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Electrical Fundamentals Worksheet (Translated)

Total questions: 100

Worksheet time: 50mins

Name
Class
Date
1.

What are the basic components of an electric circuit?

a)

Source – Load – Conductor

b)

Source – Switch – Lamp

c)

Conductor – Switch – Load

d)

Converter – Switch – Load

2.

An electric source is a device used to:

a)

Store energy

b)

Convert other forms of energy into electrical energy

c)

Consume electrical energy

d)

Increase voltage

3.

Electric current is defined as:

a)

Heat generated in a conductor

b)

Directed movement of electric charge

c)

Transmission capacity

d)

Change of current over time

4.

Formula for current:

a)

i = dq/dt

b)

i = U/R

c)

i = P/U

d)

i = L di/dt

5.

Voltage UAB is calculated as:

a)

UB − UA

b)

UA − UB

c)

U + I

d)

P/I

6.

P > 0 means:

a)

The branch delivers energy

b)

The branch consumes energy

c)

The source is off

d)

The circuit is open

7.

Resistance R characterizes:

a)

Ability to store energy

b)

Opposition to current

c)

Generation of magnetic field

d)

Generation of electric field

8.

Relationship for uR is:

a)

R/i

b)

R·i

c)

R/I2R/I^2

d)

U/I

9.

Inductive reactance XL equals:

a)

1/(ωC)

b)

ωL

c)

R + L

d)

ω/C

10.

Capacitive reactance XC equals:

a)

1/(ωC)

b)

ωL

c)

R·C

d)

I/U

11.

A power transmission system includes:

a)

Source – Inverter – Load

b)

Source – Transmission line – Load

c)

Load – Switch – Fuse

d)

Generator – Switch – Motor

12.

A disconnect switch is used to:

a)

Automatically protect against overload

b)

Manually switch small circuits

c)

Reverse motor direction

d)

Increase voltage

13.

When opening a disconnect switch, you should operate:

a)

Slowly to avoid arcing

b)

Quickly and decisively

c)

Pull the neutral first

d)

Close two poles in parallel

14.

The main function of a circuit breaker (aptomat) is:

a)

Manual switching

b)

Protection against overload and short circuit

c)

Increase power

d)

Create a magnetic field

15.

A contactor is a device for:

a)

Manual switching

b)

Remote, high-frequency switching

c)

Surge protection

d)

Voltage conversion

16.

The main contacts of a contactor are used to:

a)

Control small signals

b)

Switch the power circuit

c)

Hold a self-latching circuit

d)

Provide overvoltage protection

17.

A relay is a device that:

a)

Protects large currents

b)

Automatically switches small-power circuits

c)

Is only for household use

d)

Increases current

18.

The most important part of an electromagnetic relay is the:

a)

Spring

b)

Coil and magnetic circuit

c)

Contacts

d)

Adjustment knob

19.

A thermal relay operates based on:

a)

Electronics

b)

Mechanical force

c)

Thermal expansion of a bimetal strip

d)

Change of resistance

20.

A thermal relay protects against:

a)

Short circuit

b)

Overvoltage

c)

Motor overload

d)

Starting overcurrent

21.

A normally open (NO) pushbutton has the characteristic that:

a)

When pressed it opens

b)

When pressed it closes

c)

It is always closed

d)

It has no latching action

22.

A sensor is used to:

a)

Create a power signal

b)

Automatically compensate voltage

c)

Convert a physical quantity into an electrical signal

d)

Generate alternating current

23.

A fuse operates on the principle of:

a)

Melting of the fuse element due to Joule heating ( I2RI^2R )

b)

Magnetic attraction opening contacts

c)

A semiconductor cutting off at high voltage

d)

Cooling the conductor to interrupt current

24.

When there is a small and prolonged overload, which device acts?

a)

Fuse

b)

Circuit breaker

c)

Thermal relay

d)

Contactor

25.

The operating frequency of a contactor can reach:

a)

50 operations per hour

b)

500 operations per hour

c)

1500 operations per hour

d)

5000 operations per hour

26.

The coil of a contactor is used to:

a)

Reduce current

b)

Create magnetic pull

c)

Maintain the arc

d)

Switch auxiliary contacts

27.

An intermediate relay is used to:

a)

Increase voltage

b)

Switch large power

c)

Convert control signals

d)

Protect against short circuits

28.

