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Module 3 - Electrical Fundamentals > DC SOURCES OF ELECTRICITY > Flashcards

DC SOURCES OF ELECTRICITY Flashcards

1
Q

What is a primary cell?

A

Primary cells can immediately supply voltage without charging beforehand. The electrochemical processes taking place are not reversible.

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2
Q

Galvanic cells can only? …

A

Galvanic cells can only supply a certain current, i.e., a certain charge, over a certain period of time.

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3
Q

Primary cells are typically?

A

Dry cells.

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4
Q

What is a dry cell?

A

These are a type of galvanic cell in which the electrolyte is a paste rather than a liquid.

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5
Q

What is the initial voltage of zinc carbon dry cells?

A

1.5V

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6
Q

What is the disadvantage of zinc carbon dry cells?

A

One disadvantage of these batteries is that as the zinc container oxidizes, its contents can eventually leak.

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7
Q

What is the advantage of alkaline batteries?

A

An alkaline can deliver up to five times the energy of a similarly-sized, zinc-carbon battery.

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8
Q

Do alkaline batteries have the same issue as zinc carbon dry cells?

A

Yes

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9
Q

What is it that alkaline batteries leak?

A

Potassium hydroxide

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10
Q

A secondary cell can be?

A

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

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11
Q

In aircraft batteries the cells are connected in?

A

Series

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12
Q

What is the voltage of a lead acid cell?

A

2.2V

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13
Q

What is the discharge voltage of a lead acid cell?

A

1.83 V

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14
Q

What is the voltage of a Nickel cadmium cell?

A

1.2V

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15
Q

What is the Discharge voltage of a Nickel cadmium cell?

A

1.0V

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16
Q

When is the electrolyte level lowest in a Nickel cadmium cell?

A

When fully discharged

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17
Q

What is the voltage of Mercury Oxide Coin Cells?

A

1.35V

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18
Q

What is the voltage of Silver Oxide Coin Cells?

A

1.55V

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19
Q

What is the voltage of Lithium Coin Cells?

A

3.5V

20
Q

How do you create a series connection in batteries?

A

Connecting unlike terminals of power sources creates a series connection.

21
Q

With batteries what does connecting them in series do to the voltage?

A

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

22
Q

With battery connected in series, what happens to the available current?

A

The current through a series circuit is constant, i.e., the same current flows through each cell.

23
Q

With cells connected in series what happens to the internal resistance of the battery?

A

When the cells within a battery are connected in series, the internal resistance of the battery is equal to the sum of the internal resistance of the cells. Therefore, a series connection increases the total internal resistance.

24
Q

How do you create a parallel coonection?

A

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

25
Q

What happens to the voltage if power sources are connected in parallel?

A

Connecting like power sources in parallel provides the same voltage but lowers the total internal resistance of the supply, because connecting resistors in parallel lowers the total resistance.

26
Q

A battery with cells in parallel can supply more or less current than a battery in series?

A

More

27
Q

What is terminal voltage?

A

Due to the internal resistance of the power source, the total source voltage is not available at the terminals, only the so-called “terminal voltage” is.

28
Q

What causes the internal resistance in a battery?

A

In batteries, it is mainly due to the resistance of the electrolyte and the plates.

29
Q

What causes the internal resistance in generators?

A

In electrical generators, it is mainly the resistance of the machine windings.w

30
Q

What happens to terminal voltage as current is drawn?

A

As the current drawn from the supply increases the terminal voltage falls.

31
Q

The fall in terminal voltage is? …

A

Assuming that the internal resistance remains constant, the fall in terminal voltage is directly proportional to the load current.

32
Q

What happens to current and voltage in a generator operating of load?

A

No current flows and, therefore, the terminal voltage (VT) is the same as the source voltage (Vo)

33
Q

What limits current flow in a short circuit condition?

A

The short circuit current is only limited by the internal resistance of the battery.

34
Q

What can be said about a batteries internal resistance as it is discharging?

A

A battery’s internal resistance always becomes greater as the battery discharges.

35
Q

What is the thermoelectric voltage of Chromel – Alumel

A

4.2 mV per 100 °C

36
Q

What is the thermoelectric voltage of Bismuth – Antimony

A

10.0 mV per 100 °C

37
Q

What is the thermoelectric voltage of Constantan – Copper

A

4.2 mV per 100 °C

38
Q

What is the thermoelectric voltage of Platinum – Platinum Rhodium

A

1.0 mV per 100 °C

39
Q

What temp range are thermocouples used for?

A

ranging from -200 °C to 2300 °C

40
Q

What materials are used in modern thermocouples?

A

The alloys chromel and alumel are used in modern engines.

41
Q

How does a photo cell work?

A

Exposure to light releases electrons from the semiconductor layer, which then flow to the metal skin. The base plate is therefore positively charged, and the metal skin negatively charged, thereby generating a voltage.

42
Q

What does the voltage created depend on in a photo cell?

A

The voltage depends on the light intensity, the type of light, and the depletion layer type.

43
Q

Explain the construction of a photo cell?

A

A depletion layer photo-cell (photovoltaic or PV cell) consists of a metallic base plate, with good conductivity, attached to a semiconductor layer. A thin translucent metal skin is vaporised onto this layer as a counter electrode.

44
Q

What materials are commonly used in photo cells?

A

Silicon and selenium PV cells are common.

45
Q

What output can you expect from a photo cell?

A

Solar cells can produce a voltage of approximately 0.6 V and a power of approximately 10 mW per cm2 of active area.

Module 3 - Electrical Fundamentals (17 decks)

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