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EE-II-UNIT 3-REVISION

Total questions: 100

Worksheet time: 51mins

Name
Class
Date
1.

If a transformer reduces voltage, it is called a....................... transformer.

a)

step left

b)

step right

c)

step up

d)

step down

2.

If a transformer increases voltage, it is called a ......... transformer.

a)

step right

b)

step left

c)

step up

d)

step down

3.

The winding of wire around a core which is connected to a source of energy is called the ....... coil.

a)

primary

b)

secondary

c)

tertiary

4.

Calculate potential difference in the secondary coil based on the information given below.


Vp = 240 V

Np = 20

Ns = 125

Vs ?

a)

1500

b)

500

c)

1000

d)

2000

5.

Which of the following is an example of appliance using alternating power source?

a)
b)
c)
d)
6.

Why transformers work with A.C. current but not D.C.

a)

A.C current produces changing magnetic field.

b)

D.C current produces changing magnetic field.

c)

D.C current is weak

d)

A.C current is powerful

7.

What is the material used for construction of transformer core?

a)

Aluminium

b)

Copper

c)

Iron

d)

Wood

8.

This picture is an example of a ________________.

a)

Motor

b)

Generator

c)

Step-up transformer

d)

Step-down transformer

9.

A transformer has 100 turns in the primary coil and 25 turns in the secondary coil. When a 120 V is applied to the primary coil, what is the voltage in the secondary coil?

a)

480V

b)

30V

c)

20V

d)

450V

10.

In order for electromagnetic induction to occur, there must be relative............between a magnetic field and a conductor.

a)

race

b)

Motion

c)

field

d)

voltage

11.

The transformer is a device used to .......... the value of a voltage.

a)

steady

b)

resist

c)

change

d)

anchor

12.

A laminated transformer core reduces the amount of energy that is wasted in the form of........

a)

solidifying

b)

flux

c)

heat

13.

Which of the following does not change in a transformer?

a)

Voltage

b)

Current

c)

Power

d)

Frequency

14.

Ratio of voltages is equal to ratio of _______________________.

a)

number of iron sheets in core

b)

number of coil

c)

number of turns in coil

d)

number of electromagnetic

15.

The function of a transformer is to ...

a)

raise and lower the apparent power levels

b)

transfer DC voltage from the primary winding to the secondary winding

c)

increase or decrease A.C voltage or A.C current levels

d)

transform mechanical energy into electrical energy

16.

The magnetic material for the core needs to be made of soft iron where its permeability is high

a)

to reduce eddy current loss

b)

to reduce hysteresis loss

c)

to avoid fringing in the core

d)

to reduce copper loss in the winding

17.

Transformer works on which of the following principle

a)

Lenz’s Law

b)

Ampere's Law

c)

Faraday's Law of Electromagenetic Induction

d)

Fleming's Law

18.

What is the meaning of transformer?

a)

Optimus Prime

b)

A device that transfers electrical energy from one circuit to another

c)

Autobots

d)

Megatron

19.

The thin sheets of steel from which transformer cores are made are called...................

a)

lamination

b)

transformer

c)

copper

20.

Transformer works on the principle of _________ .

a)

Self Induction

b)

Mutual Induction

21.

Transformer is always connected to ___________ supply.

a)

A.C.

b)

D.C.

22.

A transformer has primary voltage 200V and secondary voltage 100V , the transformer is called _______ .

a)

Step up

b)

Step Down

c)

None

23.

Transformer transforms _________ from primary to secondary.

a)

Only Current

b)

Only Voltage

c)

Both Voltage and Current

24.

Electrical symbol of a TRANSFORMER

a)
b)
c)
25.

The value of the second winding voltage of an iron-core transformer depends upon the ....... of turns, this winding contains as compared to the number of ........ winding turns.

a)

primary, size

b)

number, primary

c)

size, height

d)

number, size

26.

Primary winding of a transformer is determined by _________.

a)

which winding has more turns

b)

which winding is nearer to the load

c)

which winding is connected to the source

d)

which side has the highest voltage

27.

If a transformer is operated with direct current, the current must be ........ in value, or it must be broken up into pulses.

a)

weighty

b)

light

c)

changed

d)

heavy

28.

A Transformer is an example of a ........................... inductance

a)

mechanical

b)

electromagnetic

c)

transformer

29.

A transformer cannot deliver more..................to a load from its secondary winding than is supplied to the primary winding.

a)

electrololysis

b)

magnetism

c)

energy

30.

The unit of inductance is ......................

a)

henry

b)

pascal

c)

mm

31.

