IIT JEE , AIEEE Forum - Physics , Electricity

divalli_oct07

Q1) is the work done in an electrostatic field - always zero or zero at times?

Q2) what is uniform in a uniform electicfield -----potential , potential gradience , both or neither?

pls provide ans with reasons .

rphy

I'll try to answer ur 2nd question
Well in a uniform electric field basically the magnitude of all the electric field lines are the same. This means that ANYWHERE in the electric field region, the magnitude of the electric field will be the same.
Whereas in a non-uniform electric field the magnitude of the electric field is not the same at all places in the electric field region.

The electric potential always decreases in the direction of the electric field.

bhuvana89

ans1)

no it is not always 0....

there can be cases where it is 0 .......for example work done in moving a charge from one point to another in an equipotential surface is zero..

divalli_oct07

@rphy can u tell me what exactly is uniform .

bhuvana89

ans2)

uniform electric field is the one that does not vary from place to place. In terms of the field lines, this means that they are parallel and evenly spaced. Also as field strength = ? (potential gradient), the equipotentials should also be evenly spaced...

well, an example of uniform electric field is the field between plates of a parallel plate capacitor.

rphy

@divalli_oct07 well the magnitude of electric field lines are equal in a uniform Electric Field..dats why its called "uniform".
hmm.. u got to use ur imagination a bit. u must be familiar wid the diagrammatic representation of an electric field. well those electric field lines which are drawn have equal magnitude.

let me know if u have any more doubts. :-)

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iitkgp_bipin

Work done in an electrostatic field need not be zero. Work done when the charge is moved along any equipotential surface is zero. Also work done is zero in a closed loop.

Please post your other query on a new page.

a5hw1n_5

1)u know a charged body in an ext ele fld experiences a force. that force causes work to be done. now apply whatever u hav learnt in work,energy chapter. only if tot didplacement of body in the direction of fore is 0 then the work done is 0.

so if the body moves perpendicular to the electric fld or returns to its original pos then ONLY is the work done in ele fld 0.

2) pot gradient. suppose E is the const ele fld, pot is give by

V=

Edr = Er

which u see is not const, but pot gradient given by V/r= Er/r= E, is a const.

Prakriteesh

Uniform electric field: In such a field the intensity is same at any point inside the field i.e. the electrostatic force experienced by any charge Q will be same irrespective of the location of the charge. Intensity is equal to the negative of the potential gradient ( dV/dR). So, the answer to your second ?ion is potential gradient.

Equipotential surface: It is a surface at which the potential is same at every point, so no change in potential (and hence in potential energy) in moving a charge from one point to another. So no work has to be done to move a charge on such a surface.

Work done in an electric field is zero only under the following circumstances:

1) If it is a round trip i.e. when initial position = final position (it is because electrostatic force is a conservative force)

2) If the surface is equipotential.

3) If the displacement of the charge moved is zero.

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