DGCA Technical General: DC Electrics Questions
401 exam-style DC Electrics questions for the DGCA Technical Generalpaper (CPL & ATPL). The first 12 are free below with answers and explanations — sign up free to practise all of them with progress tracking.
- Q1
Spare fuses are carried:
- Aat the operators’s discretion.
- Bfor generators only.
- Cby law with a stated minimum number required.
- Dby the first officer.
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Correct answer: C. by law with a stated minimum number required.
This Explanation is Coming Soon
- Q2
How are the loads on an aircraft busbar connected
- A Are in series so that current reduces through the busbar as loads are switched off
- B Are in parallel so that voltage reduces through the busbar as loads are switched off
- C Are in parallel so that current reduces through the busbar as loads are switched off
- D Are in series so that voltage reduces through the busbar as loads are switched off
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Correct answer: C. Are in parallel so that current reduces through the busbar as loads are switched off
All consumers are connected in parallel across the busbar, so each receives full busbar voltage and draws its own current. Switching loads off simply removes their individual current demands, reducing the total current supplied through the busbar while the voltage remains constant.
- Q3
When a battery is nearly discharged, does the
- A Voltage decrease
- B Voltage and current decrease
- C Current increases because voltage has dropped
- D Electrolyte boil
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Correct answer: B. Voltage and current decrease
As a battery approaches full discharge its EMF falls and its internal resistance rises, so the terminal voltage drops and the current it can push through a given load decreases as well. Both voltage and current therefore decrease together.
- Q4
With an almost discharged battery there will be:
- AA decrease of voltage with increasing load
- B Increase of current with decrease of voltage
- C Decrease of current with increasing load
- D Increase of voltage with increasing load
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Correct answer: A. A decrease of voltage with increasing load
A nearly discharged battery has a high internal resistance, so as load current is increased more voltage is dropped internally and the terminal voltage falls markedly. The characteristic sign is therefore decreasing voltage with increasing load.
- Q5
A 12 volt lead acid battery has a broken connection in a cell, the battery:
- A Provides 1/12th less voltage for the same time
- B Provides 1/12th less voltage for 1/12th less time
- C Is unserviceable
- DWill suffer from thermal runaway
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Correct answer: C. Is unserviceable
A broken internal connection in one cell open-circuits the whole series-connected battery, so it can deliver no current at all rather than simply a reduced voltage. The battery is therefore unserviceable and must be replaced.
- Q6
What are the advantages of an earth return system? 1.It is not a single wire system. 2.Short circuits are less likely. 3.Open circuits are less likely. 4.Reduced weight. 5.Easier fault detection and diagnosis.
- A1,2,3,4.
- B2,3,5.
- C3,4.
- DAll of the above.
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Correct answer: C. 3,4.
This Explanation is Coming Soon
- Q7
342.An indication of the battery state of charge or serviceability is
- AThe specific gravity of the electrolyte
- BThe temperature of electrolyte
- CTo check the temperature of electrolyte using a hydrometer
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Correct answer: A. The specific gravity of the electrolyte
The state of charge of a lead-acid battery is indicated by the specific gravity of its electrolyte, measured with a hydrometer: sulphuric acid is consumed as the battery discharges, so the specific gravity falls from about 1.27 fully charged towards 1.17 discharged. Electrolyte temperature is only used to correct the hydrometer reading, not as an indication in itself.
- Q8
428.A non-trip free circuit breaker is:
- Aone which can make a circuit in flight by pushing a button
- Ba wire placed in a conductor which melts under overload
- C an on-off type tumbler switch
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Correct answer: A. one which can make a circuit in flight by pushing a button
In a non-trip-free circuit breaker the contacts follow the push button, so pressing the button in flight can re-make the circuit even while the fault current persists. A trip-free breaker, by contrast, cannot be held closed against a fault because its tripping mechanism is independent of the button.
- Q9
500.Fuses:
- Aprotect the load
- B protect the cable
- C both the cable and load
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Correct answer: C. both the cable and load
A fuse is a deliberately weak link that melts and breaks the circuit when current exceeds its rating, so it protects both the cable and the load: the wiring is saved from overheating and the equipment downstream is disconnected from the fault current.
- Q10
The method of ascertaining the voltage of a standard aircraft lead acid battery is by checking:
- Athe voltage on open dirault
- B the voltage off load
- Cthe voltage with rated load switched ON
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Correct answer: C. the voltage with rated load switched ON
A lead-acid battery's serviceability is checked by reading its voltage with the rated load switched on, because a discharged or defective battery can still show near-normal voltage off load. Only under load does the terminal voltage reveal the battery's true capacity to deliver current.
- Q11
When selecting a fuse for a circuit the governing factor is:
- Athe voltage of the circuit.
- Bthe fuse length and diameter.
- Cthe resistance of the circuit.
- Dthe power requirement of the circuit.
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Correct answer: D. the power requirement of the circuit.
This Explanation is Coming Soon
- Q12
The state of charge of an aircraft battery on an aircraft with a voltmeter would be checked
- A On load
- B Off load
- C With the battery negative terminal disconnected
- D By monitoring the electrolyte resistance
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Correct answer: A. On load
A battery's true state of charge is checked on load, because a healthy battery holds its voltage under a discharge while a weak one sags markedly. An off-load reading can look normal even when the battery cannot deliver current.
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