circuit open

Explanation

Voltage drop testing is done with the circuit loaded, because resistance only shows as a drop when current flows. A healthy conductor shows almost zero volts across it. Full battery voltage at an open circuit shows supply is present, not that resistance is excessive.

Question 21Basic Electricity, Magnetism and Electrical Units

In an automotive 12 V circuit, what does the unit 'ampere' actually measure?

  1. The rate of flow of electric charge past a point Correct answer.
  2. The opposition offered by a conductor to current
  3. The potential difference between two terminals
  4. The quantity of charge stored in a battery

Explanation

One ampere is defined as a flow of one coulomb of charge per second, so the ampere is a measure of current, i.e. the rate of charge movement. Voltage (volt) describes potential difference, resistance (ohm) describes opposition to current, and stored charge is measured in ampere-hours or coulombs.

Question 22Basic Electricity, Magnetism and Electrical Units

A starter motor draws 200 A from a 12 V battery for 3 seconds. What charge passes through the circuit?

  1. 600 C Correct answer.
  2. 0.6 C
  3. 2400 C
  4. 66.7 C

Explanation

Charge equals current multiplied by time, Q = I × t = 200 A × 3 s = 600 coulombs. This follows directly from the definition of the ampere as one coulomb per second.

Question 23Basic Electricity, Magnetism and Electrical Units

Which statement correctly describes the relationship between e.m.f. and terminal voltage of a battery supplying current?

  1. Terminal voltage is independent of the current drawn
  2. Terminal voltage is always greater than the e.m.f.
  3. Terminal voltage equals e.m.f. minus the internal volt drop Correct answer.
  4. Terminal voltage equals e.m.f. plus the internal volt drop

Explanation

The e.m.f. is the total energy per unit charge produced by the source. When current flows, part of that e.m.f. is lost inside the battery across its internal resistance, so terminal voltage = e.m.f. − (I × r).

Question 24Basic Electricity, Magnetism and Electrical Units

What is the standard unit of electrical resistance and what does one unit represent?

  1. The ohm, equal to one volt per ampere Correct answer.
  2. The watt, equal to one joule per second
  3. The farad, equal to one coulomb per volt
  4. The henry, equal to one weber per ampere

Explanation

Resistance is measured in ohms, and one ohm is the resistance that allows one ampere to flow when one volt is applied (R = V/I). The other units listed measure power, capacitance and inductance respectively.

Question 25Basic Electricity, Magnetism and Electrical Units

A 12 V headlamp bulb has a resistance of 3 Ω. What current does it take?

  1. 9 A
  2. 36 A
  3. 4 A Correct answer.
  4. 0.25 A

Explanation

Ohm's law gives I = V/R = 12 V / 3 Ω = 4 A. Always divide voltage by resistance to obtain current in amperes.

Question 26Basic Electricity, Magnetism and Electrical Units

A 60 W, 12 V automotive lamp is operating at its rated voltage. What current flows through it?

  1. 0.2 A
  2. 5 A Correct answer.
  3. 720 A
  4. 72 A

Explanation

Power equals voltage multiplied by current, so I = P/V = 60 W / 12 V = 5 A. This relationship is used constantly when sizing fuses and wiring for vehicle accessories.

Question 27Basic Electricity, Magnetism and Electrical Units

How much energy does a 24 W reversing lamp consume when it is lit for 30 seconds?

  1. 1440 J
  2. 0.8 J
  3. 720 J Correct answer.
  4. 2.4 J

Explanation

Energy equals power multiplied by time: E = P × t = 24 W × 30 s = 720 joules, because one watt is one joule per second. Keeping units consistent in seconds avoids errors.

Question 28Basic Electricity, Magnetism and Electrical Units

Which material property makes copper preferred over steel for automotive current-carrying conductors?

  1. Lower resistivity, giving less volt drop for the same cross-section Correct answer.
  2. Higher permeability, giving stronger magnetic retention
  3. Lower melting point, giving easier soldering
  4. Higher resistivity with greater mechanical strength

Explanation

Copper has a much lower resistivity than steel, so for a given length and cross-sectional area it produces a smaller resistance and therefore a smaller volt drop and lower heating. Mechanical strength and cost are secondary considerations in harness design.

Question 29Basic Electricity, Magnetism and Electrical Units

A copper cable of fixed length is replaced by one with twice the cross-sectional area. How does its resistance change, all else being equal?

  1. It becomes four times larger
  2. It doubles
  3. It halves Correct answer.
  4. It stays the same

Explanation

Resistance is inversely proportional to cross-sectional area (R = ρL/A). Doubling the area therefore halves the resistance, which is why heavier gauge cable is used for high-current circuits such as starter feeds.

Question 30Basic Electricity, Magnetism and Electrical Units

What happens to the resistance of a typical metallic conductor such as copper when its temperature rises?

  1. It increases Correct answer.
  2. It remains constant
  3. It falls to zero at 100 °C
  4. It decreases steadily

Explanation

In metals, higher temperature increases lattice vibration, which scatters drifting electrons more and raises resistance. This is why a hot filament has a far higher resistance than the same lamp when cold.

