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Electrical Science Exam > Exam Prep > Flashcards

Exam Prep Flashcards

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1
Q

Luminous efficacy equation

A
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2
Q

Illuminance (E)=
Density

A

The density of luminous flux reaching a surface LUX

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3
Q

Luminous flux (F)=
Total

A

The total power of a light source in a particular direction measured in candelas (cd)

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4
Q
A

Split phase motor
A) main
B) rotor
C) start windings
D) Centrifugal switch

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5
Q
A

Capacitor start induction motor
A) Main windings
B) Rotor
C) Start windings
D) Capacitor
E) Centrifugal switch

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6
Q

Stop buttons on motors are always wired in

A

Series with each other

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7
Q

Start buttons are always wired in

A

Parallel with each other

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8
Q

What are the three main types of motor overload unit

A

Thermal
Magnetic
Electronic

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9
Q

Turns ratio are always written down with the number of primary turns first so if a transformer had 260 primary turns and 130 secondary turns the ratio would be written out like…

A

Np/Ns
260/130
2:1

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10
Q

A transformer has a turns ratio of 5:1 if the secondary current is 24A what is the primary current?

A

Ip/Is = Ns/Np
Ip/24 = 1/5
Ip= 24x1/5= 4.8A

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11
Q

Three types of Dc Motors

A

Series motors
Shunt motors
Compound motors

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12
Q

E =

A

I/d squared

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13
Q

How is electrical energy produced from a gas fired power station

A

Electrical energy is produced from a gas fire power station by the gas being burned which converts chemical energy to thermal which produces steam. The high pressure steam is fed into a steam turbine thermal energy is converted to mechanical energy, the turbine rotates an alternator which produces electrical energy

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14
Q

Voltage levels between a generating station and domestic premises

A

25kv—400kv/132kv—33kv/11kv—11kv—400V/230V

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15
Q

What is a UPS and why and where is it used

A

It is an Uninterruptible power supply and is used to prevent loss of supply in hospitals and large offices

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16
Q

What is meant by term heating zone

A

A heating zone is a designated area in a property that is usually controlled by a thermostat or a timer

17
Q

Types of losses in a transformer

A

Heat losses, Eddy currents losses occur in a transformer

18
Q

What is meant by true power
Useful

A

The power in an AC circuit that is transmitted to the load and does useful work it gets converted

19
Q

Apparent power is

A

supply voltage x supply current in an AC circuit

20
Q

Reactive power is

A

The useless power in an AC circuit. It does no useful work, but is necessary for the circuit to work.

21
Q

What does the curved section of the graph represent
(Curved thermal)

A

The curved section represents thermal operation of the mcb

22
Q

What does the straight section of the graph represent
(Straight magnetic)

A

The straight section represents magnetic operation of the MCB due to the solenoid

23
Q

Phase and line values of voltage are the same in

A

Delta VL=VP

24
Q

Phase and line values of current are the same in

A

Star IL=IP

25
Q

Types of split phase motors

A

Permanent capacitor motor
Capacitor start motor
Capacitor start and run motor

26
Q

Types of heating systems

A

S plan
Y plan
Underfloor heating

27
Q

Why is electrical energy transmitted at high voltages

A

It allows the voltages to be stepped up and down using transformers

28
Q

What are the advantages of electrical energy transmitted at high voltages

A

To improve efficiency
Less heat losses
To reduce current flow
Overcome voltage drop

29
Q

VP=

A

VL/square root 3

30
Q

Advantages of load balancing on three phase systems

A

Current taken by each line is also equal
Reduces current flow

31
Q

Disadvantages of DOL starters

A

Reduced lifespan of the machine

32
Q

Advantages of a soft starter

A

Smooth starting and stopping by torque control
Reduction in starting current
Reduce maximum demand

33
Q

Three losses in a TRANSFORMER

A

Copper losses, eddy current losses, hysterisis losses

34
Q

XL=

A

2PiFL

Electrical Science Exam (2 decks)

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