What is created continuously when current is flowing through the primary coil?

a)

changing magnetic field

b)

charging secondary coil

c)

step-up the secondary voltage

d)

increase the output power

32.

Which describe transformer

a)

Primary coil – receives input voltage

b)

Secondary coil – produces output voltage

c)

The voltage produced can either increases or decreases

33.

The voltage produced can either increases or decreases by altering

a)

input voltage

b)

output voltage

c)

number of turns of the primary coil

d)

number of turns of the secondary coil

34.

Two types of transformer are

a)

step-in transformer

b)

step-out transformer

c)

step-down transformer

d)

step-up transformer

35.

Name the type of transformer used in the diagram

(a)  

36.

For 2kVA 100/1000 V transformer, High voltage full rated current is

a)

20 A

b)

2 A

c)

200 A

d)

Can not be evaluated

37.

For a transformer copper losses are also known as

a)

variable loss

b)

iron loss

c)

eddy current loss

d)

losses in shunt parameter

38.

For a transformer, core losses are not equivalent to

a)

iron loss

b)

sum of eddy current losses and hysteresis losses

c)

losses in series parameters

d)

losses in shunt parameters

39.

In transformer which quantity do not remain same after transformer action at another winding end.

a)

magnetizing flux

b)

current

c)

kVA

d)

frequency

40.

Which one is true

a)

 MMF=FLUX×RELUCTANCEMMF=FLUX\times RELUCTANCE  

b)

 FLUX=MMF×RELUCTANCEFLUX=MMF\times RELUCTANCE  

c)

 RELUCTANCE=MMF×FLUXRELUCTANCE=MMF\times FLUX  

d)

 MMF=FLUX×NUMBER OF TURNS MMF=FLUX\times NUMBER\ OF\ TURNS\   

41.

Which one is true for E1 and E2

a)

Both are equal in magnitude as well as phase angle.

b)

Both are neither equal in magnitude nor in phase angle.

c)

Both are equal in magnitude but 90 degree apart to each other in phase angle.

d)

Both are equal in magnitude but 180 degree apart to each other in phase angle.

42.

Which one is not the condition for ideal transformer.

a)

Resistance of primary and secondary winding must be zero

b)

Leakage flux must be zero.

c)

Permeability must be zero.

d)

Eddy current and Hysteresis losses must be zero.

43.

Which one is not correct for auto transformer

a)

It has better voltage regulation in resistance and reactance of the single winding is less

b)

It has lower efficiency than two winding transformer.

c)

Used only for slight variation of the output voltage from input voltage

d)

It is also used as a voltage regulator

44.

HOW MANY WINDINGS ARE THERE IN AUTOTRANSFORMER?

a)

TWO

b)

ONE

c)

THREE

45.

AUTO TRANSFORMER WORKS ON -----------INDUCTION.

a)

SELF

b)

MUTUAL

c)

NONE

46.

APPLICATION OF CURRENT TRANSFORMER IS--------

a)

POTENTIAL TRANSFORMER

b)

CLAMP-ON METER

c)

CLIPPER

47.

ANOTHER NAME FOR POTENTIAL TRANSFORMER IS------------

a)

SERIES TRANSFORMER

b)

PARALLEL TRANSFORMER

c)

EQUAL TRANSFORMER

48.

ANOTHER NAME SERIES TRANSFORMER IS --------------

a)

POTENTIAL TRANSFORMER

b)

CURRENT TRANSFORMER

c)

PARALLEL TRANSFORMER

49.

EFFICIENCY OF COMMERCIAL TRANSFORMERS ARE ------

a)

0% TO 30%

b)

30% TO 79%

c)

95% TO 99%

50.

IDEAL TRANSFORMERS WILL HAVE ------ EFFICIENCY

a)

2%

b)

5%

c)

98%

d)

100%

51.

IN -------- TRANSFORMER LOSSES ARE ZERO.

a)

PRACTICAL

b)

IDEAL

c)

ISOLATION

52.

MARK THE REASON FOR CHOOSING SILICON STEEL AS CORE IN TRANSFORMER

a)

HIGH PERMEABILITY

b)

HIGH HYSTERESIS LOSS

c)

HIGH EDDY CURRENT LOSS

53.

POWER LOSSES ARE RISES -------- OF THE TRANSFORMER.

a)

VIBRATION

b)

TEMPERATURE

54.

Instrument transformers are used to ________________.

a)

transform mechanical energy into electrical energy.

b)

isolate or transform voltage or current levels.

c)

transfer DC voltage from the primary winding to the secondary winding.

d)

transfer DC current from the primary winding to the secondary winding.

