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151/23/005 > Electrical principles > Flashcards

Electrical principles Flashcards

1
Q

definition of DC

A

current that flows in one direction only

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2
Q

definition of AC

A

is current that periodically changes direction

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3
Q

definition of electric current

A

is rate of movement of charge measured in amperes

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4
Q

definition of EMF

A

is force that causes current to flow measured in volts

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5
Q

definition of potential difference

A

the change in electrical potential between two points in a circuit

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6
Q

definition of resistance

A

is the opposition to current flow that a resistor exerts in a circuit

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7
Q

definition of absolute potential

A

is the voltage at a point in a circuit with reference to earth

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8
Q

definition of a conductor

A

is a material with low resistance that allows current flow

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9
Q

definition of an insulator

A

is a material with high resistance that dose not allow current to flow

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10
Q

definition of a semiconductor

A

is a material that is neither a good conductor or insulator but can be made to exhibit some great properties

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11
Q

definition of an ammeter

A

is an instrument that has low resistance and is used to measure current. it is placed in series with the load

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12
Q

definition of a voltmeter

A

is an instrument that is used to measure power

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13
Q

definition of ohmmeter

A

is an instrument that is used to measure resistance. is is placed in parallel with the resistor after is has been removed from the circuit

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14
Q

definition of a wattmeter

A

is an instrument that is used to measure power

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15
Q

definition of mit420 or bridge megger

A

are instruments that are used to measure both continuity and insulation resistance

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16
Q

definition of tachometer or stroboscope

A

is an instrument that is used to measure rotational speed

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17
Q

definition of ohms law

A

the current flowing in a circuit is directly proportional to the voltage applied inversely proportional to the resistance as long as the temp remains constant

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18
Q

factors that effect resistance

A
  • type of material
  • length
  • cross sectional area
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19
Q

what are kirchoffs laws

A

current law
voltage law

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20
Q

define kirchoffs current law

A

the amount of current flowing towards a junction or node in a circuit is equal to the amount flowing away

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21
Q

define kirchoffs voltage law

A

the sum of the voltage drops around a closed loop in a circuit is equal to the EMFs acting in a closed loop

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22
Q

definition of a potentiometer

A

uses three terminals and is used for voltage control

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23
Q

definition of a rheostat

A

uses two terminals and is used for current control

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24
Q

definition of a capacitor

A

is a deceive that is used to temporally store electrical energy or charge. two plates that are separated by a dielectric

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25
factors that effect capacitance
- number of turns of wire - the cross sectional area of the coil - the presence of a magnetic core - the way the turns are arranged
26
definition of time constant
it is the time current would take to reach its maximum if it continued to raised at its initial rate
27
explain how an ac generator works
when a conductor is passed through a magnetic field an EMF is induced into it. in a ac generator coils of wire are turned in a magnetic field by a prime mover. As the coils cut the flux an ac EMF is induced which is transmitted to the load via slip rings and brushes
28
definition of periodic time
is the time for one cycle of an ac waveform
29
definition of RMS value
is the value of the ac waveform that would give the same heating effect as the equivalent
30
definition of frequency
is the number of complete ac cycles each second. measured in Hertz
31
explain how a transformer works
- an ac voltage is connected to the primary coils which causes an ac current to flow in the coils - the ac current sets up alternating flux in the core - the flux in the core cuts the secondary coils and induces an ac EMF in them by mutual inductance - when the secondary coils are connected to a load an ac current will flow which creates a ac voltage across the load
32
definition of power rating
this is the maximum apparent power the transformer can transform without overheating
33
what are the types of transformer cores
shell and core
34
what are the three effects of electric current
- magnetic current - heating current - chemical current
35
what are the practical applications of electrical current - magnetic effect
- bells - relays - motors - generators - transformers - telephones
36
what are the practical applications of electrical current - heating effect
- cookers - water heaters - electric fires - irons - furnaces
37
what are the practical applications of electrical current - chemical effect
- primary and secondary cells - electroplating
38
how do you calculate voltage distribution
Vin = (R2/R1+R2) Vin
39
definition of resistance
is the opposition to current flow that a resistor
40
definition of inductive reactance
is the opposition to current flow that an inductor exters in an ac circuit
41
definition of capacitive reactance
is the opposition to current flow that a capacitor exerts in an ac circuit
42
definition of impedance
is the total opposition to current flow that is exerted by the combined components in an ac circuit
43
discribe magnets
- like poles repel - unlike poles attract
44
definition of magneto motive force (mmf)
the force that causes a magnetic field to be set up around a magnetic circuit. measured in Amperes (A)
45
definition of magnetic flux
is the amount of magnetic field created by a magnetic source. measured in Weber
46
definition of magnetic feild
the area around a bar magnet where the magnetic force can be detected
47
definition of magnetic flux density
is the amount of magnetic flux passing through a defined area. measured in tesla
48
definition of magnetic field strength
is the amount of mmf per unit length of a magnetic circuit
49
explain motor effect
when current carrying conductor is placed in a magnetic field is experiences a force. the direction of the force can be determined by using Flemings left hand rule
50
explain how a motor works
when a current carrying conductor is placed in a magnetic field is experiences a force. in a motor are loops of wire in a magnetic field when current flows through the loops they experience forces that cause the loop to rotate creating torque
51
what s faradays laws of electromagnetic induction
whenever a conductor is passed through or field cuts a conductor an EMF will be induced into it. the size of the EMF depends on the rate of cutting the flux
52
explain lenz law
the result will always cause an effect that will oppose the production of the result
53
how dose a dc generator work
when a conductor is passed through a magnetic field, emf is induced coils of wire are turned in a magnetic field by a prime mover as the coils cut out the flux an ac emf is induced which transmited to the load via a commutator and brushes the commutator converts the ac to dc
54
definition of self inductance
is when an emf is induced into a coil caused by the current changing in it
55
definition of mutual inductance
is when an emf is induced into a coil by the current changing in an adjacent coil
56
factors that effect inductance
- number if turns of wire - the cross sectional area of the coil - the presences of a magnetic core - the way the turns are arranged
57
what are the types of semi conductors
silicon and germanium
58
what are the types of reistors and there uses
surface mount technology - elecronic equipment wire wound resistors - power circuits and motor starters metal oxide resistors - electronic equipment carbon resistors - electronic equipment
59
how do you identify the value of resistors
4/5 band letter and digit
60
how to calculate Ct of capcitors in series
c= product / sum
61
how do u=you used flemings left hand rule
first finger- feild second finger- current thumb - motion
61
how do you calculate av value of a sine wave
av value = 0.637 x maximum valve
61
how do you calculate rms value of a sine wave
rms= 0.707 x maximum value
61
how do you flemings right hand rule
first finger - field thumb- motion second finger - EMF

151/23/005 (13 decks)

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