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100問 • 2年前

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If there is one power plant only, the installed capacity of that power plant should be equal to

Peak Load

If the air gap between the rotor and stator of a 3-phase induction motor is increases, then

Leakage reactance is increased

The 3-phase induction motor is so designed that the rotor should have

Low resistance

If the system is a three-wire system the currents flowing towards the load in the three lines must add to ___ at any given instant

Zero

If source impedance is complex, then maximum power transfer occurrs when thbload impedance is ______ the source of impedance.

Complex conjugate of

The starting torque of an induction motor is macimum when rotor resistance per phase is ____ to roto reactance/phase

Equal to

Which material is used in liquid type of fuse?

Carbon Tetra Chloride

Which of the following power plants cannot be used as base load plant?

Diesel elected plant

In an RC circuit, when the switch is closed, the response

Decays with time

The system supplying base and peak loas will be more economical if power is supplied by

Combines operation of various power plant

Which of the following is an essential requirement for a peak load plant?

Capability of quick start

For Zl = Zs, what is the relation between Xl and Xs

Xl=-Xs

The soeed of s squirrel cage induction motor is changed by

Pole changing method

Experiment A uses a test charge -2q to measure an electric field produced by stationary charges. A finds a field that is

The same both magnitude and direction as the field found by B

In the context of the lood and junction tules for electrical circuits, a junction is

Where three or more wires are joined

A battery has an emf of 9 V and an internal resistance of 2W. If the potential differences across its terminal is greater than 9 V

The current must be out of the negative terminal

Magnetization is

The magnetic dipole moment per unit volume of an object

Ferromagnetism is closely associated with

The tendency of electron dipole moments to align with each other

Paramagnetism is closely associated iwth

The tendency of electron dipole moments to align with an applied magnetic field

Of the following. The copper conductor that has the least resistance is

Thick, Short and Cool

“The sum of the currents into a junction equals to sum of the currents out of the junction” is a consequence of

Conservation of Charge

You wish to triple the rate of energy dissipation in a heating device. To do this you could triple

The resistance keeping the current the same

The RMS value of an ac current is

That steady state current that produces the same rate of heating in a resistor as the actual current

A toroid with a square cross section carries current i. The magnetic field has its largest magnitude

Just inside the toroid at its inner surface

If a circuit has L closed loops, B branches and J junctions, the number of independent loop equations is

B - J +1

For any circuit the nunber of independent equations containing emf’s, resistance and currents equals

The number of branches

If the potential differences across a resistor is doubled

Only the current is doubled

Faraday’s Law states that an induced emf is proportional to the

Rate of change of the magnetic flux

In a sinusoidally driven seriec RLC circuit, the inductive reactance is XL = 200 ohms, the capacitive reactance is XC = 100 ohms and the resistance is R = 50 ohms. The current and applied emf would be in phase if

The capacitance is halved with no other changes

A charged capacitor and an inductor are connected in series. At time t=0 the current is zero, but the capacitor is charged. If T is the period of the resulting oscillation, the next time after t=0 that the energy stored in the electric field of the capacitor is a maximum is

T/2

An initially uncharged capacitor C is connected in series with resistor R. This combination is then connected to a battery of emf V. Sufficient time elapses so that a steady state is reached. Which of the following is not true?

The total thermal energy generated by R is independent of R

A magnet moves inside a coil. Consider the following: I. Strength of the magnet II. Number of turns in the coil III. Speed at which the magnet moves Which can affect the emf induced in the coil?

I, II and III

The magnetic torque exerted on a flat current-carrying loop of wire by a uniform magnetic field B is

Maximum when the plane of the loop is parallel to B

Which is the core losses are negligible during a short-circuit test conducted on transformer?

The mutual flux is small

An LC series current with an inductance L and capacitance C has an oscillation frequency F. Two inductors, each with inductance L and 2 capacitors, each with capacitance C, are all wired in series and the circuit is completed. The oscillation frequency is:

A parallel plate capacitor with plates of area A that are separated a distance d by air is initially charged with charge qc. The energy stored in the capacitor initially is E. The plates are then separated by 2d. What is the new energy stored in the capacitor?

An electron traveling north enters a region where the electric field is uniform and points north

Slows down

The torque exerted by an electric field dipole is:

Perpendicular to both the field and dipole moment

1 weber is the same as:

1T m^2

The unity “henry” is equivalent to

Volt second/ ampere

The impedance of an RLC series circuit is definitely increased if:

R increases

A coil has a resistance of 5 ohms and an inductance of 1H. At t=0, it is connected to a 2V battery. Find the rate of rise of current when i=0.2 ampere

1A/ sec

Calculate the magnetic field intensity to produce a flux density of 10 x 10-3 tesla at the center of a long straight solenoid

7958 AT/m

What kind of rotor is most suitable for turbo-alternator which are designed to run at high speed?

