What is the reason for current lagging the voltage in an inductive circuit?
In an ac circuit, the current is continously changing its direction of flow (50 times a second in a 50-hertz circuit). Any change of current value is opposed by the inductance within the circuit involved.
Why colour coding system is used to indicate the value of a resistor?
Some resistors are large enough in size to have their resistance values (in ) printed on the body. However there are some resistors, which are too small in size to have their resistance
values printed on them. Hence, a system of colour coding is employed for indicating their values.
Can you operate a cummulatively compounded generator as a differentially compound generator ? if so how ?
Cummulative compounded generator can be operated as differential compounded generator just by inter changing the terminal connections of series field winding.(Which changes the direction current flow in series field winding).
What is the difference between lightning arrestor and surge arrestor ?
Lightning arrestor is installed outside and the effect of lightning is grounded, where as surge arrestor is installed inside panels comprising of resistors which consumes the energy and nullify the effect of surge.
Why field rheostat is kept in minimum position while armature rheostat is at maximum position ?
At the time of starting of motor, the armature resistance is kept at maximum position to control and reduce the high starting current and field rheostat at minimum position to ensure that speed does not go beyond rated value and to have high starting torque.
What will happen if dc supply is given to primary of transformer ?
First of all, transformer wont work on dc supply and we wont get any induced emf in secondary because there won't be any change in flux with dc supply, hence there won't be faraday's law of electromagnetic induction.
With dc supply, there is no inductance only a small value of resistance will be offered,so the primary current will be quite high and much more than rated primary load current.This will burn the insulation of coil and transformer will be damaged.
Why a single phase induction motor is not self starting?
When the stator winding of a single phase induction motor is connected to a single phase ac supply,a magnetic field is developed, which is only alternating not a rotating field and this alternating flux acting on rotor cannot produce rotation,as it can be done only by rotating magnetic field(RMF).
According to double revolving field theory,this alternating flux can be resolved in to two components namely forward and backward component and both have same magnitude but rotating in opposite directions.say forward component tries to rotate the rotor in one particular direction ,then backward component tries to rotate it in opposite direction,hence the net torque developed at the timing of starting is zero.However, if the rotor is given a push by hand or by other means in either direction,it will pick-up the speed and continue to rotate in the same direction developing operating torque.Thus a single induction phase induction motor is not inherently self starting requires some special means for starting.
Why fuse is placed in phase not in neutral ?
The purpose of fuse to protect the equipment or the person who is handling the circuit from over current.If we put the fuse in neutral instead on phase,fuse will be blown off after that over current passing through that equipment but that circuit will not be isolated because of presence of fuse on neutral wire.This over current will still flow through the circuit and there wont be any safety and use of providing it on neutral.
What happens when a d.c motor is connected across an ac supply?
A 230 V supply is connected across series combination of two bulbs of 60W and 100W respectively.which bulb will glow bright and why ?
we know in series connection the current is same and voltage is different which depends on resistance of the individual elements connected.
P=V^2/ R, to maintain this relationship the resistance of 60W bulb is greater and voltage across 60 W bulb is more(V=IR).so 60W bulb will glow brighter than 100W bulb.
Why cannot a moving coil instrument be used in AC circuits ?
A moving coil instrument is used to measure d.c because it indicates the average value.In a.c, the deflecting torque of the instrument reverses if the current reverses and hence the pointer cannot follow the rapid reversals and the deflection corresponds to a mean torque value of zero.so these instruments cannot be used for a.c.
In an ac circuit, the current is continously changing its direction of flow (50 times a second in a 50-hertz circuit). Any change of current value is opposed by the inductance within the circuit involved.
Why colour coding system is used to indicate the value of a resistor?
Some resistors are large enough in size to have their resistance values (in ) printed on the body. However there are some resistors, which are too small in size to have their resistance
values printed on them. Hence, a system of colour coding is employed for indicating their values.
Can you operate a cummulatively compounded generator as a differentially compound generator ? if so how ?
Cummulative compounded generator can be operated as differential compounded generator just by inter changing the terminal connections of series field winding.(Which changes the direction current flow in series field winding).
What is the difference between lightning arrestor and surge arrestor ?
Lightning arrestor is installed outside and the effect of lightning is grounded, where as surge arrestor is installed inside panels comprising of resistors which consumes the energy and nullify the effect of surge.
Why field rheostat is kept in minimum position while armature rheostat is at maximum position ?
At the time of starting of motor, the armature resistance is kept at maximum position to control and reduce the high starting current and field rheostat at minimum position to ensure that speed does not go beyond rated value and to have high starting torque.
What will happen if dc supply is given to primary of transformer ?
First of all, transformer wont work on dc supply and we wont get any induced emf in secondary because there won't be any change in flux with dc supply, hence there won't be faraday's law of electromagnetic induction.
With dc supply, there is no inductance only a small value of resistance will be offered,so the primary current will be quite high and much more than rated primary load current.This will burn the insulation of coil and transformer will be damaged.
Why a single phase induction motor is not self starting?
When the stator winding of a single phase induction motor is connected to a single phase ac supply,a magnetic field is developed, which is only alternating not a rotating field and this alternating flux acting on rotor cannot produce rotation,as it can be done only by rotating magnetic field(RMF).
According to double revolving field theory,this alternating flux can be resolved in to two components namely forward and backward component and both have same magnitude but rotating in opposite directions.say forward component tries to rotate the rotor in one particular direction ,then backward component tries to rotate it in opposite direction,hence the net torque developed at the timing of starting is zero.However, if the rotor is given a push by hand or by other means in either direction,it will pick-up the speed and continue to rotate in the same direction developing operating torque.Thus a single induction phase induction motor is not inherently self starting requires some special means for starting.
Why fuse is placed in phase not in neutral ?
The purpose of fuse to protect the equipment or the person who is handling the circuit from over current.If we put the fuse in neutral instead on phase,fuse will be blown off after that over current passing through that equipment but that circuit will not be isolated because of presence of fuse on neutral wire.This over current will still flow through the circuit and there wont be any safety and use of providing it on neutral.
What happens when a d.c motor is connected across an ac supply?
- Since on ac supply, reactance will come in to play,the a.c supply will be offered impedance(not resistance) by the armature winding.consequently,with a.c supply,current will be much less.The motor will run but it would not carry the same load as it would on d.c. supply.
- There would be more sparking at the brushes
- Though motor armature is laminated as a rule, the field poles are not. consequently,eddy currents will cause the motor to heat up eventually burn on a.c. supply.
A 230 V supply is connected across series combination of two bulbs of 60W and 100W respectively.which bulb will glow bright and why ?
we know in series connection the current is same and voltage is different which depends on resistance of the individual elements connected.
P=V^2/ R, to maintain this relationship the resistance of 60W bulb is greater and voltage across 60 W bulb is more(V=IR).so 60W bulb will glow brighter than 100W bulb.
Why cannot a moving coil instrument be used in AC circuits ?
A moving coil instrument is used to measure d.c because it indicates the average value.In a.c, the deflecting torque of the instrument reverses if the current reverses and hence the pointer cannot follow the rapid reversals and the deflection corresponds to a mean torque value of zero.so these instruments cannot be used for a.c.
like this blog as it is informative...thank you..
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