55.

Which of the following is an instrument transformers?

a)

Potential transformers

b)

Current transformers

c)

All of the above

d)

None of the above

56.

What is a current transformer?

a)

A transformer that is used with an A.C. ammeter

b)

A transformer that is used with a D.C. ammeter

c)

A transformer that is used with an A.C. voltmeter

d)

A transformer that is used with a D.C. voltmeter

57.

What is a potential/voltage transformer?

a)

A transformer that is used with an D.C. ammeter

b)

A transformer that is used with an D.C. voltmeter

c)

A transformer that is used with an A.C. ammeter

d)

A transformer that is used with an A.C. voltmeter

58.

The primary winding of a C.T. has_________________.

a)

no number of turns at all

b)

a few number of turns

c)

a large number of turns

59.

The secondary winding of a C.T. has__________________. It is connected in _____________ to an ammeter.

a)

no number of turns at all, series

b)

a few number of turns, parelel

c)

a large number of turns, series

60.

The primary winding of a P.T. has ____________________.

a)

no number of turns at all

b)

a few number of turns

c)

a large number of turns

61.

The secondary winding of a P.T. has ____________________. A low range voltmeter is connected in _____________ with the secondary winding.

a)

no number of turns at all, series

b)

a few number of turns, parelel

c)

a large number of turns, series

62.

The potential transformers are used to measure large voltage using

a)

High range voltmeter

b)

Low range voltmeter

c)

High range ammeter

d)

Low range ammeter

63.

Select the facts about transformer.

a)

Will not work with DC and AC

b)

Will not work with DC

c)

AC will produce change in magnetic field

d)

AC will induce current

64.

Is the core insulated?

a)

Yes

b)

No

65.

The insulation at the transformer's core is meant for

a)

to avoid sharp edges.

b)

to avoid corrosion.

c)

to avoid electrical contact.

d)

to reduce power loss.

66.

Primary loop is connected to the supply while secondary loop is connected to the load.

a)

True

b)

False

67.

Step-up transformer is a transformer that increases...

a)

voltage.

b)

current.

c)

resistance.

d)

conductance.

68.

A secondary coil of a transformer has 500 windings. It was supplied with 200 V. How many windings needed at primary coil to produce 100 V.

(a)  

69.

A secondary coil of a transformer is supplied with voltage source, while the primary coil induces voltage (emf).

a)

True

b)

False

70.

Efficiency of a transformer is

a)

(output current)/(input current) x100%

b)

(output voltage)/(input voltage) x100%

c)

(output loss)/(input loss) x100%

d)

(output power)/(input power) x100%

71.

Efficiency of a transformer is

a)

(output current)/(input current) x100%

b)

(output voltage)/(input voltage) x100%

c)

(output loss)/(input loss) x100%

d)

(output power)/(input power) x100%

72.

A transformer has an output power of 500W. It also has core losses and copper loss of 10W. Determine the efficiency (%) of the transformer.

(a)  

73.

A transformer is 80% efficient with the primary voltage of 240 V and the secondary voltage of 12 V. If the current in the secondary circuit is 4 A, calculate the current in the primary circuit.

a)

6.50 A

b)

5.50 A

c)

1.00 A

d)

0.25 A

74.

Diagram shows a simple transformer with bulb lights up at normal brightness. What will happen if the alternating current, a.c input is replaced by a 3 V battery?

a)

The bulb blows

b)

The brightness of the bulb decreases

c)

The brightness of the bulb increases

d)

The bulb does not light up

75.

Ways to improve efficiency transformer

a)

Reduced heating effect in coil - using thicker wire made of good conductor like copper.

b)

Reduce eddy current - using laminated core.

c)

Increases magnetisation and demagnetisation - using Soft iron for core for easily magnetised (stronger magnetic field) and demagnetised

d)

increase leakage magnetic flux

- by winding secondary and primary coils on top each other.

76.

Ways energy losses

a)

Heating Effect in Coils (Resistance in coils)

b)

Eddy voltage in Iron Core.

c)

Magnetisation and Demagnetisation of Core.

d)

Leakage Magnetic Flux.

77.

Type of transformer is

a)

Step up

b)

Down up

78.

Diagram below shows a system for the transmission of electricity.

Which arrangement of transformers is correct?

a)
b)
c)
d)
79.

HOW WILL YOU REDUCE CORE LOSS IN THE TRANSFORMER?

a)

By using silicon steel

b)

By reducing the size of winding

c)

By increasing the size of the winding

80.

