What is the difference between active and passive elements ?
An active element is one, which is capable of generating the energy on its own. Examples,transistor,current source , FET, ect.
A passive element is one, which is incapable of generating energy on its own. But it is capable of storing and dissipating energy.It always need some external source of power.Examples, resistor, capacitor, inductor, ect.
What is the relation between electrical and mechanical degree?
The relationship between mechanical and electrical degrees is
1 degree mechanical = (P/2) electrical degrees
Where P = no. of poles
i.e. for 1 deg of mechanical revolution of conductor inside a magnetic field produces (P/2) degree electrical output.
Why is a shunt motor called constant speed motor ?
In dc shunt motor flux produced by field winding is proportional to field current Ish. Here the input voltage is constant so field current and flux is also constant.Therefore, dc shunt motor is also called a constant flux or constant speed motor.
Why the impedance of an voltmeter should be high as possible?
The impedance of an voltmeter should be as high as possible because voltmeter connected in parallel to the circuit for measuring voltages it does not take appreciable current.
How would you reverse the direction of rotation of a capacitor start-induction-run motor ?
The direction of rotation of a capacitor start-induction-run motor can be changed by either reversing the running or starting winding leads.but both must not be reversed.
Why BJT is called current controlled device and FET is called voltage controlled device ?
BJT is a current controlled device because input current controls output current.
FET is voltage controlled device because input voltage (Vgs) controls drain current (Id).
What is the difference full pitch and short pitch winding ?
Full pitch:
if coil span of winding is equal to pole pitch (180 deg),then it is said to be full pitch as shown in fig (a)
Short pitch:
if coil span of a winding is less than pole pitch (180 deg), then it is said to be short pitch as shown in fig (b). i.e coil span = 180-alpha,where alpha= angle of short pitch.
What is the difference between holding current and latching current of SCR ?
What is the necessity of starter in DC motor ?
The voltage equation of dc motor is
V = Eb + IaRa
at start Eb = 0, V= IaRa
Ia = V / Ra. (Ra alone limits the Ia)
generally motor is switched on with normal voltage and Ra is very small, the Ia at start is very high.This will blow out the fuses and may cause permanent mechanical damage to the motor.To limit this starting current to a safe value a variable resistance is connected in series with armature.This resistance is called as starter.
What is the difference between 3-point & 4- point starter ?
The basic difference between between 3-point and 4-point starter is the connection of no volt coil(NVC).
In 3-point starter NVC is connected in series with field winding, while in 4-point starter NVC is connected independently across the supply through fourth terminal called (L-).
How the direction of rotation of a dc motor can be reversed ?
The direction of a dc motor can be reversed either by reversing current through field winding or armature winding . Usually current through armature will be reversed.
Why dc series motor cannot be started without any load ?
In dc series motor,flux is directly proportional to armature current.under no load condition, the armature current is very low and flux also be less.By using formula N ∞ 1 / Ø , here
Ø is less,the motor speed will be very high.Due to this motor will be damaged.Hence DC series motor should always be started with some load on the shaft.
Why in a three pin plug earth pin is thicker and longer than other two pins ?
Resistance, R=pL/A
Where R= resistance
p= resistivity of the material
L= area of cross-section of wire
A is inversely proportional to R, so if A increases R decreases,so leakage current will easily take low resistance path.(this is the reason to make earth pin thicker)
For safety purpose it is made longer because the first to make connection and last to disconnect should be earth pin.it assures safety for the person who uses that equipment.
An active element is one, which is capable of generating the energy on its own. Examples,transistor,current source , FET, ect.
A passive element is one, which is incapable of generating energy on its own. But it is capable of storing and dissipating energy.It always need some external source of power.Examples, resistor, capacitor, inductor, ect.
What is the relation between electrical and mechanical degree?
The relationship between mechanical and electrical degrees is
1 degree mechanical = (P/2) electrical degrees
Where P = no. of poles
i.e. for 1 deg of mechanical revolution of conductor inside a magnetic field produces (P/2) degree electrical output.
Why is a shunt motor called constant speed motor ?
In dc shunt motor flux produced by field winding is proportional to field current Ish. Here the input voltage is constant so field current and flux is also constant.Therefore, dc shunt motor is also called a constant flux or constant speed motor.
Why the impedance of an voltmeter should be high as possible?
The impedance of an voltmeter should be as high as possible because voltmeter connected in parallel to the circuit for measuring voltages it does not take appreciable current.
How would you reverse the direction of rotation of a capacitor start-induction-run motor ?
The direction of rotation of a capacitor start-induction-run motor can be changed by either reversing the running or starting winding leads.but both must not be reversed.
Why BJT is called current controlled device and FET is called voltage controlled device ?
BJT is a current controlled device because input current controls output current.
FET is voltage controlled device because input voltage (Vgs) controls drain current (Id).
What is the difference full pitch and short pitch winding ?
Full pitch:
if coil span of winding is equal to pole pitch (180 deg),then it is said to be full pitch as shown in fig (a)
Short pitch:
if coil span of a winding is less than pole pitch (180 deg), then it is said to be short pitch as shown in fig (b). i.e coil span = 180-alpha,where alpha= angle of short pitch.
What is the difference between holding current and latching current of SCR ?
Holding current
|
Latching current
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Holding current is associated with turn-off process of SCR
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Latching current is associated with turn-on process of SCR
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Thyristor can be
turned-off or returned to forward blocking state only if the forward current
falls below a low level current called the holding current.
|
It is the minimum value of anode current Which it must attain during
turn-on process to maintain conduction when gate pulse is removed.
|
Holding current is less than the latching current.
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Latching current is the 2 to 3 times of holding current.
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What is the necessity of starter in DC motor ?
The voltage equation of dc motor is
V = Eb + IaRa
at start Eb = 0, V= IaRa
Ia = V / Ra. (Ra alone limits the Ia)
generally motor is switched on with normal voltage and Ra is very small, the Ia at start is very high.This will blow out the fuses and may cause permanent mechanical damage to the motor.To limit this starting current to a safe value a variable resistance is connected in series with armature.This resistance is called as starter.
What is the difference between 3-point & 4- point starter ?
The basic difference between between 3-point and 4-point starter is the connection of no volt coil(NVC).
In 3-point starter NVC is connected in series with field winding, while in 4-point starter NVC is connected independently across the supply through fourth terminal called (L-).
How the direction of rotation of a dc motor can be reversed ?
The direction of a dc motor can be reversed either by reversing current through field winding or armature winding . Usually current through armature will be reversed.
Why dc series motor cannot be started without any load ?
In dc series motor,flux is directly proportional to armature current.under no load condition, the armature current is very low and flux also be less.By using formula N ∞ 1 / Ø , here
Ø is less,the motor speed will be very high.Due to this motor will be damaged.Hence DC series motor should always be started with some load on the shaft.
Why in a three pin plug earth pin is thicker and longer than other two pins ?
Resistance, R=pL/A
Where R= resistance
p= resistivity of the material
L= area of cross-section of wire
A is inversely proportional to R, so if A increases R decreases,so leakage current will easily take low resistance path.(this is the reason to make earth pin thicker)
For safety purpose it is made longer because the first to make connection and last to disconnect should be earth pin.it assures safety for the person who uses that equipment.
how the emf will be developed when conductor the flux
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