Answer / satti

for a dc current it really flows.but in ac it just vibrate
of it .best example studying of semiconductor current flows

Answer / devsingh boda

I think in semi conductors electrons(Ex: In p-n junction diode some electrons cross the depletion layer) flows really whereas in pure conductors they only oscillate and just energy is transferred from one electron to the other.

Answer / tarun aggarwal ymca

Conductors have many, many mobile electrons. For many metals, it is about one electron per atom which is free to move. These electrons have rather large velocities, due to the fact that they fill up energy levels just as the electrons in atoms fill up available energy levels. When an electric field is applied, they are mobile and quickly move (average net motion, on top of their random motion) to cancel out the field, and so a good low-frequency approximation is that electric fields are always zero inside of conductors.

As you say, when a conductor carries a current, the electrons have a net drift velocity which is often quite small. The actual drift velocity depends a lot on the geometry of the conductor, the amount of current flowing, and the density of mobile charge carriers (the drift velocity is proportional to the current, and inversely proportional to the cross-sectional area and the density of mobile charge carriers). As you correctly say, in an AC circuit (with frequencies of 60 Hz here or 50 Hz where you are, or at radio frequencies), the electrons don’t drift very far. But what happens is that a large number of electrons all collectively shift their positions together. When you apply an electric field to a conductor, each electron only has to move a little bit, but all of them move together, and so the net current can be quite high.

Signals propagate along wires at very high speeds. If a wire is perfectly conducting, then the speed of a signal propagating along depends on the insulating material around the wire. This is because the energy transfer is actually in the electric and magnetic fields. Poynting’s vector is E cross B, and is proportional to the energy flow per unit area per unit time, and since the electric field vanishes inside a conductor, no energy flows inside a conductor (!), just outside, in the immediate vicinity. The speed of propagation of signals then depends on the dielectric properties of the insulation, and typically is about 70% of the speed of light. The electrons just flow in the conductor to satisfy the conditions of the electric and magnetic fields obeying Maxwell’s equations on the surface of the conductor.

About AC current -- the time average of the current in an AC circuit should be zero (unless there is some DC offset) -- current flows back and forth constantly, in response to alternating voltages. Many devices are perfectly happy to consume energy provided by AC circuits -- like light bulbs and toasters. Energy is deposited in the resistive elements of these items, independent of which way the current is flowing. The instantaneous power dissipated is V*I where V is the voltage between the light bulb's contacts and I is the instantaneous current. Since V=IR where R is the resistance of the light bulb, the power then is V2/R. To get the average power (wattage) for the light bulb, we just average V2 over time. Even if V is constantly switching sign, the power dissipated remains positive.

This is all a very classical answer to your question. In reality, all electrons are indistinguishable. It is not a fair question to ask about where a single electron goes as it does not retain its identity separate from the other electrons. But the classical picture is sufficient to explain the answers to these questions. One question it does not explain is why the electrons in metals are so mobile, and why they don’t bump into the atoms more, and quantum mechanics is needed for that one.

Answer / ymr

just vibrate at their position

Answer / ashok

the electorns are really flow that way say the current is flowing

what is tpdt

4 Answers  

hello everybody. please tell me the function of transformer bushing,s. i heared somewhere that it saved transformer winding from sky electricity. please tell me if that is right then how it work,s. Thank,s.

2 Answers   3EEE,

what is the use of neutral displacement relay

1 Answers   OCL,

does meager test perform on lightning arrester ? if doesn't then why ?

1 Answers  

what is the difference between gas group b and gas group c electrical equipment construction wise?

0 Answers  

What is the rating of HT SUBSTATION and LT SUBSTATION?

11 Answers   NTPC, Sail,

what is the benefit of floating our DC source? if i have two floating DC source of which 1 has a ref voltage of -21VDC and the other of -18VDC. can it be connected in parallel to share a common ref voltage? if not, how do i make both sources to be of common ref voltage? tks

0 Answers  

what's the meaning of the negative going half cycle in the circuit containing a bulb and a switch in series with a input ac source. i mean what happens in the -ve cycle. the dir. of current changes or any other thing. if dir. changes then why we use fuse in only phase wire.

2 Answers  

Amoung all types of short circuit faults in a transmission line which one has less number of occurance and why?

1 Answers  

How to calculate KW what is the formula for KW.

18 Answers   Toyota, UU,

We've 2 diffrent DG's with same capacity (500 KVA). Can we sync them ?

1 Answers  

what is meant by auto transformer?

4 Answers   Suzlon,