A timer produces:

a)

Frequency

b)

On/off delay time

c)

Starting current

d)

Control voltage

29.

The rated current of a contactor is:

a)

The maximum continuous current the contacts can withstand

b)

Starting current

c)

Peak current

d)

Overload current

30.

A knife switch is commonly used in:

a)

Automatic control circuits

b)

Small circuits with infrequent operation

c)

High-frequency circuits

d)

Large motor circuits

31.

A purely inductive load has the characteristic:

a)

Power consists only of active power

b)

Contains only inductance L

c)

Stores energy in the electric field

d)

Current is in phase with voltage

32.

A purely capacitive load has the characteristic:

a)

Contains resistance

b)

Contains capacitance C

c)

Creates a magnetic field

d)

Current lags the voltage

33.

Conductance G equals:

a)

R

b)

1/R

c)

R2R^2

d)

1R2\frac{1}{R^2}

34.

Resistive power p equals:

a)

RI2RI^2

b)

R/IR/I

c)

UIUI

d)

LI2LI^2

35.

In a three-phase circuit, the line voltage equals:

a)

Phase voltage

b)

3\sqrt{3} times the phase voltage

c)

Half the phase voltage

d)

Three times the phase voltage

36.

In a star (Y) connection, the line current is:

a)

Id=3 IpI_d = \sqrt{3}\, I_p

b)

Id=IpI_d = I_p

c)

Ip=0I_p = 0

d)

Id=Ip/3I_d = I_p/\sqrt{3}

37.

In a delta (Δ) connection, the line current is:

a)

Id=IpI_d = I_p

b)

Id=3 IpI_d = \sqrt{3}\, I_p

c)

Id=Ip/3I_d = I_p/\sqrt{3}

d)

Id=0I_d = 0

38.

The phase voltage of a delta circuit is:

a)

Equal to the line voltage

b)

Zero

c)

Equal to line voltage divided by 3\sqrt{3}

d)

Three times the line voltage

39.

The most common three-phase load is:

a)

Electric stove

b)

Three-phase motor

c)

Capacitor bank

d)

Sensor

40.

A three-phase generator produces three electromotive forces that are:

a)

Equal amplitude and in phase

b)

Different amplitudes and 120° apart

c)

Equal amplitude and 120° apart

d)

90° apart

41.

If the direction of current is drawn opposite to reality in a circuit, what happens to the computed result?

a)

It cannot be computed

b)

It is completely wrong

c)

It is correct but the current carries a negative sign

d)

The current is always positive

42.

If U=0U = 0 but current is still not zero, which type of element is it?

a)

Resistor

b)

Inductor

c)

Capacitor

d)

Impossible

43.

When the current through an inductor increases rapidly, the voltage across the inductor will:

a)

Be zero

b)

Be proportional to the rate of increase of current

c)

Be opposite to the current direction

d)

Be independent of the current

44.

The energy stored in a capacitor is:

a)

12LI2\tfrac{1}{2}LI^2

b)

12CU2\tfrac{1}{2}CU^2

c)

UIUI

d)

RI2RI^2

45.

When frequency ff increases, which quantity increases?

a)

XLX_L

b)

XCX_C

c)

Resistance RR

46.

In a purely capacitive load circuit, the current is related to the voltage by which phase relationship?

a)

Lags the voltage by 90°

b)

Leads the voltage by 90°

c)

In phase with the voltage

d)

Lags the voltage by 45°

47.

In a purely inductive load circuit, the current is related to the voltage by which phase relationship?

a)

Lags the voltage by 90°

b)

Leads the voltage by 90°

c)

In phase with the voltage

d)

Equals zero

48.

For a purely resistive load, the reactive power Q equals:

a)

00

b)

RI2R I^2

c)

UIsin⁡φU I\sin\varphi

d)

Li2L i^2

49.

If R is doubled while U is kept constant, how does the consumed power change?

a)

Decreases by a factor of 2

b)

Decreases by a factor of 4

c)

Increases by a factor of 2

d)

Remains unchanged

50.

When a purely inductive load is connected to a DC source, the current:

a)

Rises immediately

b)

Does not increase

c)

Increases gradually following an exponential law

d)

Decreases gradually

51.

In an AC circuit, the active power is calculated by:

a)

P=UIP=UI

b)

P=UIcos⁡φP=UI\cos\varphi

c)

P=UIsin⁡φP=UI\sin\varphi

d)

P=I2ZP=I^2 Z

52.

