3.4 - Generation of Electricity - 4q

Question 1

Discuss the method od producing electromotive force (EMF) through:

Friction

Answer 1

Also; Static Electricity

Voltage produced by rubbing two materials together

Question 2

Discuss the method od producing electromotive force (EMF) through:

Pressure

Answer 2

(Piezo Electricity)

Voltage produced by squeezig crystals of certain substances

Question 3

Discuss the method od producing electromotive force (EMF) through:

Heat

Answer 3

(Thermo Electricity)

Voltage produced by heating the joint where two dissimilar metals are joined

Question 4

Discuss the method od producing electromotive force (EMF) through:

Light

Answer 4

(Photo Electricity)

Voltage produced by light striking photosenitive substances

Question 5

Discuss the method od producing electromotive force (EMF) through:

Chemical Action

Answer 5

(Chemo Electricity)

Voltage produced by chemical reaction in a battery cell

Question 6

Discuss the method od producing electromotive force (EMF) through:

Magnetism

Answer 6

(Electromagnetism)

Voltage produced in a conductor when the conductor moves through a magnetic field, or a magnetic field moves through the conductor in such a manner as to cut the magnetic lines of force of the field.

Question 7

Static electricity is a _____ ____ to modern electronic circuits and special handling precautions must be observed when handling such equipment.

Answer 7

serious hazard

Question 8

Another word for producing voltage by pressure and secribe how it occurs.

Answer 8

Voltage produced by pressure is referred to as piezoelectricity. It is produced by compressing or decompressing crystals of certain substances. To study this form of electricity, the meaning of the word ‘‘crystal’’ must first be understood. In a crystal, the molecules are arranged in an orderly and uniform manner.

Question 9

Describe the Thompson Effect

Answer 9

This effect describes the tendency for electrons to migrate across regions of different temperature in a metal bar. SINGLE METAL BAR

Copper heated at one end, electrons flow away from heated end.

Iron heated at one end, electrons flow towards the hot end.

Question 10

Describe The Seebeck Effect

Answer 10

This effect occurs when two dissimlar metals are joined end to end to form two junctions, and one of the junctions is made hotter than the other. A current can be observed to flow around the circuit.

TWO DISSIMILAR METAL BARS

Question 11

In terms of the Seebeck Effect, The current flowing can be found to be _______ to the difference in ______ between the hot junction and the cold junction, and is also dependent on the two _____ used.

Answer 11

proportional

Temperature

Metals

Question 12

Which has a greater power capacity:

Crystals or Thermocouples

Answer 12

Thermocouples have somewhat greater power capacities than crystals, but their capacity is still very small if compared to some other sources.

Question 13

What does the thermoeletric voltage in a thermocouple depend mainly on?

What are they used for?

Answer 13

The thermoelectric voltage in a thermocouple depends mainly on the difference in temperature between the hot and cold junctions.

They are widely used to measure temperature and as heat sensing devices in automatic temperature control equipment.

Question 14

Why would thermocouples be used over traditional thermometers?

Answer 14

Thermocouples generally can by subject to much greater temperatures than ordinary thermometers, such as the mercury and alcohol types.

Question 15

Thermocouples are used on aircraft to measure exhaust gas temperature and cylinder head temperature.

What are the most popular thermocouple metal combinations used on aircraft?

(VARIOUS METALS CAN BE USED AS THERMOCOUPLES)

Answer 15

Exhaust Gas Temperature - Chromel and Alumel

Cylinder Head Temperature - Copper and Constantan

Question 16

When light strikes the surface of a substance, it may dislodge electrons from their orbits around the surface atoms of the substance. This occurs because light has _____

Answer 16

Energy

Question 17

What are the photosensitive materials most commonly used to produce photoelectric voltage?

Answer 17

The photosensitive materials most commonly used to produce a photoelectric voltage are various compounds of

silver oxide, copper oxide, silicon

Question 18

The substance between two electrodes allowing current flow is called ?

Answer 18

This solution is called the electrolyte.

Question 19

Because current flow is always in the same direction, the current flow is called direct current or dc and the EMF supplied by the battery is referred to as ….

Answer 19

dc voltage or volts dc

Question 20

The most widely used method of producing electrical power including over 99 percent of all electrical power available is produced by ….

Answer 20

Magnetism

Question 21

What is magneto-electricity?

Answer 21

When a conductor is moved through a magnetic field, an EMF is produced.

This is called magneto-electricity

Question 22

If a conductor forms a closed loop acroos a potential difference in a magnet, what will happen?

Answer 22

If the conductor forms a closed loop, then the electrons will flow through the conductor. If the conductor does not form a closed loop, a potential difference is still present.

Question 23

What 3 factors does the induced EMF in magnetism depend on?

Answer 23

The value of an induced EMF depends on three factors (Magnetism)

• The Strength of the magnetic field
• The speed of rotation
• The number of wires moving through the magnetic field

Question 24

Briefly describe Thermal Runaway (Overcharge Runaway)

Answer 24

occurs Latter part of charge cycle

NI/Cd most prone - as battery reaches charged state.

Higher gassing takes place - temperature rises - internal resistance falls and voltage fall

Internal resistance falls further - more current - higher temp …

Cycle eventually fire

Question 25

What are some battery cells that my be used in Emergency Lighting Batteries on a/c

Answer 25

Dry Cell (Carbon/ Zinc ) - Primary

Ni/Cd cell (secondary)

Question 26

How do you charge a battery?

Answer 26

Connect in parallel

Positive (red lead) to red terminal

Negative (black lead) to black terminal

Question 27

What is the difference between Constant Voltage Charging and Pulse Charging?

Answer 27

In Constant Voltage Charging - The battery is quickly charged but the cells can be unbalanced.

In Pulse Charging - Done to latter 10% after constant voltage charging - pulses help to elinate cell imbalances.

Question 28

Formula for Ampere Hour Capacity:

Answer 28

Discharge Current (AMPS) x Discharge Time (Hours) = AH

Question 29

Answer 29

Question 30

Nickel Cadmium batteries have a memory effect and need to be restored through Deep cycling.

How can a Ni/Cd cell that has its capacity reduced by repeated shallow charges be restored to its full capacity?

Answer 30

Completely discharge the cell and then overcharge to 140% of its rated Ampere-Hour Capacity.

Question 31

What does AAA stand for?

Answer 31

Always Add Acid

to water

Question 32

What is the purpose of a hydrometer in a cell?

Answer 32

To measure relative density / specific gravity of the electrolyte

Has no units as is a ratio

Question 33

Discuss

Answer 33

(c)

Question 34

What can a Thermohydrometer do?

Answer 34

Hydrometer(measure RD/SG) enclosing a thermometer (MeASURE temp)

Question 35

What would you use to test the temperature of an electrolyte?

Answer 35

To obtain the temperature of the electrolyte, a mercury glass thermometer calibrated to a suitable scale.

Glass is vital, thermocouples and other will not work as will react with electrolyte as is metal

Question 36

What is the sign of an electrolyte spillage?

Answer 36

The top of cells will take the form of a white crystal powder.