DC SOURCES OF ELECTRICITY

Question 1

What is a primary cell?

Answer 1

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

Question 2

Galvanic cells can only? …

Answer 2

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

Question 3

Primary cells are typically?

Answer 3

Dry cells.

Question 4

What is a dry cell?

Answer 4

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

Question 5

What is the initial voltage of zinc carbon dry cells?

Answer 5

1.5V

Question 6

What is the disadvantage of zinc carbon dry cells?

Answer 6

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

Question 7

What is the advantage of alkaline batteries?

Answer 7

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

Question 8

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

Answer 8

Yes

Question 9

What is it that alkaline batteries leak?

Answer 9

Potassium hydroxide

Question 10

A secondary cell can be?

Answer 10

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.

Question 11

In aircraft batteries the cells are connected in?

Answer 11

Series

Question 12

What is the voltage of a lead acid cell?

Answer 12

2.2V

Question 13

What is the discharge voltage of a lead acid cell?

Answer 13

1.83 V

Question 14

What is the voltage of a Nickel cadmium cell?

Answer 14

1.2V

Question 15

What is the Discharge voltage of a Nickel cadmium cell?

Answer 15

1.0V

Question 16

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

Answer 16

When fully discharged

Question 17

What is the voltage of Mercury Oxide Coin Cells?

Answer 17

1.35V

Question 18

What is the voltage of Silver Oxide Coin Cells?

Answer 18

1.55V

Question 19

What is the voltage of Lithium Coin Cells?

Answer 19

3.5V

Question 20

How do you create a series connection in batteries?

Answer 20

Connecting unlike terminals of power sources creates a series connection.

Question 21

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

Answer 21

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

Question 22

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

Answer 22

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

Question 23

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

Answer 23

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.

Question 24

How do you create a parallel coonection?

Answer 24

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

Question 25

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

Answer 25

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.

Question 26

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

Answer 26

More

Question 27

What is terminal voltage?

Answer 27

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.

Question 28

What causes the internal resistance in a battery?

Answer 28

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

Question 29

What causes the internal resistance in generators?

Answer 29

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

Question 30

What happens to terminal voltage as current is drawn?

Answer 30

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

Question 31

The fall in terminal voltage is? ...

Answer 31

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

Question 32

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

Answer 32

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

Question 33

What limits current flow in a short circuit condition?

Answer 33

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

Question 34

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

Answer 34

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

Question 35

What is the thermoelectric voltage of Chromel – Alumel

Answer 35

4.2 mV per 100 °C

Question 36

What is the thermoelectric voltage of Bismuth – Antimony

Answer 36

10.0 mV per 100 °C

Question 37

What is the thermoelectric voltage of Constantan – Copper

Answer 37

4.2 mV per 100 °C

Question 38

What is the thermoelectric voltage of Platinum – Platinum Rhodium

Answer 38

1.0 mV per 100 °C

Question 39

What temp range are thermocouples used for?

Answer 39

ranging from -200 °C to 2300 °C

Question 40

What materials are used in modern thermocouples?

Answer 40

The alloys chromel and alumel are used in modern engines.

Question 41

How does a photo cell work?

Answer 41

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.

Question 42

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

Answer 42

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

Question 43

Explain the construction of a photo cell?

Answer 43

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.

Question 44

What materials are commonly used in photo cells?

Answer 44

Silicon and selenium PV cells are common.

Question 45

What output can you expect from a photo cell?

Answer 45

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