In circuit modeling, a real source is replaced by:

a)

Only an electromotive force

b)

Only an internal resistance

c)

A voltage source in series with its internal resistance

d)

A series inductor

53.

The equivalent circuit of a DC motor load consists of:

a)

R in series with C

b)

E in series with R

c)

L in parallel with R

d)

An ideal DC source

54.

When a load has a low power factor, what happens?

a)

Current decreases

b)

Current increases

c)

Active power increases

d)

Losses decrease

55.

To reduce short-circuit current, one increases:

a)

Capacitance C

b)

Inductance L

c)

Resistance R

d)

Both R and L

56.

Arc formation during circuit interruption occurs because of:

a)

Low voltage

b)

High resistance

c)

Forced current through air

d)

High ambient temperature

57.

A contactor cannot open/close when:

a)

The coil loses power

b)

The overload is small

c)

The starting current increases

d)

The control circuit is open

58.

The normally closed (NC) auxiliary contact of a contactor is used to:

a)

Carry power

b)

Create a stop circuit

c)

Maintain self-hold

d)

Reverse motor direction

59.

The AC contactor coil usually has a shading ring in order to:

a)

Increase pull-in force

b)

Reduce noise and prevent chatter

c)

Reduce current

d)

Increase service life

60.

An electronic relay operates when:

a)

I>ItdI>I_{\mathrm{td}}

b)

U>UdmU>U_{\mathrm{dm}}

c)

Temperature rises

d)

Frequency increases

61.

A return coefficient Ktv closer to 1 means:

a)

The relay is less sensitive

b)

The relay is more sensitive

c)

The relay acts slower

d)

The relay has a large dropout

62.

In a thermal relay, the heating element serves to:

a)

Reduce current

b)

Generate heat to bend the bimetal strip

c)

Cool the contacts

d)

Limit arcing

63.

If the overload current is small but lasts a long time, which device acts first?

a)

Fuse

b)

Circuit breaker

c)

Thermal relay

d)

Contactor

64.

ON-delay timer means:

a)

Closes immediately upon receiving a signal

b)

Holds even if the signal is lost

c)

Closes after the preset delay

d)

Opens after the preset delay

65.

In a contactor, the main contacts are typically made of:

a)

Pure copper

b)

Silver alloy

c)

Aluminum

d)

Steel

66.

A contactor may have welded (stuck) contacts when:

a)

The overload is large

b)

Short-circuit current flows through the contacts

c)

The coil loses power

d)

Ambient temperature is low

67.

When selecting a circuit breaker (CB), choose:

a)

CB rated current < load current

b)

CB rated current = load current

c)

CB rated current > load current

d)

Independently of the load current

68.

The instantaneous action of a circuit breaker (CB) protects against:

a)

Overload

b)

Short circuit

c)

Phase loss

d)

Undervoltage

69.

An undervoltage trip of a circuit breaker operates when:

a)

the voltage falls below 85%

b)

the current increases

c)

the power increases

d)

the temperature increases

70.

An intermediate relay primarily serves to:

a)

switch a high-power circuit

b)

replicate a control signal

c)

provide short-circuit protection

d)

convert AC to DC

71.

In a three-phase system, if one phase is open (phase loss), the motor will:

a)

run normally

b)

speed up

c)

vibrate strongly, overheat, and may burn out

d)

reduce load but remain safe

72.

In a star connection, if the neutral conductor breaks:

a)

there is no effect

b)

phase voltages shift and can become dangerous

c)

the current decreases

d)

the load stops operating

73.

For an unbalanced three-phase load with a neutral present:

a)

the neutral current equals 0

b)

the neutral current is nonzero

c)

the line voltage changes

d)

it cannot be determined

74.

In a delta connection, the phase voltage equals:

a)

the line voltage

b)

the line voltage divided by 3\sqrt{3}

c)

0

d)

three times the line voltage

75.

In a delta circuit, the phase current equals:

a)

the line current

b)

the line current divided by 3\sqrt{3}

c)

3\sqrt{3} times the line current

d)

0

76.

The main function of the magnetic circuit in a contactor is to:

a)

dissipate heat

b)

carry magnetic flux

c)

suppress arcing

d)

reduce current

77.

When contacts are oxidized, the contact resistance:

a)

decreases

b)

increases, causing heating and potential fire

c)

does not change

d)

has no effect

78.

