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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
Q

factors that effect capacitance

A
  • number of turns of wire
  • the cross sectional area of the coil
  • the presence of a magnetic core
  • the way the turns are arranged
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26
Q

definition of time constant

A

it is the time current would take to reach its maximum if it continued to raised at its initial rate

27
Q

explain how an ac generator works

A

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
Q

definition of periodic time

A

is the time for one cycle of an ac waveform

29
Q

definition of RMS value

A

is the value of the ac waveform that would give the same heating effect as the equivalent

30
Q

definition of frequency

A

is the number of complete ac cycles each second. measured in Hertz

31
Q

explain how a transformer works

A
  • 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
Q

definition of power rating

A

this is the maximum apparent power the transformer can transform without overheating

33
Q

what are the types of transformer cores

A

shell and core

34
Q

what are the three effects of electric current

A
  • magnetic current
  • heating current
  • chemical current
35
Q

what are the practical applications of electrical current
- magnetic effect

A
  • bells
  • relays
  • motors
  • generators
  • transformers
  • telephones
36
Q

what are the practical applications of electrical current
- heating effect

A
  • cookers
  • water heaters
  • electric fires
  • irons
  • furnaces
37
Q

what are the practical applications of electrical current
- chemical effect

A
  • primary and secondary cells
  • electroplating
38
Q

how do you calculate voltage distribution

A

Vin = (R2/R1+R2) Vin

39
Q

definition of resistance

A

is the opposition to current flow that a resistor

40
Q

definition of inductive reactance

A

is the opposition to current flow that an inductor exters in an ac circuit

41
Q

definition of capacitive reactance

A

is the opposition to current flow that a capacitor exerts in an ac circuit

42
Q

definition of impedance

A

is the total opposition to current flow that is exerted by the combined components in an ac circuit

43
Q

discribe magnets

A
  • like poles repel
  • unlike poles attract
44
Q

definition of magneto motive force (mmf)

A

the force that causes a magnetic field to be set up around a magnetic circuit. measured in Amperes (A)

45
Q

definition of magnetic flux

A

is the amount of magnetic field created by a magnetic source. measured in Weber

46
Q

definition of magnetic feild

A

the area around a bar magnet where the magnetic force can be detected

47
Q

definition of magnetic flux density

A

is the amount of magnetic flux passing through a defined area. measured in tesla

48
Q

definition of magnetic field strength

A

is the amount of mmf per unit length of a magnetic circuit

49
Q

explain motor effect

A

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
Q

explain how a motor works

A

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
Q

what s faradays laws of electromagnetic induction

A

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
Q

explain lenz law

A

the result will always cause an effect that will oppose the production of the result

53
Q

how dose a dc generator work

A

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
Q

definition of self inductance

A

is when an emf is induced into a coil caused by the current changing in it

55
Q

definition of mutual inductance

A

is when an emf is induced into a coil by the current changing in an adjacent coil

56
Q

factors that effect inductance

A
  • 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
Q

what are the types of semi conductors

A

silicon and germanium

58
Q

what are the types of reistors and there uses

A

surface mount technology - elecronic equipment
wire wound resistors - power circuits and motor starters
metal oxide resistors - electronic equipment
carbon resistors - electronic equipment

59
Q

how do you identify the value of resistors

A

4/5 band
letter and digit

60
Q

how to calculate Ct of capcitors in series

A

c= product / sum

61
Q

how do u=you used flemings left hand rule

A

first finger- feild
second finger- current
thumb - motion

61
Q

how do you calculate av value of a sine wave

A

av value = 0.637 x maximum valve

61
Q

how do you calculate rms value of a sine wave

A

rms= 0.707 x maximum value

61
Q

how do you flemings right hand rule

A

first finger - field
thumb- motion
second finger - EMF

151/23/005 (13 decks)

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