Showing posts with label eee lab viva questions. Show all posts
Showing posts with label eee lab viva questions. Show all posts
Saturday, October 10, 2015
What is the difference between static and dynamically induced EMF ?
Statically induced EMF:
It is an emf induced without a relative motion between a conductor and magnetic field
Example: EMF induced in transformer
Dynamically induced EMF:
It is an emf induced with a relative motion between a conductor and magnetic field
Example: EMF induced in generator
It is an emf induced without a relative motion between a conductor and magnetic field
Example: EMF induced in transformer
Dynamically induced EMF:
It is an emf induced with a relative motion between a conductor and magnetic field
Example: EMF induced in generator
Tuesday, September 15, 2015
Friday, August 14, 2015
what is the difference between core and shell type transformer ?
S.No
|
Core type transformer
|
Shell type transformer
|
1
|
Core is surrounded by winding
|
Winding is surrounded bycore
|
2
|
It has two limbs
|
It has three limbs
|
3
|
It is made up of two L shaped strips
|
It is made up of E and I shaped strips
|
4
|
Easy to dismantle the windings for repair work
|
Difficult to dismantle the windings for repair work
|
5
|
Better heat dissipation
|
Poor heat dissipation as the winding is surrounded
by core.
|
Sunday, March 1, 2015
what are the biasing conditions for a transistor to act as an amplifier?
Region
|
Emitter base junction
|
Collector-base junction
|
function
|
Active
|
Forward biased
|
Reverse biased
|
Amplifier
|
Cut-off
|
Reverse biased
|
Reverse biased
|
Off-switch
|
saturation
|
Forward biased
|
Forward biased
|
On-switch
|
Saturday, February 28, 2015
Comparison between zener breakdown and avalanche breakdown
S.NO
|
Zener breakdown
|
Avalanche breakdown
|
1.
|
Breakdown is due to strong electric field developed
across the narrow depletion region.
|
Breakdown is due to charge multiplication
|
2.
|
Observed if Vz > 6 volt
|
Observed if Vz < 6 volt
|
3.
|
The VI characteristics is very sharp with zener
breakdown
|
The VI characteristics is not very sharp with
avalanche effect
|
4.
|
The breakdown voltage decreases as junction
temperature increases
|
The breakdown voltage increases as junction
temperature increases
|
5.
|
It occurs in heavly doped diodes
|
It occurs in normally doped diodes
|
Thursday, February 26, 2015
What is the difference between fuse and circuit breaker?
(i) Fuse performs both detection and interruption functions. Circuit breaker performs interruption function only. The detection of fault is made by relay system.
(ii) The breaking capacity of fuse is very small compare to that of circuit breaker.
(iii) The operating time of the fuse is smaller than operating time of CB.
(iv) After every operation, replacement is required in the fuse. In case of circuit breaker, replacement is not required.
Sunday, February 22, 2015
Comparison of PN junction diode and zener diode
Comparison of PN junction diode and zener diode
s.no
|
PN
junction diode
|
zener
diode
|
1
|
Symbol
 |
Symbol
 |
2.
|
Operated in forward biased condition
and never operated in reverse biased condition
|
Operated in reverse breakdown region
|
3
|
Characteristics lies in 1st quadrant
|
Characteristics lies in 3rd quadrant
|
4
|
Applications:
Rectifiers, clippers, clampers, voltage
multipliers
|
Applications:
Regulator, zener limiters
|
5
|
Low power dissipation capability
|
High power dissipation capability
|
Saturday, February 7, 2015
What is the necessity of starter in DC motor ?
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.
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.
Wednesday, January 21, 2015
What happens when a d.c motor is connected across an ac supply?
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.
Monday, January 19, 2015
Why transformers are rated in KVA and motors are rated in KW ?
The power factor of transformer is dependent on load we only
define Volt-ampere rating and does not include power factor but in case of motors,
power factor depend on construction and hence rating of motors is in
KW and include power factor.
Friday, January 16, 2015
What is hunting ?
What is hunting ?
- The oscillations of rotor due to sudden application or removal of load is called swinging or hunting.
- During hunting there are changes the current drawn by the motor which may cause problem to other appliances connected to the same line.Hence hunting is not desirable phenomenon from motor point of view and must be prevented.
Tuesday, January 13, 2015
What is the difference between unilateral and bilateral elements?
What is the difference between unilateral and bilateral elements?
Bilateral element: Voltage-current relation is the same for current flowing in either direction.
example: resistor,inductor and capacitor.
Unilateral element: different relations between Voltage and current for the two possible directions of current.
example: Vacuum tubes, silicon diodes, metal rectifiers ect.
Bilateral element: Voltage-current relation is the same for current flowing in either direction.
example: resistor,inductor and capacitor.
Unilateral element: different relations between Voltage and current for the two possible directions of current.
example: Vacuum tubes, silicon diodes, metal rectifiers ect.
Sunday, January 11, 2015
What is the difference between active and passive elements ?
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.
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.
Friday, January 9, 2015
Why field rheostat is kept in minimum position while armature rheostat is at maximum position ?
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.
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.
Wednesday, January 7, 2015
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.
Tuesday, January 6, 2015
Why is a shunt motor called constant speed motor ?
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.
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.
Saturday, January 3, 2015
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.
Friday, January 2, 2015
Define analog signal & digital signal.
- The amplitude of the signal varies continously with time.This signal is called analog signal.
- A signal defined at discrete instants of time is called digital signal.
Mention the applications of PN diode ?
- As switches
- As rectifiers
- Power supplies
- Clippers & Clampers
- Digital systems
- Communication systems