A latching (self-hold) pushbutton is used together with:

a)

a contactor’s NO auxiliary contact

b)

an NC auxiliary contact

c)

a timer

d)

a thermal relay

79.

For a motor started direct-on-line, the starting current is typically:

a)

2–3 times the rated current

b)

3–5 times the rated current

c)

5–7 times the rated current

d)

10 times the rated current

80.

In a reversing circuit using two contactors, it is not permitted to:

a)

wire the two coils in parallel

b)

energize both coils at the same time

c)

use interlocking contacts

d)

use an NC stop button

81.

At the instant when the current i=0i=0 , the energy stored in an inductor is:

a)

W=12Li2W=\tfrac12 L i^2

b)

always zero

c)

depends on the voltage UU

d)

depends on frequency

82.

When a capacitor discharges, the current direction:

a)

is always opposite to the charging current

b)

is random

c)

depends on the polarity of the voltage across the capacitor

d)

is the same as the charging current

83.

With an AC source, the average real power in an ideal inductor equals:

a)

> 0

b)

< 0

c)

= 0

d)

depends on frequency

84.

As frequency becomes high, the impedance of a series R–L–C circuit tends to:

a)

approach a maximum limit

b)

decrease

c)

depend only on R

d)

increase because the inductor dominates

85.

At resonance in a series RLC circuit:

a)

Z=RZ=R

b)

Z=0Z=0

c)

Z=∞Z=\infty

d)

I=0I=0

86.

In a parallel RLC circuit, at resonance the current is:

a)

minimum

b)

maximum

c)

zero

d)

increases with R

87.

When R=0R=0 in a series RLC circuit:

a)

resonance cannot occur

b)

resonance still occurs

c)

the capacitor loses effect

d)

the inductance becomes infinite

88.

A high quality factor QQ implies:

a)

the circuit dissipates a lot of energy

b)

a sharper resonance

c)

a lower resonant frequency

d)

it is undefined

89.

In a power transmission system, increasing the transmission voltage aims to:

a)

reduce power

b)

increase current

c)

reduce I2RI^2R losses

d)

increase phase shift

90.

When the power factor cosφ decreases:

a)

the current decreases

b)

the current increases

c)

the real power increases

d)

the losses decrease

91.

The cause of phase shift in an inductive load is:

a)

the electric field

b)

a magnetic field that lags the current

c)

a magnetic field leading in phase

d)

measurement error

92.

A parallel circuit has the smallest total impedance when:

a)

RR is large

b)

LL is large

c)

one branch has a very small impedance

d)

the capacitor is small

93.

Khi hai contactor đảo chiều bị kích đồng thời:

a)

Mạch mất tải

b)

Mạch vẫn chạy bình thường

c)

Ngắn mạch ba pha → nổ CB

d)

Không tác động

94.

22. Rơ le trung gian dùng để:

a)

Đóng cắt tải

b)

Tăng dòng điều khiển

c)

Cách ly tín hiệu điều khiển

d)

Bảo vệ chạm đất

95.

Bộ ngắt hồ quang trong CB làm nhiệm vụ:

a)

Hạ nhiệt độ ngay lập tức

b)

Kéo dài hồ quang và dập nhanh

c)

Tăng lực hút

d)

Giảm dòng

96.

Nút nhấn dừng là NC vì

a)

Để tiết kiệm dây

b)

Nếu đứt dây → tự động dừng máy

c)

Ngăn điện áp cao

d)

Giảm sụt áp

97.

Timer OFF-delay nghĩa là:

a)

Có điện là trễ ON

b)

Mất điện vẫn giữ rồi mới nhả

c)

Luôn mở

d)

Luôn đóng

98.

Trong mạch khởi động sao – tam giác, contactor sao và tam giác:

a)

Có thể đóng đồng thời

b)

Phải có liên động cơ và điện

c)

Không cần timer

d)

Đấu nối trực tiếp

99.

Khi CB liên tục bị sập nhưng không quá tải:

a)

Lỗi dây trung tính

b)

Lỗi bộ bảo vệ từ

c)

Rò điện → CB chống dòng rò tác động

d)

Tiếp điểm dính

100.

Tiếp điểm phụ NC của contactor có vai trò:

a)

Tự giữ

b)

Liên động chống đóng trùng

c)

Truyền công suất

d)

Bảo vệ quá dòng

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