Non-salient pole type

Which of the following types of motor is used in electric toys?

Shaded pole motor

When a dc motor has no load, what will happen to the back emf?

Becomes maximum

Which of the following is not a method of measuring the slip of an induction motor?

Magnetizing method

Synchronizing power of a synchronous machine is:

Inversely proportional to the synchronous reactance

A device that repeatedly reverses the polarity of a magnetic field in order to keep a dc motor rotating is known as:

A commutator

Which of the following is not a method of measuring the slip of an induction motor?

Magnetizing method

The transient voltage that appears across the contacts at the instant of arc extinction is called

Restriking voltage

A golf ball is struck by a golf club and falls on a green three meters above the tee. The potential energy of the earth-ball system is greatest

When the ball reaches the highest point

A generating station is to supply four regions of load whose peak loads are 10 MW, 5 MW, 8 MW, 7 MW. The diversity factor is 1.5 and the average annual load factor is 60. Calculate the annual energy supplied by the station

105.12 x 10 6 kWHR

Silica gel prevents air moisture from entering the outdoor transformer tank. It is placed on

Breather

A three phase transposed distribution line is designed with equilateral spacing of 12 ft. It is decided to build the line with horizontal spacing (D13=2D12=2D23). The conductors are transposed. What should be the spacing between adjacent conductors in order to obtain the same inductance as in the original design?

9.5246

A three phase transmission line is 30 km long. The outside diameter of the conductor is 0.721 inch and has an equilateral spacing of 4 ft. Determine the capacitance per phase of the line

0.341 uF

Tall growing plants refer to plants, vines and other plants species, which grow or have the potential to grow more than ___ in height from the ground

3 m

It is hereby declared unlawful for any person, whether natural or judicial, public or private, to:

All of the answers

For an unbalanced load, which connection is suitable?

4 wire wye connection

Which of the following statements about induction motor is FALSE

They are used to increase the line power factor

What is the period of oscillation of the position given as x(t) = -0.25 cos 16.05t

0.3915 s

The units of electric field are

N/C

In a dc motor, the mechanical output power actually comes from

Electrical input power

Recombination takes place when:

An electron falls into a hole

Large capacity generators are invariably

hydrogen cooled

In practice, regenerative braking is used when

load has overhauling characteristics

If an intrinsic semiconductor is doped with a very small amount of boron, then in the extrinsic semiconductor so formed, the number of electrons and holes will

decrease and increase respectively

When the interconnector between two stations is proportional to the current in that winding because

leakage paths do not saturate

The chief advantage of Ward-Leonard system of dc motor speed control is that is

gives smooth, sensitive and wide speed control

The primary function of a clamper circuit is to:

introduce a dc level into an ac signal

A 0-1 mA meter has a sensitivity of

1 kohm/V

The ordinary efficiency of a given transgormer is maximized when

its Cu loss equals iron loss

Which of the following is preferred when quick speed reversal is the main consideration

Synchronous motor

As compared to shunt and compound motors, a series motor has the highest torque because of its comparatively ___ at the start

stronger series field

Corona usually occurs when the electrostatic stress in air around the conductor exceeds

30 kV (maximum value)/ cm

If the height of the transmission tower is increased

The line capacitance will decrease but line inductance will remain unchanged

Which of the following dc motor would be suitable for drivers requiring high starting torque but only fairly constant speed such as crushers

Compound

A synchronous condenser is virtually which of the following?

Overexcited synchronous motor

The main disadvantage of Hopkinson’s test for finding efficiency of shunt dc motor is that it

requires two identical shunt machines

Maximum demand of an installation is given by its

average maximum demand over a definite interval of time during a certain period

For a consumer, the most economical power factor is generally

0.95 lagging

When a live conductor of public electric supply breaks down and touches the earth which of the following will happen?

Current will flow to earth

The energy of a magnetic dipole in an external magnetic field is least when:

the dipole moment is parallel to the field

The magnitude of the Bohr magneton in J/T is about:

10 -23

The maximum torque by dc motors is limited by:

commutation

The electric field in unpolarized light:

changes direction randomly and often

During the charging of a lead-acid cell:

Its voltage increases

The behavior of ferromagnetic domains in an applied magnetic field gives rise to:

hysterisis

The outer surface of the cardboard center of a paper towel roll:

cannot be a Gaussian surface because it is not a closed surface

The unit of absolute permittivity of a medium is:

Farad/meter

The molecular theory of magnetism can explain each of the following EXCEPT:

an N pole attracts a S pole

As compared to constant-current system, the constant-voltage system of charging a lead-acid cell has the advantage of:

Both Reducing time of charging and Increasing cell capacity

Two thin spherical shells, one with radius R and the other with radius 2R, surround an isolated charged point particle. The ratio of the number of field lines through the larger sphere to the number through the smaller is:

