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UKCAA M3 - electrical fundamentals > DC Sources of Electricity > Flashcards

DC Sources of Electricity Flashcards

1
Q

What is a primary cell?

A

What is a primary cell?

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2
Q

Can primary cells be recharged?

A

No, primary cells cannot be recharged and therefore cannot be reused, although they can and should be recycled.

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2
Q

What type of electrolyte is used in nearly all primary cells?

A

Nearly all primary cells use a paste electrolyte, making them dry cells.

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2
Q

Nearly all primary cells use a paste electrolyte, making them dry cells.

A

Zinc-carbon dry cells have a nominal initial voltage of about 1.5 V.

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3
Q

What are the main components of a zinc-carbon dry cell?

A

A zinc-carbon dry cell consists of a zinc container (negative electrode), a carbon rod (positive electrode), and a paste containing manganese (IV) oxide, zinc chloride, ammonium chloride, carbon powder, and water.

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3
Q

What is a disadvantage of zinc-carbon batteries?

A

As the zinc container oxidizes, it can eventually leak, so these batteries should only be installed in devices that are in use and not stored for extended periods.

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3
Q

How do alkaline primary batteries compare to zinc-carbon dry cells?

A

Alkaline batteries can deliver up to five times the energy of similarly-sized zinc-carbon batteries.

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4
Q

What can happen if you try to recharge an alkaline battery that is not designed to be recharged?

A

Attempting to recharge an alkaline battery not designed for recharging can cause the battery to rupture, leading to leakage of the potassium hydroxide electrolyte.

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4
Q

How are aircraft storage batteries composed?

A

Aircraft storage batteries are made of lead acid or nickel-cadmium cells connected in series within the battery case.

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4
Q

What distinguishes secondary cells from primary cells?

A

The electrochemical reactions in secondary (rechargeable) cells are reversible, allowing the chemical reactants to be restored by running a charging current into the cell.

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5
Q

Where are secondary cells commonly used?

A

Secondary cells are used in aircraft, cars, laptops, and many other devices.

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6
Q

How is battery capacity rated?

A

Battery capacity is rated in ampere-hours (Ah). For example, a battery with a capacity of 50 Ah can supply a current of 5 A for 10 hours.

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7
Q

What is the voltage of a fully charged lead acid cell?

A

A fully charged lead acid cell has a voltage of 2.2 V.

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8
Q

What happens during the discharge of a lead acid cell?

A

During discharge, sulfuric acid breaks up into hydrogen and sulfate ions. The sulfate ions combine with the negative lead plate to form lead sulfate, while hydrogen ions combine with the positive plate’s oxygen to form water, creating a flow of electrons from the negative to the positive plate.

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9
Q

What are the main components of a lead acid cell?

A

A lead acid cell consists of positive plates filled with lead peroxide (PbO2), negative plates filled with pure spongy lead (Pb), and an electrolyte made up of 30% sulfuric acid and 70% distilled water.

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10
Q

What happens during the charging of a lead acid cell?

A

During charging, sulfate ions are driven back into the electrolyte, forming sulfuric acid, and the plates return to their original composition of lead peroxide and spongy lead.

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11
Q

What is the voltage of a fully charged nickel cadmium cell?

A

A fully charged nickel cadmium cell has a voltage of 1.2 V.

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12
Q

What are the main components of a nickel cadmium cell?

A

A nickel cadmium cell consists of positive plates impregnated with nickel oxyhydroxide, negative plates made of metallic cadmium, and an electrolyte of potassium hydroxide.

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13
Q

What happens during the discharge of a nickel cadmium cell?

A

During discharge, hydrogen ions from the electrolyte combine with the negative plates, forming cadmium hydroxide, while hydroxide ions from the positive plates move into the electrolyte, creating a flow of electrons from the positive to the negative plate.

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14
Q

When should the electrolyte level of a nickel cadmium battery be checked and refilled?

A

The electrolyte level should be checked and refilled when the battery is fully charged, as the level rises during charging.

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15
Q

What are some advantages of nickel cadmium batteries compared to lead acid batteries?

A

Advantages of nickel cadmium batteries include higher discharge current tolerance, constant closed circuit voltage during discharge, higher energy density, and a greater number of charge/discharge cycles.

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16
Q

What are some disadvantages of nickel cadmium batteries compared to lead acid batteries?

A

Disadvantages of nickel cadmium batteries include higher cost, more complicated charging requirements, risk of thermal runaway, and high toxicity of cadmium.

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17
Q

What are the common types of primary coin cells and their uses?

A

Common types of primary coin cells include mercury oxide cells (used in hearing aids, watches, meters, and cameras), silver oxide cells (used in watches, calculators, and hearing aids), and lithium coin cells (used in pacemakers, cameras, and video cameras).

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18
Q

What are the key characteristics of mercury oxide coin cells?

A

Mercury oxide coin cells have a rated voltage of 1.35 V, constant internal resistance during discharge, and constant voltage even under continuous operation.

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19
Q

What are the key characteristics of silver oxide coin cells?

A

Silver oxide coin cells have a rated voltage of 1.55 V, high energy density, and low voltage depression.

20
Q

What are the key characteristics of lithium coin cells?

A

Lithium coin cells have high-rated voltages of up to 3.5 V, high energy density, and long lifespan.

