Question { 17400 }

why the capacitors works on ac only

Answer

Reactance of capacitor X = 1/(2πfc)

Since f=0, for dc frequency is zero.
So, Reactance X will be infinity for dc.

means capacitor blocks dc and allows only ac to pass

Question { 7719 }

Is earthing done for AC or DC or both?

Answer

for ac only guys..........dc has its own returning path
(called -ve terminal) it cant flow through earth untill
unless -ve terminal of dc source is earthed.

Question { 13364 }

Is possible to increase the voltage without using
transformer? why?

Answer

No...its not possible for AC. But we can increase DC
voltage using capacitor bank as mentioned above.

Question { ACC, 36865 }

Why dc supply is used for closing and tripping coil of ht
breakers. What happen if we use only ups ac supply only.

Answer

hey guys ....what a funny answers !!!! we have only two
extreams either open or closed. which can be serve by dc
only ..means if dc is given to trip coil,coil gets
magnetise in one direction.so that breaker gets opened.
Suppose if Ac would have been given two coil,magnetic
direction must gets changed according to frequency of
supply. So breaker starts to-n-fro motion. practically
there wont be any to-n-fro motin also because its frequency
is so high it will stay at same position. so it wont serve
the use of breaker.

Question { 7498 }

which type motor r use in the celling fan.....

Answer

Everybody has written correct answer .... So it is
Induction motor of squirrel cage type rotor with capacitor
start.

Question { Bhel, 9411 }

why there is a humming noise in transformer

Answer

Nilkanth Tailor's answer is correct

Question { IOCL, 53798 }

which motor is used in electric train...???????

Answer

I think, speed control is done by mechanical gear.I am not
so sure.

Question { 8348 }

the current which flows during lightening is ac or
dc,,,,,,,,,,, WHY

Answer

No dude ..its DC. when cloud is positively charged current
flows from cloud to earth as earth is at 0 potential. so
its unidirectional. sometimes when cloud is negatively
charged, current flows from earth to cloud. But its not
possible that same times same clouds gets + and - charged.
So at any instant current is from either cloud to earth or
earth to cloud. that is unidirectional. it does not changes
direction continuously for particular lightning.

Question { 6435 }

why we choose 50 or 60 hertz not other value for the power
system?

Answer

This is the standerds fixed once so that we can use all
apllainces without bouthering to change its
frequency.Otherwise we would have needed extra appaince
called frequency changer for all different application like
we use transformer as voltage changer.

Now question arise why 50 hz or 60 hz as standerds??
Because, Higher frequency generation needs high synchronous
speed which may results in mechanical instabilty of rotor.
and also may lead more friction loss.
Lower frequency may results in voltage fluctualtion which
will result in fluctuation in lights of bulbs. also it will
be very difficult to rectify in constant dc.

so we cant use very high frequency niether very low.. so
somewhat intermidiate value has been selected as 50 or 60
hz as standards.

we can use frequency between 40 hz to 75hz without having
any much damage. But once standards has decided so decided

Question { Bhel, 10363 }

what is electronics?

Answer

Branch of Physics where we study about the flow of electron
is called electrical and branch of electrical science where
we study about flow of electron through semiconductor and
vaccume tube, called electronics.
or we may say controlled flow of electron( since controlled
flow is possible only in semiconductor and vaccume tube).

so electronics is part of electrical,electrical is part of
physics

Question { 2679 }

why the dc level shifting is required inlinear intigrated
ckt?

Answer

An ideal integrated circuit should have output 0 in common
mode application( if differential input voltage is 0). But
practically its not like expected because of dissimilarity
in two transistor of integrated ckt. so we need put
additional dc voltage to compansate the dc level to 0 as
expected

Question { Wipro, 4021 }

DIFFERENC BETWEEN VOLTAGE AND CURRENT

Answer

flow of electron through conductor is called current.
the force or may say the cause responsible for flow of
current(electron),called voltage

means, Cause is voltage and result is current

Question { Bhel, 11729 }

What is ELCB?

Answer

“ Earth Leakage Circuit Breaker”. It is used to provide
protection of household circuit from leakage of current
through circuit to earth. Especially, it protects person who
is supposed to get shock while touching the faulty
appliances. Basically it measures difference in current
between “Live wire” & “Neutral wire”. If difference is 0,
fine. Else ELCB gets tripped. You must have noticed that,
difference won’t be zero iff current would have flown
through any person and felt shocked while touched the faulty
circuit. So, tripping of ELCB protects the person from
electric shock