An isolated charged point particle produces an electric field with magnitude E at a point 2 m away from the charge. A point at which the field magnitude is E/4 is:

4 m away from the particle

_______ bridge is used for measuring an unknown inductance in terms of a known capacitance and resistance.

Anderson

Magnetization vectors in neighboring ferromagnetic domains are:

always in different directions

Ward-Leonard system of speed control is not recommended for:

constant speed operation

The magnetic dipole moment of an atomic electron is typically:

a few Bohr magnetons

The most efficient form of damping employed in electrical instruments is:

Eddy currents

100

A bar magnet is broken in half. Each half is broken in half again, etc. The observation is that each piece has both a north and south pole. Thus, usually explained by:A bar magnet is broken in half. Each half is broken in half again, etc. The observation is that each piece has both a north and south pole. Thus, usually explained by:

Ampere`s theory that all magnetic phenomena result from electric currents

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ユーザ名非公開 · 3回閲覧 · 100問 · 1年前

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問題一覧

If there is one power plant only, the installed capacity of that power plant should be equal to

Peak Load

If the air gap between the rotor and stator of a 3-phase induction motor is increases, then

Leakage reactance is increased

The 3-phase induction motor is so designed that the rotor should have

Low resistance

If the system is a three-wire system the currents flowing towards the load in the three lines must add to ___ at any given instant

Zero

If source impedance is complex, then maximum power transfer occurrs when thbload impedance is ______ the source of impedance.

Complex conjugate of

The starting torque of an induction motor is macimum when rotor resistance per phase is ____ to roto reactance/phase

Equal to

Which material is used in liquid type of fuse?

Carbon Tetra Chloride

Which of the following power plants cannot be used as base load plant?

Diesel elected plant

In an RC circuit, when the switch is closed, the response

Decays with time

The system supplying base and peak loas will be more economical if power is supplied by

Combines operation of various power plant

Which of the following is an essential requirement for a peak load plant?

Capability of quick start

For Zl = Zs, what is the relation between Xl and Xs

Xl=-Xs

The soeed of s squirrel cage induction motor is changed by

Pole changing method

Experiment A uses a test charge -2q to measure an electric field produced by stationary charges. A finds a field that is

The same both magnitude and direction as the field found by B

In the context of the lood and junction tules for electrical circuits, a junction is

Where three or more wires are joined

A battery has an emf of 9 V and an internal resistance of 2W. If the potential differences across its terminal is greater than 9 V

The current must be out of the negative terminal

Magnetization is

The magnetic dipole moment per unit volume of an object

Ferromagnetism is closely associated with

The tendency of electron dipole moments to align with each other

Paramagnetism is closely associated iwth

The tendency of electron dipole moments to align with an applied magnetic field

Of the following. The copper conductor that has the least resistance is

Thick, Short and Cool

“The sum of the currents into a junction equals to sum of the currents out of the junction” is a consequence of

Conservation of Charge

You wish to triple the rate of energy dissipation in a heating device. To do this you could triple

The resistance keeping the current the same

The RMS value of an ac current is

That steady state current that produces the same rate of heating in a resistor as the actual current

A toroid with a square cross section carries current i. The magnetic field has its largest magnitude

Just inside the toroid at its inner surface

If a circuit has L closed loops, B branches and J junctions, the number of independent loop equations is

B - J +1

For any circuit the nunber of independent equations containing emf’s, resistance and currents equals

The number of branches

If the potential differences across a resistor is doubled

Only the current is doubled

Faraday’s Law states that an induced emf is proportional to the

Rate of change of the magnetic flux

The capacitance is halved with no other changes

T/2

The total thermal energy generated by R is independent of R

A magnet moves inside a coil. Consider the following: I. Strength of the magnet II. Number of turns in the coil III. Speed at which the magnet moves Which can affect the emf induced in the coil?

I, II and III

The magnetic torque exerted on a flat current-carrying loop of wire by a uniform magnetic field B is

Maximum when the plane of the loop is parallel to B

Which is the core losses are negligible during a short-circuit test conducted on transformer?

The mutual flux is small

An electron traveling north enters a region where the electric field is uniform and points north

Slows down

The torque exerted by an electric field dipole is:

Perpendicular to both the field and dipole moment

1 weber is the same as:

1T m^2

The unity “henry” is equivalent to

Volt second/ ampere

The impedance of an RLC series circuit is definitely increased if:

R increases

A coil has a resistance of 5 ohms and an inductance of 1H. At t=0, it is connected to a 2V battery. Find the rate of rise of current when i=0.2 ampere

1A/ sec

Calculate the magnetic field intensity to produce a flux density of 10 x 10-3 tesla at the center of a long straight solenoid

7958 AT/m

What kind of rotor is most suitable for turbo-alternator which are designed to run at high speed?