Question 31Basic Electricity, Magnetism and Electrical Units

Which rule gives the direction of the magnetic field around a straight current-carrying conductor?

  1. Fleming's right-hand rule
  2. Lenz's law
  3. The right-hand grip rule Correct answer.
  4. Fleming's left-hand rule

Explanation

The right-hand grip rule states that if the thumb points along the conventional current, the curled fingers show the direction of the circular magnetic field. Fleming's rules relate to force and induced current in motors and generators.

Question 32Basic Electricity, Magnetism and Electrical Units

What is the unit of magnetic flux density, and what does one unit mean?

  1. The ampere-turn, one magnetomotive force per turn
  2. The weber, one volt-second of total flux
  3. The tesla, one newton per ampere-metre of conductor Correct answer.
  4. The henry, one weber per ampere of current

Explanation

Magnetic flux density B is measured in tesla, where one tesla produces a force of one newton on a one-metre conductor carrying one ampere at right angles to the field. The weber measures total flux and the henry measures inductance.

Question 33Basic Electricity, Magnetism and Electrical Units

A conductor of length 0.4 m carries 5 A at right angles to a magnetic field of flux density 0.3 T. What force acts on it?

  1. 0.6 N Correct answer.
  2. 6 N
  3. 0.06 N
  4. 1.5 N

Explanation

The force on a conductor is F = B × I × L × sin θ, and here θ is 90° so sin θ = 1. Thus F = 0.3 T × 5 A × 0.4 m = 0.6 N.

Question 34Basic Electricity, Magnetism and Electrical Units

According to Faraday's law, what determines the magnitude of an induced e.m.f. in a coil?

  1. The steady value of the magnetic flux linking the coil
  2. The direction of the current in the coil
  3. The rate of change of magnetic flux linkage Correct answer.
  4. The resistance of the coil wire only

Explanation

Faraday's law states that the induced e.m.f. is proportional to the rate of change of flux linkage, so a faster change or more turns gives a larger e.m.f. A constant flux, however large, induces nothing.

Question 35Basic Electricity, Magnetism and Electrical Units

Lenz's law explains which feature of an induced e.m.f.?

  1. It is independent of the number of turns
  2. It exists only in conductors moving parallel to the field
  3. Its direction always opposes the change producing it Correct answer.
  4. Its magnitude increases with coil resistance

Explanation

Lenz's law states that the induced e.m.f. drives a current whose magnetic effect opposes the change in flux that created it, which is a direct consequence of energy conservation. It fixes the polarity of the induced e.m.f.

Question 36Basic Electricity, Magnetism and Electrical Units

Which quantity is measured in farads in an automotive electronic circuit?

  1. The resistance of a sensor element
  2. The inductance of an ignition coil primary
  3. The magnetic flux in a solenoid
  4. The capacitance of a suppression capacitor Correct answer.

Explanation

The farad is the unit of capacitance, defined as one coulomb stored per volt applied. Capacitors are used in vehicles for radio interference suppression and for smoothing supply voltage.

Question 37Basic Electricity, Magnetism and Electrical Units

A capacitor of 470 µF is charged to 12 V. What charge does it store?

  1. 25.5 mC
  2. 39.2 mC
  3. 0.039 C
  4. 5.64 mC Correct answer.

Explanation

Charge equals capacitance multiplied by voltage: Q = C × V = 470 × 10⁻⁶ F × 12 V = 5.64 × 10⁻³ C, i.e. 5.64 mC. Remember to convert microfarads to farads before calculating.

Question 38Basic Electricity, Magnetism and Electrical Units

In a series circuit of three resistors, which quantity is the same through every component?

  1. The current Correct answer.
  2. The resistance of each resistor
  3. The power dissipated in each resistor
  4. The voltage across each resistor

Explanation

A series circuit offers only one path, so the same current must pass through every element. Voltage, power and resistance can all differ between the individual components.

Question 39Basic Electricity, Magnetism and Electrical Units

Two resistors of 6 Ω and 3 Ω are connected in parallel. What is the equivalent resistance?

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

Explanation

For two resistors in parallel, R = (R1 × R2)/(R1 + R2) = (6 × 3)/(6 + 3) = 18/9 = 2 Ω. The result is always smaller than the smallest individual resistor.

Question 40Basic Electricity, Magnetism and Electrical Units

A 12 V supply feeds two 6 Ω resistors in series. What is the voltage across one of them?

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

Explanation

Total resistance is 12 Ω, so the current is 12 V / 12 Ω = 1 A. Each 6 Ω resistor then drops I × R = 1 A × 6 Ω = 6 V, and the two drops add to the supply voltage.

Question 41Basic Electricity, Magnetism and Electrical Units

What is the RMS value of a sinusoidal alternating voltage whose peak value is 170 V?

  1. 340 V
  2. 85 V
  3. 170 V
  4. 120 V Correct answer.

