Fundamentals of Electricity and Electronics Flashcards
What is difference between the conventional current flow theory and electron flow
Conventional current flow theory is a visualization of current as flowing from positive to negative. In actual practice, electrons in a circuit flow from negative to positive (electron theory)
How can you find the polarity of an electromagnet
Hold mangnet in left hand with fingers encircling the coil in the direction electrons flow (neg to pos). Thumb points to North Pole of magnet
What constitutes a capacitor
two conductors separated by an insulator
what is the purpose of a capacitor
it stores electrical energy in electrostatic fields
what is the basic unit of a capacitor
Farad
Why should electrolytic capacitors not be used in an AC circuit
They are polarized. Will accept current of one polarity but block current of another polarity
What is meant by inductance
ability to store electrical energy in electromagnetic field
What is the basic unit inductance
Henry
Give the inductance and the frequency of the AC in a circuit, how do you compute the inductive reactance caused by the coil
XL = 2πfL
Does a capacitor in an AC circuit cause the current to lead or lag the voltage
Lead
Does an inductor in an Ac circuit cause the current to lead or lag the voltage
Lag
What is the basic unit of power in a DC circuit
Watt
What happens to the current in a DC circuit if the voltage is increased but the resistance remains the same
It increases
What are 5 sources of electrical energy
Magnetism
Chemical energy
Light
heat
pressure
Which law of electricity is the most important for an aircraft mechanic to know
Ohms law
What are the elements of ohms law
Voltage (E) (volts)
Current (I)(Amps)
Resistance(R)(ohms)
What is the name of the law that describes the relationship in an electrical circuit of voltage, Current, and resistance
Ohms law
what is the basic equation of ohms law
E=IxR
What is Kirchhoff’s voltage law
states that the algebraic sum of all voltages around a closed path or loop is zero. (sum of all voltage drops equal the total source voltage)
What is the formula for determining power
General power formula= P=I x E
p=power, I=current, e=volts
What is faradays law
law of electromagnetic induction states that the induced EMF or electromagnetic force in a closed loop of wire is proportional to the rate of change of the magnetic flow through a coil of wire
What is Lenz law
That EMF induced in an electric circuit always acts in such a directions that the current it drives around a closed circuit produces a magnetic field, which opposes the change in magnetic field
What is the right hand motor rule
index finger of the right hand is pointed in the direction of the magnetic field and the second finger in the direction of current flow the thumb indicates the direction the current carrying wire moves
What is meant by a Kilowatt
1,000 watts
What is meant by a Megawatt
1,000,000 watts
What instrument is used to measure current flow
Ammeter
What is a megaohm
1 million ohms
What instrument is used to measure electrical resistance
ohmmeter
When measuring resistance of a component with an ohmmeter, should the circuit be energized
no
What instrument is used to measure continuity in an electrical circuit
ohmmeter
in what units is battery capacity expressed
ampere-hours
what instrument is used to measure the specific gravity of the electrolyte in a lead acid battery
Hydrometer
what is voltage
electrical pressure
what is the basic unit of voltage
volt
what instrument is used to measure voltage
voltmeter
to measure voltage, is a voltmeter placed in series or in parallel with source of voltage
parallel
what is the voltage across each resistor connected in parallel across a 12 volt battery
12 volts
what is the open circuit voltage of a lead acid cell
2.1 volts
how is output voltage regulated in a an AC alternator
voltage regulation is accomplished by varying the strength of the AC exciter fields (field voltage)
what is electrical current
the flow of electrons in a circut
what is a basic unit of current flow
the ampere (amp)
what part of an amp is a milliamp
one thousand (0.001) of an amp
what two things happen when current flows through a conductor
heat is generated and a magnetic field surrounds the conductor
to measure current through a component, is an ammeter placed in parallel or in series with the component
in series
what formula is used to find current when voltage and resistance are known
current = voltage divided by resistance
what is meant by resistance in an electrical circuit
the opposition to the flow of electrons
what is the basic unit of electrical resistance
the ohm
what four things affect the resistance of an electrical conductor
the material, the cross-sectional area, the length, and the temperature
how can you tell the resistance of a composition resistor
by a series of colored bands around one end of the resistor
what formula is used to find resistance when voltage and current are known
resistance = voltage divided by current
what is meant by impedance
total opposition to the flow of alternating current. it is the vector sum of resistance, capacitive reactance, and inductive reactance
in what units is impedance measured
ohms
how is resistance calculated in series circut
for resistors in a series configuration, the total resistance of the circut is equal to the sum of the individual resistors
how is resistance calculated in a parallel circut
formula for the total parallel resistance as follows
1/RT = 1/R1 + 1/R2 +
If reciprocal of both sides is taken
RT= 1/ 1/R1+ 1/R2 + 1/R3
what is the total resistance of three 12 ohm resistors connected in series
36 ohms
what is the total resistance of three 12 ohm resistors connected in parallel
4 ohms
what is the formula for power in a DC circut
power= voltage times current
what is the relationship between mechanical and electrical power
1 horsepower= 746 watts
what is meant by true power in an AC circuit
the product of the circuit voltage and the current that is in phase with this voltage
in what unit is true power expressed
in watts
what is meant by apparent power in an ac circut
the product of the circuit voltage and the circuit current, without reference to phase angle
in what units is apparent power expressed
volt-amps
what is meant by reactive power in an AC circut
power consumed in the inductive and capacitive reactances in an AC circuit. Reactive power is also called wattless power
in what units is reactive power expressed