Non-salient pole type

Which of the following types of motor is used in electric toys?

Shaded pole motor

When a dc motor has no load, what will happen to the back emf?

Becomes maximum

Which of the following is not a method of measuring the slip of an induction motor?

Magnetizing method

Synchronizing power of a synchronous machine is:

Inversely proportional to the synchronous reactance

A device that repeatedly reverses the polarity of a magnetic field in order to keep a dc motor rotating is known as:

A commutator

Which of the following is not a method of measuring the slip of an induction motor?

Magnetizing method

The transient voltage that appears across the contacts at the instant of arc extinction is called

Restriking voltage

A golf ball is struck by a golf club and falls on a green three meters above the tee. The potential energy of the earth-ball system is greatest

When the ball reaches the highest point

105.12 x 10 6 kWHR

Silica gel prevents air moisture from entering the outdoor transformer tank. It is placed on

Breather

9.5246

A three phase transmission line is 30 km long. The outside diameter of the conductor is 0.721 inch and has an equilateral spacing of 4 ft. Determine the capacitance per phase of the line

0.341 uF

Tall growing plants refer to plants, vines and other plants species, which grow or have the potential to grow more than ___ in height from the ground

3 m

It is hereby declared unlawful for any person, whether natural or judicial, public or private, to:

All of the answers

For an unbalanced load, which connection is suitable?

4 wire wye connection

Which of the following statements about induction motor is FALSE

They are used to increase the line power factor

What is the period of oscillation of the position given as x(t) = -0.25 cos 16.05t

0.3915 s

The units of electric field are

N/C

In a dc motor, the mechanical output power actually comes from

Electrical input power

Recombination takes place when:

An electron falls into a hole

Large capacity generators are invariably

hydrogen cooled

In practice, regenerative braking is used when

load has overhauling characteristics

If an intrinsic semiconductor is doped with a very small amount of boron, then in the extrinsic semiconductor so formed, the number of electrons and holes will

decrease and increase respectively

When the interconnector between two stations is proportional to the current in that winding because

leakage paths do not saturate

The chief advantage of Ward-Leonard system of dc motor speed control is that is

gives smooth, sensitive and wide speed control

The primary function of a clamper circuit is to:

introduce a dc level into an ac signal

A 0-1 mA meter has a sensitivity of

1 kohm/V

The ordinary efficiency of a given transgormer is maximized when

its Cu loss equals iron loss

Which of the following is preferred when quick speed reversal is the main consideration

Synchronous motor

As compared to shunt and compound motors, a series motor has the highest torque because of its comparatively ___ at the start

stronger series field

Corona usually occurs when the electrostatic stress in air around the conductor exceeds

30 kV (maximum value)/ cm

If the height of the transmission tower is increased

The line capacitance will decrease but line inductance will remain unchanged

Which of the following dc motor would be suitable for drivers requiring high starting torque but only fairly constant speed such as crushers

Compound

A synchronous condenser is virtually which of the following?

Overexcited synchronous motor

The main disadvantage of Hopkinson’s test for finding efficiency of shunt dc motor is that it

requires two identical shunt machines

Maximum demand of an installation is given by its

average maximum demand over a definite interval of time during a certain period

For a consumer, the most economical power factor is generally

0.95 lagging

When a live conductor of public electric supply breaks down and touches the earth which of the following will happen?

Current will flow to earth

The energy of a magnetic dipole in an external magnetic field is least when:

the dipole moment is parallel to the field

The magnitude of the Bohr magneton in J/T is about:

10 -23

The maximum torque by dc motors is limited by:

commutation

The electric field in unpolarized light:

changes direction randomly and often

During the charging of a lead-acid cell:

Its voltage increases

The behavior of ferromagnetic domains in an applied magnetic field gives rise to:

hysterisis

The outer surface of the cardboard center of a paper towel roll:

cannot be a Gaussian surface because it is not a closed surface

The unit of absolute permittivity of a medium is:

Farad/meter

The molecular theory of magnetism can explain each of the following EXCEPT:

an N pole attracts a S pole

As compared to constant-current system, the constant-voltage system of charging a lead-acid cell has the advantage of:

Both Reducing time of charging and Increasing cell capacity

An isolated charged point particle produces an electric field with magnitude E at a point 2 m away from the charge. A point at which the field magnitude is E/4 is:

4 m away from the particle

_______ bridge is used for measuring an unknown inductance in terms of a known capacitance and resistance.

Anderson

Magnetization vectors in neighboring ferromagnetic domains are:

always in different directions

Ward-Leonard system of speed control is not recommended for:

constant speed operation

The magnetic dipole moment of an atomic electron is typically:

a few Bohr magnetons

The most efficient form of damping employed in electrical instruments is:

Eddy currents

100

Ampere`s theory that all magnetic phenomena result from electric currents