21
Q

In what form were sealed nickel cadmium batteries developed for portable electronic devices?

A

Sealed nickel cadmium batteries were developed in the form of round or coin cells for portable electronic devices.

22
Q

Why don’t sealed nickel cadmium batteries change their electrolyte during charging?

A

The gases generated during the charging process are bound again, so the electrolyte does not change.

23
Q

How can batteries be configured in terms of cell connections?

A

Batteries can comprise a single cell, cells connected in series, cells connected in parallel, or cells connected in both series and parallel.

24
Q

What creates a series connection in power sources?

A

Connecting unlike terminals of power sources creates a series connection. pos + to neg -

25
Q

How does the total voltage of cells connected in series compare to the voltage of individual cells?

A

The total voltage is the sum of the voltages of the individual cells when connected in series.

26
Q

What happens to the voltage when cells are connected in series?

A

The voltage increases.

27
Q

What is constant in a series circuit with cells?

A

The current is constant; the same current flows through each cell.

28
Q

How does connecting cells in series affect the internal resistance of the battery?

A

The internal resistance of the battery is equal to the sum of the internal resistance of the cells, increasing the total internal resistance.

29
Q

What happens to the terminal voltage of a battery when connected to an external load?

A

The terminal voltage drops due to the internal resistance of the battery.

30
Q

How is a parallel connection created in power sources?

A

Connecting like terminals of power sources to each other creates a parallel connection. Pos + to Pos+

31
Q

What effect does connecting cells in parallel have on voltage and internal resistance?

A

Connecting cells in parallel provides the same voltage but lowers the total internal resistance.

32
Q

How does a battery with cells in parallel benefit in terms of current supply?

A

It can supply a larger current.

32
Q

Why does a parallel connection of cells lower the total internal resistance?

A

Because connecting resistors in parallel lowers the total resistance.

33
Q

What happens to the current through each power source when cells are connected in parallel with series switches, and both switches are closed?

A

A current of only 1 A flows through each of the two power sources.

34
Q

What is the total current and voltage for two power sources connected in parallel with series switches?

A

The total current is 2 A, and the total voltage is 20 V.

35
Q

How is the total current in a parallel connection of power sources determined?

A

The total current is the sum of the individual currents.

36
Q

How does the total resistance in a parallel connection compare to the individual resistances?

A

The total resistance is lower than the lowest individual resistance.

37
Q

What remains constant across parallel branches in a parallel connection of cells?

A

The voltage remains constant across parallel branches.

38
Q

When is a parallel connection of power sources applied?

A

A parallel connection is applied if the required current exceeds the permitted load of a single power source (to prevent overload).

39
Q

Why are generators in power plants connected in parallel?

A

To meet high current demands that exceed the capacity of a single generator.

40
Q

Formula for terminal voltage of a battery

A

Vt = EMF - Ri

41
Q

What happens to metals when heat is applied?

A

Applying heat to metals increases their temperature, the vibration of the atoms in the metal lattice, and the proper motion of the electrons.

42
Q

How do electrons in a heated metal behave?

A

Electrons in a heated metal behave like particles in a gas, moving faster and faster when heated.

43
Q

Why do different metals have different electron densities?

A

Different metals have different numbers of free electrons, leading to different electron densities.

44
Q

What occurs when metals with different electron densities touch each other?

A

Electrons move from the region of higher electron density to the region of lower electron density, and this effect is greater at higher temperatures.

45
Q

What is generated when two different metals are connected at one end and heated?

A

A voltage, referred to as “thermoelectric voltage”, is generated between the two free ends.

46
Q

What is a thermocouple?

A

A thermocouple is a power supply created by heating the junction of two different metals, generating thermoelectric voltage.

47
Q

On what factors does the thermoelectric voltage depend?

A

The thermoelectric voltage depends on the temperature difference between the junction and the two free ends, as well as the combination of metals.

48
Q

What is the thermoelectric voltage for a Chromel-Alumel combination per 100 °C?

A

The thermoelectric voltage for a Chromel-Alumel combination is 4.2 mV per 100 °C.

49
Q

What is the thermoelectric voltage for a Bismuth-Antimony combination per 100 °C?

A

The thermoelectric voltage for a Bismuth-Antimony combination is 10.0 mV per 100 °C.

50
Q

Q: What is the thermoelectric voltage for a Constantan-Copper combination per 100 °C?

A

The thermoelectric voltage for a Constantan-Copper combination is 4.2 mV per 100 °C.

51
Q

What is the thermoelectric voltage for a Platinum-Platinum Rhodium combination per 100 °C?

A

A: The thermoelectric voltage for a Platinum-Platinum Rhodium combination is 1.0 mV per 100 °C.

52
Q

In what temperature range are thermocouples used to measure temperatures?

A

Thermocouples are used to measure temperatures ranging from -200 °C to 2300 °C.

53
Q

Where are thermocouples commonly used for temperature measurement?

A

Thermocouples are used for remote measurements or in hard-to-reach places, such as ovens and windings.

54
Q

How are thermocouples used in aviation?

A

In aviation, thermocouples are mainly used to measure exhaust gas temperatures of engines.

55
Q

Which alloys are used in thermocouples for modern aircraft engines?

A

The alloys chromel and alumel are used in thermocouples for modern aircraft engines.

UKCAA M3 - electrical fundamentals (11 decks)

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