Sign convention for work.

  • Thread starter Calpalned
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  • #1
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Main Question or Discussion Point

If the work done by an electric field is N, then the work done by me will be negative N? Perhaps this applies if I move a charge against the field lines, but what if I move in the same direction?
 

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  • #2
Chandra Prayaga
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I presume the context here is that you are moving an object with negligible kinetic energy so that the net work done by the field plus your hand is zero. That is when the force bu you is opposite to the force by the electric field, and the work done by you will be the negative of the work done by the electric field. If you move the object in the same direction as the electric field is moving it, then certainly, the total work is not zero, the kinetic energy will keep increasing. Nothing prevents you from helping the electric field.
 
  • #3
andrewkirk
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If you move in the same direction then either:

1. You are pulling the particle against the field, hence slowing it down so that its final KE is less than it would have been if it had been freely moving under the force of the field alone.
2. You are pulling the particle with the field, hence accelerating it even more than the field is so that its final KE is more than it would have been if it had been freely moving under the force of the field alone.

In both cases, the work you have done is equal to the final KE of the particle minus what the final KE would have been if you had not interfered with the particle.
 

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