What causes counter emf in a dc motor

What causes counter emf in a dc motor
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Generator action.
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Related questions

What motor characteristic is affected by counter emf?

Description : What motor characteristic is affected by counter emf?

Last Answer : Speed.

The counter EMF of a DC motor is maximum when the _________. A. motor is at rated speed B. armature is not turning C. motor is almost up to rated speed D. armature has just begun to turn

Description : The counter EMF of a DC motor is maximum when the _________. A. motor is at rated speed B. armature is not turning C. motor is almost up to rated speed D. armature has just begun to turn

Last Answer : Answer: A

The counter EMF produced in the windings of a DC motor is 'zero' when the ____________. A. armature has just begun to turn B. armature is not turning C. motor is almost up to rated speed D. motor is at rated speed

Description : The counter EMF produced in the windings of a DC motor is 'zero' when the ____________. A. armature has just begun to turn B. armature is not turning C. motor is almost up to rated speed D. motor is at rated speed

Last Answer : Answer: B

What is meant by induced emf? By counter emf?

Description : What is meant by induced emf? By counter emf?

Last Answer : Induced emf is the emf which appears across a conductor when there is relative motion between the conductor and a magnetic field; counter emf is the emf induced in a conductor that opposes the applied voltage.

Which of the following types of DC motors has its field connected in parallel with its armature? A. Counter EMF B. Shunt C. Salient pole D. Series

Description : Which of the following types of DC motors has its field connected in parallel with its armature? A. Counter EMF B. Shunt C. Salient pole D. Series

Last Answer : Answer: B

Which of the following statements describes what will occur if the motor shown in the illustration is required to carry 150% of full load? EL-0056 A. The primary counter emf will be increased. B. The stator current will increase. C. The slip will decrease. D. The slip value, stator current curve, and torque curve will all coincide.

Description : Which of the following statements describes what will occur if the motor shown in the illustration is required to carry 150% of full load? EL-0056 A. The primary counter emf will be increased. B. ... slip will decrease. D. The slip value, stator current curve, and torque curve will all coincide.

Last Answer : Answer: B

An increase in the amount of current flow through the armature of a shunt motor is the final result of a/an _____________. A. increase in the load on the motor B. decrease in the load on the motor C. increase in counter EMF D. decrease in armature torque

Description : An increase in the amount of current flow through the armature of a shunt motor is the final result of a/an _____________. A. increase in the load on the motor B. decrease in the load on the motor C. increase in counter EMF D. decrease in armature torque

Last Answer : Answer: A

Armature reaction in a dc motor causes a shift of the neutral plane in which direction?

Description : Armature reaction in a dc motor causes a shift of the neutral plane in which direction?

Last Answer : Opposite the rotation.

Why back emf used for a dc motor? highlight its significance.

Description : Why back emf used for a dc motor? highlight its significance.

Last Answer : The induced emf developed when the rotating conductors of the armature between the poles of magnet, in a DC motor, cut the magnetic flux, opposes the current flowing through the conductor, when the ... speed of rotation of the armature conductors. In starting, the value of back emf is zero.

A 4 pole lap wound dc shunt motor rotates at the speed of 1500 rpm, has a flux of 0.4 mWb and the total number of conductors are 1000. What is the value of emf? (A) 100 Volts. (B) 0.1 Volts. (C) 1 Volts. (D) 10 Volts.

Description : A 4 pole lap wound dc shunt motor rotates at the speed of 1500 rpm, has a flux of 0.4 mWb and the total number of conductors are 1000. What is the value of emf? (A) 100 Volts. (B) 0.1 Volts. (C) 1 Volts. (D) 10 Volts.

Last Answer : Ans: D Given N = 1500 rpm, Φ = 0.4 mWb, Z = 1000, P = 4, & A= 4 Therefore, Eb = NΦPZ / 60 A = 1500 x 0.4 x 4 x 1000 x 10^-3 / 60 x 4 = 60/6 = 10 volts

What is back emf in DC motor? Explain its significance.

Last Answer : Back emf: When the armature of DC motor rotates under the fixed magnetic field and cuts it, by Faraday's law an emf is induced in them. The induced emf acts in opposite direction to the ... the flow of armature current i.e. it automatically changes the armature current to meet load requirements. 