in volt-amps (VAR), kilovolt- amps reactive(KVAR)
what is meant by power factor in an AC circut
ratio of true power to apparent power, it is also the ratio of circut resistance to circut impedence
how many watt of power are consumed by a 1/5 horsepower, 24 volt DC motor that is 75 % efficient
power efficiency is expressed as :
(efficiency= power out/ power in)
power consumed is the same as power in, and 1 horsepower(hp) equals 746 watts:
power in = power out/ efficiency
how much current flows through each of three resistors connected in series if the total current is 3 amps
3 amps
how much current flows through each of three equal resistors connected in parallel if the total current is 3 amps
1 amps
what is meant by the capacity rating of a lead acid battery
the number of hours a battery can supply a given current flow
what electrolyte is used in a lead acid battery
a mixture of sulfuric acid and water
does the specific gravity of the electrolyte In a lead acid battery increase or decrease as the battery becomes discharged
decreases
what is the specific gravity of a fully charged lead acid battery
between 1.275 and 1.300
how many cells are there in a 24 volt lead acid battery
12
what is the range of temperature of the electrolyte in a lead acid battery that does not require a correction when measuring its specific gravity
between 70 and 90 degrees F
how do you treat a lead acid battery compartment to protect it from corrosion
paint it with an asphaltic (tar-base) paint or with a polyurethane enamel
what is used to neutralize spilled electrolyte from a lead acid battery
a solution of bicarbonate of soda and water
how high should the electrolyte level be in s properly serviced lead acid battery
only up to the level of the indicator in the cell
why is the closed circut voltage of a lead acid battery lower than its open circut voltage
voltage is dropped across the internal resistance of the battery
what gasses are released when a lead acid battery is being charged
Hydrogen and oxygen
what is the electrolyte used in a nickel-cadmiun battery
potassium hydroxide and water
why is a hydrometer not used to measure the state of charge of a nickel-cadmuim battery
electrolyte of nickel cadmium battery does not enter into the chemical changes that occur when the battery is charged or discharged. its specific gravity does not change appreciably
is the electrolyte level of nickel cadmium battery lowest when the battery is fully charged or fully discharged
fully discharged
what is a result of cell imbalance in a nickel cadmium battery
low internal resistance allows current to flow between the unbalanced cells and generate heat
what is thermal runaway
large current flow allowed by the low internal resistance causes the cells to produce more heat than they can dissipate. heat further lowers the internal resistance so more current can flow; this continues until the battery destorys itself
how may thermal runaway be prevented
by carefully monitoring the temperature of the cells and controlling the charging current to prevent an excess of current flowing into the battery
how is it possible to know when a nickel-cadmium battery if fully charged
Completely discharge the battery and give it constant current charge to 140% of its ampere-hour capacity
what is used to neutralize spilled electrolyte from a nickel-cadmium battery
solution of boric acid and water
what is a transformer and how does it work
a transformer Is a device that changes electrical energy in an alternating current circut of a given voltage into electrical energy at a different voltage level. it consists of two coils that are not electrically connected but arranged so that the magnetic field surrounding one coil cuts through the other coil
what three things must an electric circut contain
a source of electrical energy, a load to use the energy, and conductors to join the source and the load
what is meant by continuity in an electrical circut
circut is continuous (or complete) when electrons can flow from one terminal of the power source to the other
what is the basic function of a switch
switches control the current flow in most aircraft electrical circuts
what is a relay
a relay is simply an electromechanical switch where a small amount of current can control a large amount of current
what is the function of a current limiter
current limiter is a type of heavy fuse, commonly with rating of 30 amps or greater. they are often used to protect a section of an electrical system, such as a single electrical bus
what materials are fixed resistors made of
most comom fixed resistor are made of a carbon composition. other types of fixed resistor include carbon film, metal-oxide, metal film, and metal glaze. wire-wound resistor are typically used to control large amounts of current and have high power ratings
what are the two main types of variable resistors
rheostat and potentiometer
how can you tell the resistance of a composition resistor
by a series of colored bands around one end of the resistor
what happens to the current in a conductor if the length of the conductor is doubled with all other parameters unchanged
resistance of the conductor would double and current flow would be decreased
explain the basic concept of digital logic, including RAM, ROM, NVRAM, logic gates, inverters, rectifiers and flip flops
what are binary numbers
binary number system has only two digit: 0 and 1. it is also known as a base 2 numbering system
what is electrostatic discharged or (ESD)
is the discharge of static electricity that can build up on a component or a person body. ESD is frequent cause of damage to solid state component and intergrated circut and can be prevented by wearing a grounding wrist strap when handling electrical components
what type of drawing deceits electrical components with respect to each other within a circut
a electrical schematic
what are three types of DC circuits with regards to the placement of the various circut component
series, parallel, series-parallel
what are the two general types of AC motors used in aircraft system
induction motor and synchronous motors
what is the formula used to determine the speed of an AC motor
RPM = (120 x frequency)/number of poles
in what types of applications is a series wound DC motor most often used
applications that require high tourque and low speed, such as a starter motor
what are the two principal parts of a DC motor
field assembly and an armature assembly