Explanation

For a sine wave, V(rms) = V(peak)/√2 = 170/1.414 ≈ 120 V. The RMS value is the steady d.c. value that would produce the same heating effect.

Question 42Basic Electricity, Magnetism and Electrical Units

In a purely capacitive a.c. circuit, what is the phase relationship between the current and the applied voltage?

  1. Current lags the voltage by 45°
  2. Current leads the voltage by 90° Correct answer.
  3. Current lags the voltage by 90°
  4. Current is in phase with the voltage

Explanation

A capacitor charges fastest when the applied voltage is changing most rapidly, so the current reaches its maximum a quarter cycle before the voltage. This gives a 90° lead of current over voltage.

Question 43Basic Electricity, Magnetism and Electrical Units

Why is a laminated iron core used in an ignition coil or transformer?

  1. To insulate the primary from the secondary
  2. To raise the saturation flux density of iron
  3. To increase the resistance of the winding
  4. To reduce eddy-current losses in the core Correct answer.

Explanation

Laminations interrupt the paths available for circulating eddy currents, greatly reducing the power wasted as heat in the core. The thin oxide layers between laminations provide the necessary insulation.

Question 44Basic Electricity, Magnetism and Electrical Units

Which instrument connection is correct when measuring the current drawn by a fuel pump?

  1. Voltmeter in series with the pump circuit
  2. Ohmmeter across the pump with power on
  3. Ammeter in series with the pump circuit Correct answer.
  4. Ammeter in parallel with the pump

Explanation

An ammeter has very low resistance and must carry the circuit current, so it is connected in series. Connecting it in parallel would short the supply and could destroy the meter or blow the fuse.

Question 45Batteries, Charging Systems and Starting Systems

In a lead-acid battery, what is the active material of the positive plate after full formation charging?

  1. Antimony-lead alloy
  2. Lead dioxide (PbO2) Correct answer.
  3. Lead sulphate (PbSO4)
  4. Sponge lead (Pb)

Explanation

During formation and charging the positive plate is converted to lead dioxide, a dark brown porous material, while the negative plate becomes sponge lead. On discharge both plates convert to lead sulphate. Recognising these states explains capacity loss and sulphation faults.

Question 46Batteries, Charging Systems and Starting Systems

A 12 V automotive battery is described as having six cells. What is the nominal voltage of each cell?

  1. 6.0 V
  2. 2.0 V
  3. 2.1 V Correct answer.
  4. 1.2 V

Explanation

Each lead-acid cell produces about 2.1 V at full charge, so six cells in series give the familiar 12.6 V open-circuit reading of a nominal 12 V battery. The nominal 2 V per cell figure is a rounded design value. This is why a healthy rested battery reads above 12 V.

Question 47Batteries, Charging Systems and Starting Systems

Which test determines the state of charge of a battery most reliably without applying a heavy load?

  1. Battery case leakage test
  2. Hydrometer reading of electrolyte specific gravity Correct answer.
  3. Starter current draw test
  4. Alternator ripple voltage test

Explanation

Specific gravity of the electrolyte falls as the battery discharges, so a hydrometer reading corrected for temperature indicates state of charge directly on serviceable batteries. Open-circuit voltage gives similar information but is coarser. Load and ripple tests check condition and charging, not charge level.

Question 48Batteries, Charging Systems and Starting Systems

What is the purpose of the separator in a lead-acid battery cell?

  1. To conduct current between adjacent cells
  2. To support the terminal posts
  3. To prevent direct contact between positive and negative plates while allowing ion flow Correct answer.
  4. To vent explosive gases from the cell

Explanation

The separator is a porous insulating sheet placed between plates of opposite polarity so they cannot touch and short-circuit, while its porosity lets electrolyte and ions pass. Modern separators are often microporous polyethylene envelopes. Cell connectors, not separators, carry current between cells.

Question 49Batteries, Charging Systems and Starting Systems

Which component converts the alternating current produced in the alternator stator into direct current for the vehicle system?

  1. Rotor field winding
  2. Voltage regulator
  3. Slip ring assembly
  4. Rectifier bridge Correct answer.

Explanation

The three-phase AC induced in the stator windings is fed through a six-diode rectifier bridge, which allows current to flow to the battery in one direction only. The regulator controls field current and therefore output voltage. Slip rings and the rotor winding only supply the rotating field.

Question 50Batteries, Charging Systems and Starting Systems

In a starter motor, what is the function of the overrunning clutch in the drive assembly?

  1. To transmit torque to the flywheel ring gear while allowing the pinion to overrun when the engine starts Correct answer.
  2. To hold the armature in the field frame
  3. To move the pinion into mesh with the ring gear
  4. To reduce the current drawn by the starter

Explanation

The overrunning clutch, commonly a roller-type one-way clutch, locks in the cranking direction to drive the ring gear. Once the engine fires and spins faster than the starter, the clutch freewheels so the armature is not over-revved and damaged. Pinion engagement is performed by the solenoid or a lever.