HOW WILL YOU FIND OUT THE CORE LOSS?

a)

BY CONDUCTING SHORT CIRCUIT TEST

b)

BY CONDUCTING OPEN CIRCUIT TEST

c)

BY MEASURING RESISTANCE OF THE WINDING

81.

SHORT CIRCUIT TEST IS USED TO FIND THE --------LOSS IN THE TRANSFORMER.

a)

CORE LOSS

b)

COPPER LOSS

c)

EDDY CURRENT LOSS

82.

THE TRANSFORMER IS A STATIC DEVICE.

a)

TRUE

b)

FALSE

83.

DIFFERENCE BETWEEN INPUT POWER TO OUTPUT POWER IS KNOWN AS ---------------

a)

GAIN

b)

LOSS

c)

CORE LOSS

d)

COPPER LOSS

84.

KVA STANDS FOR-----------------

a)

Kilo Volt Ampere

b)

Kilo Votage Ammeter

c)

Kilometer Volt Ammeter

85.

In a 3-phase, wye-connected system, the voltage values must be added vectorially because the coils are set 120 electrical degrees apart. In such an arrangement, the phase-to-phase voltage is obtained by multiplying the phase-to-neutral voltage by what multiplier? (select all that apply)

a)

0.58

b)

3.14

c)

1.73

d)

 3\sqrt{3}  

86.

The delta wiring configuration places each winding across the phase to phase source voltage. Therefore, the voltage across the winding will be equal to what value?

a)

the winding voltage multiplied by 125%

b)

zero

c)

the line voltage multiplied by 1.73

d)

the line voltage

87.

The transformer depicted in this photo is comprised of which of the following?

a)

A three-phase coil

b)

Three single-phase coils

c)

An oil-immersed coil

d)

One single-phase coil

88.

What type of connection if often used for distribution where a four-wire secondary distribution circuit is required?

a)

Wye-Wye

b)

Wye-Delta

c)

Delta-Wye

d)

Delta-Delta

89.

A 3-phase connection that has one end of each coil connected together and the other end of each coil left open for external connections is known as what?

a)

Delta

b)

Wye

c)

Flying V

d)

Auto

90.

A 3-phase connection method that has the wire from the ends of each coil connected end-to-end to form a closed loop is know as what?

a)

Wye

b)

Delta

c)

Flying V

d)

Auto

91.

The size of a transformer core will depend on

a)

(a) frequency

b)

(b) frequency and area of the core

c)

(c) flux density of the core material.

92.

If ∅m is the maximum value of flux in the core then the average rate of change of flux is

a)

a. f∅m

b)

b. 2 f∅m

c)

c. 4 f∅m

d)

d. 4.44 f∅m

93.

A Step-Up Transformer which has 110/220 turns.What would happen if we replace it with 10/20 turns? (because Turns ratio would be same in both cases)

a)

induced E.M.F wold be same

b)

Induced E.M.F would be decreased

c)

Induced E.M.F would be increased

d)

None of the above

94.

The rating of transformer may be expressed in ____________.

a)

kW

b)

KVA

c)

KVAR

d)

HORSE POWER

95.

Kindly mark the right answers

Transformer is --------

a)

Transfer Electrical power from one electrical circuit to another Electrical circuit It’s working without changing the frequency

b)

Work through on electro magnetic induction.

c)

When, both circuits take effect of mutual induction Can step up or step down the level of voltage.

d)

Its Working without changing the Power.

96.

Nominal ratio of an instrument transformer is defined as the

a)

reciprocal of the rated primary value

b)

ratio of rated secondary value to primary value

c)

reciprocal of the rated secondary value

d)

ratio of rated primary value to secondary value

97.

Winding resistance of a P.T. can be reduced by

a)

using thick conductors

b)

decreasing the length of the winding

c)

shorting the primary and secondary windings

d)

using thin conductors

98.

A transformer has 100 turns in the primary coil and 25 turns in the secondary coil. When a 120 V is applied to the primary coil, what is the voltage in the secondary coil?

a)

480V

b)

30V

c)

20V

d)

450V

99.

A transformer has 100 turns in the primary coil and 25 turns in the secondary coil. When a 120 V is applied to the primary coil, what is the voltage in the secondary coil?

a)

480V

b)

30V

c)

20V

d)

450V

100.

Which of the following is not a basic element of transformer?........

a)

Core

b)

Primary Winding

c)

Secondary Winding

d)

Mutual Flux

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