what is the difference between EMF and MMF ?

EMF stands for electro motive force,its the driving force required for the movement of electrons in an electrical circuit.

MMF stands for magneto motive force,it is the driving force required to drive the magnetic flux through a magnetic circuit.

Which type of A.C motor is used in the fan (ceiling fan, exhaust fan, padestal fan, bracket fan etc) which are find in the houses ?

Its Single Phase induction motor which mostly squirrel cage rotor and are capacitor start capacitor run.

If one lamp connects between two phases it will glow or not?

If the voltage between the two phase is equal to the lamp voltage then the lamp will glow. When the voltage difference is big it will damage the lamp and when the difference is smaller the lamp will glow depending on the type of lamp.

What are the differences between an alternator and a generator?

Alternator and generator, both devices have the same basic functionality. They both convert mechanical energy into electrical energy and they both have the same principal of electromagnetic induction. The main and only difference between these two devices lies in the construction. Alternator has a stationary armature and a rotating magnetic field for high voltages, while generator uses stationary magnetic field and rotating conductor which rolls on the armature with slip rings.

What is the difference between neutral and earth ?

• Neutral is a return current path for equipments ad earthing is protection for humans.
• Earth is a support for neutral.
• If neutral is not present,the equipment that we are using get in full phase and we will get a shock.so earthing is done to avoid such shocks.

Choose the correct one from among the alternatives A,B,C,D after matching an item from Group-1 with the most appropriate item in Group-2 (GATE-2004)

Choose the correct one from among the alternatives A,B,C,D after matching an item from
Group-1 with the most appropriate item in Group-2 (GATE-2004)

Group-1                                                               Group-2
P:Shift Register                                     1:Frequency Division Multiplexing
Q:Counter                                              2:Addressing in memory chips
R:Decoder                                              3:Serial to parallel data conversion


A) P-3,Q-2,R-1

B) P-3,Q-1,R-2

C) P-2,Q-1,R-3

D) P-1,Q-2,R-2

ANSWER:B

Why Delta/Star Transformers are used for Lighting Loads?

• Neutral conductor is must for lighting loads and hence the secondary of transformer must be a star winding

• To minimize the current unbalance in the primary we use delta winding in the primary so delta/star transformer is used for lighting loads

Why link is provided in neutral of an ac circuit and fuse in phase of ac circuit?

Neutral is the return path for current in an electrical circuit. So if you put a fuse on the neutral and link on the phase, then your equipment will burn before neutral fuse burn. That means no use and there won't be any protection for the equipment but you can use fuse on both if you want.but you are increasing the chance of circuit incompletion because in any case if neutral fuse disconnected you will lose the circuit. So no need of a fuse in the neutral.

What is the difference between 3-point & 4- point 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-).

Why in a three pin plug earth pin is thicker and longer than other two pins ?

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.

What is the rotor frequency at the slip of 10 percent?

What is the rotor frequency at the slip of 10 percent?

A. 10 Hz
B.2 Hz
C. 5 Hz
D. 50 Hz


AnS:  fr = sf = 0.1*50
           fr = 5Hz

A 4 pole D.C series motor at no load the speed will be

A 4 pole D.C series motor at no load the speed will be

A. 1500 rpm
B. 0 rpm
C. Very high
D. Vary between 1450 rpm to 1550 rpm.


Ans: Very high

What will happen if dc supply is given to primary of transformer ?

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.