A single-phase half-controlled rectifier is driving a separately excited dc motor. The dc motor has a back emf

Description : A single-phase half-controlled rectifier is driving a separately excited dc motor. The dc motor has a back emf constant of 0.5 V/rpm. The armature current is 5 A without any ripple. The armature resistance is 2 Ohm. The ... of the motor will be  (A) 339 rpm (B) 359 rpm (C) 366 rpm (D) 386 rpm

Last Answer : 359

In the illustration, the diode between terminals 16 and 17 is to _________. EL-0046 A. insure that the voltage across the governor coil (EG-3P) never exceeds .6 VDC B. compensate for the temperature difference of the governor oil heating up C. protect the electronic governor from counter EMF D. act as a filter to prevent hunting

Description : In the illustration, the diode between terminals 16 and 17 is to _________. EL-0046 A. insure that the voltage across the governor coil (EG-3P) never exceeds .6 VDC B. compensate for the ... heating up C. protect the electronic governor from counter EMF D. act as a filter to prevent hunting

Last Answer : Answer: C

The ratio of the effective value of the counter EMF in volts, to the effective value of the current in amperes is called _____________. A. impedance factor B. capacitive reactance C. inductive reactance D. root mean square

Description : The ratio of the effective value of the counter EMF in volts, to the effective value of the current in amperes is called _____________. A. impedance factor B. capacitive reactance C. inductive reactance D. root mean square

Last Answer : Answer: C

In the actuator arm assembly of a hard disk drive transport, what device can position the magnetic heads to the correct track of a hard disk more accurately than a dc stepper motor?

Description : In the actuator arm assembly of a hard disk drive transport, what device can position the magnetic heads to the correct track of a hard disk more accurately than a dc stepper motor?

Last Answer : Voice coil servo.

What part of a floppy disk drive transport uses a dc stepper motor to position the magnetic heads over the recording surface of a floppy disk?

Description : What part of a floppy disk drive transport uses a dc stepper motor to position the magnetic heads over the recording surface of a floppy disk?

Last Answer : Actuator arm assembly.

In a dc motor that must be able to rotate in both directions, how is the direction changed?

Description : In a dc motor that must be able to rotate in both directions, how is the direction changed?

Last Answer : By reversing either field or armature connections

What is the load on a dc motor?

Description : What is the load on a dc motor?

Last Answer : The device to be driven by the motor.

What are the differences between the components of a dc generator and a dc motor?

Description : What are the differences between the components of a dc generator and a dc motor?

Last Answer : There are no differences.

What factors determine the direction of rotation in a dc motor?

Description : What factors determine the direction of rotation in a dc motor?

Last Answer : Direction of armature current, and direction of magnetic flux in field.

What is the effect of motor reaction in a dc generator?

Description : What is the effect of motor reaction in a dc generator?

Last Answer : A force which causes opposition to applied turning force.

What causes dc bias energy to be absorbed by avalanche electrons and given up to the microwave field applied to an avalanche transit-time diode?

Description : What causes dc bias energy to be absorbed by avalanche electrons and given up to the microwave field applied to an avalanche transit-time diode?

Last Answer : The negative-resistance property.

What component causes a generator to produce dc voltage rather than ac voltage at its output terminals?

Description : What component causes a generator to produce dc voltage rather than ac voltage at its output terminals?

Last Answer : A commutator

What is the name of the emf generated in the primary that opposes the flow of current in the primary?

Description : What is the name of the emf generated in the primary that opposes the flow of current in the primary?

Last Answer : . Self-induced or counter emf

What term describes voltage or emf?

Description : What term describes voltage or emf?

Last Answer : Difference of potential.

An emf is generated in a conductor when the conductor is cut by what type of field?

Description : An emf is generated in a conductor when the conductor is cut by what type of field?

Last Answer : Magnetic field.

Why is no emf induced in a rotating coil when it passes through the neutral plane?

Description : Why is no emf induced in a rotating coil when it passes through the neutral plane?

Last Answer : No flux lines are cut.

What rule should you use to determine the direction of induced emf in a coil?

Description : What rule should you use to determine the direction of induced emf in a coil?

Last Answer : The left-hand rule for generators.

What is the emf equation for DC generator?

Description : What is the emf equation for DC generator?

Last Answer : A = number of parallel paths. That is for lap winding it is equal to Z and for wave winding it equal to 2. 

Explain concept of back emf in DC machine. State how it governs armature current.

Description : Explain concept of back emf in DC machine. State how it governs armature current. 

Last Answer : Back emf: When the armature of DC machine rotates under the influence of driving torque, the armature conductors move in the magnetic field and cut it and hence emf is induced in them. The ... flow of armature current i.e. it automatically changes the armature current to meet load requirements.

