3.4 - Generation of Electricity - 4q Flashcards
Discuss the method od producing electromotive force (EMF) through:
Friction
Also; Static Electricity
Voltage produced by rubbing two materials together
Discuss the method od producing electromotive force (EMF) through:
Pressure
(Piezo Electricity)
Voltage produced by squeezig crystals of certain substances
Discuss the method od producing electromotive force (EMF) through:
Heat
(Thermo Electricity)
Voltage produced by heating the joint where two dissimilar metals are joined
Discuss the method od producing electromotive force (EMF) through:
Light
(Photo Electricity)
Voltage produced by light striking photosenitive substances
Discuss the method od producing electromotive force (EMF) through:
Chemical Action
(Chemo Electricity)
Voltage produced by chemical reaction in a battery cell
Discuss the method od producing electromotive force (EMF) through:
Magnetism
(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.
Static electricity is a _____ ____ to modern electronic circuits and special handling precautions must be observed when handling such equipment.
serious hazard
Another word for producing voltage by pressure and secribe how it occurs.
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.
Describe the Thompson Effect
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.
Describe The Seebeck Effect
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
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.
proportional
Temperature
Metals
Which has a greater power capacity:
Crystals or Thermocouples
Thermocouples have somewhat greater power capacities than crystals, but their capacity is still very small if compared to some other sources.
What does the thermoeletric voltage in a thermocouple depend mainly on?
What are they used for?
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.
Why would thermocouples be used over traditional thermometers?
Thermocouples generally can by subject to much greater temperatures than ordinary thermometers, such as the mercury and alcohol types.
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)
Exhaust Gas Temperature - Chromel and Alumel
Cylinder Head Temperature - Copper and Constantan
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 _____
Energy
What are the photosensitive materials most commonly used to produce photoelectric voltage?
The photosensitive materials most commonly used to produce a photoelectric voltage are various compounds of
silver oxide, copper oxide, silicon
The substance between two electrodes allowing current flow is called ?
This solution is called the electrolyte.
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 ….
dc voltage or volts dc
The most widely used method of producing electrical power including over 99 percent of all electrical power available is produced by ….
Magnetism
What is magneto-electricity?
When a conductor is moved through a magnetic field, an EMF is produced.
This is called magneto-electricity
If a conductor forms a closed loop acroos a potential difference in a magnet, what will happen?
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.
What 3 factors does the induced EMF in magnetism depend on?
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
Briefly describe Thermal Runaway (Overcharge Runaway)
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
What are some battery cells that my be used in Emergency Lighting Batteries on a/c
Dry Cell (Carbon/ Zinc ) - Primary
Ni/Cd cell (secondary)
How do you charge a battery?
Connect in parallel
Positive (red lead) to red terminal
Negative (black lead) to black terminal
What is the difference between Constant Voltage Charging and Pulse Charging?
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.
Formula for Ampere Hour Capacity:
Discharge Current (AMPS) x Discharge Time (Hours) = AH
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?
Completely discharge the cell and then overcharge to 140% of its rated Ampere-Hour Capacity.
What does AAA stand for?
Always Add Acid
to water
What is the purpose of a hydrometer in a cell?
To measure relative density / specific gravity of the electrolyte
Has no units as is a ratio
Discuss
(c)
What can a Thermohydrometer do?
Hydrometer(measure RD/SG) enclosing a thermometer (MeASURE temp)
What would you use to test the temperature of an electrolyte?
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
What is the sign of an electrolyte spillage?
The top of cells will take the form of a white crystal powder.
