work done by external source in moving a charge is negative if we move in the direction of E field.force is exerted on account of the field.does it imply that if the field is uniform then the charge will move an infinite distance in the direction of the field. If yes, then what is the amount of work done by an external source in the direction of E field? (This is no homework....i just got confused with the interpretation while going through the topic).Please clarify ....

 

It would not be infinite. I take the negative to mean that the work done comes from the field. Something has to generate the field and this would be the actual(positive) work done. The particle is able to move on its own due to the work input generating the field.

I don't think you can isolate one side of the equation and deduce infinity therefrom

 

Thanx for the quick response sir but i'm still not clear with it....uniform field exists for example in parallel plate capacitor directed from +ve to -ve. now if a positive charge is placed between the plates it will be pushed to the negative side. the movement will stop only when it reaches the negative plate and not anywhere in between the plates. in that essence can we not interpret a infinite displacement int the field direction due to the field itself. further, if a -ve charge was introduced it should move towards the +ve plate but this is as well opposing the uniform field direction so will it be able to move on its own in a direction opposing the field? i believe that since field lines dont cross so in this case we dont need to bother for the field due to the charge(point charge).I hope my confusion/query has been correctly put up....

 

i believe that since field lines dont cross so in this case we dont need to bother for the field due to the charge(point charge).

Science and particularly applied Science is not a question of belief, but of definition.

You should study whatever basic field theory material you have. Answering your question involves studying chapter 1 of your textbook.

To help us help you, what source material are you using, ie where is this coming from?

Do you understand simple integrals, you cannot do this without?

 

i am referring to Engineering electromagnetics by Hayt and Buck, The McGraw hill companies, Seventh edition....
My problem also lies in other thing....Flux in the book has unit coulomb. It says' for Faraday's experiment flux =Q andelectric flux is measured in coulomb'.....
whereas one old thread on this forum led me to
'Electrical flux has SI units of volt metres (V m), or, equivalently, newton metres squared per coulomb (N m2 C−1).'
Please recommend some good book(available in India) / online material for learning engineering electromagnetics so that i can clarify the doubts that i have as the fact is soon i have to teach this subject for the first time and am pretty confused myself.....Timely help and suggestions would be very much appreciated.......

 

Faraday's (ice pail?) experiment?

Sounds like you are teaching Physics?

You didn't answer my question about (simple) integration.

 

yes i do understand integrals....And if it sounds that i teach physics...maybe because the topics that i have to cover are primarily electrostatics, magnetostatics and maxwell's equations (time varying fields)....
work required to move the charge in the electric field is -Q*integral with limits as initial point to final point (E.dL)...E and dL are vectors...work is done if we move opposite to the field...no work if we move normal to the field.....now if we wish to move the charge in the same direction as E field do we do work...because the field itself tends to move the charge along its direction...I'm sure that the charge won't remain static in absence of external applied force that opposes the force due to field....
Please help clarify my doubt...i'm unable to proceed further....