The induced emf in the armature of a lap -wound four -pole dc machine having 100 armature conductors

Description : The induced emf in the armature of a lap -wound four -pole dc machine having 100 armature conductors rotating at 600 rpm and with 1 Wb flux per pole is  (1) 1000V (2) 100V (3) 600V (4) 10,000V

Last Answer : The induced emf in the armature of a lap -wound four -pole dc machine having 100 armature conductors rotating at 600 rpm and with 1 Wb flux per pole is 1000V

A synchronous motor maintains synchronism with the rotating field because _____________. A. field strength varies directly with rotor slip B. DC current applied to the rotor coils causes the rotor magnets to lock in with the rotating flux of the stator C. the stator poles are dragged around due to the flux created by the excitation current D. the stator flux rotates in the opposite direction

Description : A synchronous motor maintains synchronism with the rotating field because _____________. A. field strength varies directly with rotor slip B. DC current applied to the rotor coils causes the rotor ... the flux created by the excitation current D. the stator flux rotates in the opposite direction

Last Answer : Answer: B

A DC Motor develops a torque of 150 N-m. A 10 percent reduction in the field flux causes a 50 percent

Description :  A DC Motor develops a torque of 150 N-m. A 10 percent reduction in the field flux causes a 50 percent increase in armature current. The new value of torque is: A) 102.5 N-m B) 202.5 N-m C) 172.5 N-m D) 232.5 N-m

Last Answer : T1=KIf,T2=K1.5I*0.9f T1=150Nm.  T2=T1*1.5*0.9=150*1.35=202.5Nm

When a motor is just started, back emf is almost ______: a. Infinite b. zero c. minimum d. maximum

Description : When a motor is just started, back emf is almost ______: a. Infinite b. zero c. minimum d. maximum

Last Answer : d. maximum

If the motor is overloaded, then the magnitude of ‘back emf’” a. Increases b. Decreases c. Constant d. Becomes zero

Description : If the motor is overloaded, then the magnitude of ‘back emf’” a. Increases b. Decreases c. Constant d. Becomes zero

Last Answer : Increases

The back emf of synchronous motor depends on?

Description : The back emf of synchronous motor depends on?

Last Answer : The back emf of synchronous motor depends on load angle.

What is the difference between a positive counter and a step counter?

Description : What is the difference between a positive counter and a step counter?

Last Answer : The load resistor in a positive counter is replaced by a capacitor in a step counter.

How do uhf tubes counter the effects of transit time?

Description : How do uhf tubes counter the effects of transit time?

Last Answer : By reducing the spacing between tube elements.

What is the largest count that can be indicated by a four stage counter?

Description : What is the largest count that can be indicated by a four stage counter?

Last Answer : 11112, or 1510.

. What type of counter has clock pulses applied to all FFs?

Description : . What type of counter has clock pulses applied to all FFs?

Last Answer : Synchronous.

An asynchronous counter is also called a ___________ counter.

Description : An asynchronous counter is also called a ___________ counter.

Last Answer : Ripple

What is the modulus of a five-stage binary counter?

Description : What is the modulus of a five-stage binary counter?

Last Answer : 32.

What is the function of the interpoles installed in DC motors? A. To provide greater torque by strengthening the main field. B. To provide sparkless commutation without having to shift the brushes. C. To limit the production of counter-electromotive force. D. To limit the starting surge current.

Description : What is the function of the interpoles installed in DC motors? A. To provide greater torque by strengthening the main field. B. To provide sparkless commutation without having to shift the brushes. C. To limit the production of counter-electromotive force. D. To limit the starting surge current.

Last Answer : Answer: B

An emf of 120 V causes a current of 3A to flow in a circuit how much energy is supplied by the source in..

Description : An emf of 120 V causes a current of 3A to flow in a circuit how much energy is supplied by the source in 12 seconds. A. 4130 J B. 4310 J C. 4320 J D. None of these 

Last Answer : An emf of 120 V causes a current of 3A to flow in a circuit how much energy is supplied by the source in 12 seconds.   4320 J

Circuits which maintain constant voltage or current outputs are called dc voltage or dc current ___.

Description : Circuits which maintain constant voltage or current outputs are called dc voltage or dc current ___.

Last Answer : Regulators.

What is the basic difference between the primaries of ac and dc rate generators?

Description : What is the basic difference between the primaries of ac and dc rate generators?

Last Answer : The method of primary excitation (ac and permanent magnet).

What two factors can cause output dc voltage to change?

Description : What two factors can cause output dc voltage to change?

Last Answer : Ac line voltage and a change in load resistance.

The electrons in the beam of a klystron are speeded up by a high dc potential applied to what elements?

Description : The electrons in the beam of a klystron are speeded up by a high dc potential applied to what elements?

Last Answer : The accelerator grid and the buncher grids.

Why does using ac vice dc bias voltage result in a stronger output signal?

Description : Why does using ac vice dc bias voltage result in a stronger output signal?

Last Answer : Because an ac bias voltage of the proper frequency and level places the input signal away from both steps in the magnetism curve. The result is two undistorted output signals that are combined into one strong output.

What are three advantages of adding an ac bias voltage to the input signal instead of adding a fixed dc bias voltage?

Description : What are three advantages of adding an ac bias voltage to the input signal instead of adding a fixed dc bias voltage?

Last Answer : a. Reproduces a stronger output signal. b. Greatly improves the SNR. c. Greatly reduces the natural tape hiss.