# Electric field work physics problem

• Gear300
In summary, when a charged particle passes through an electric field, it is accelerated towards one of the plates by the field's natural direction towards lower potential energy. The work done by the conservative force is positive and can be calculated using the formula W = -q*deltaV. The potential difference can also be solved for using W= -Vq, which is the amount of work needed to move the test charge from one point to another. However, in a non-uniform electric field, the potential does not depend on the test charge, but the electric potential energy does. If a negative charge is brought towards lower electric potentials, the work done by the conservative force is negative. This exchange of signs applies to all charges and potentials.
Gear300
For point charges within an electric field, the natural direction a point charge takes in respect to a field would be towards lower potential energy, whereas the work done by the conservative force should be positive. So then, by W = -q*deltaV, do they refer to the magnitude of the test charge q? If deltaV was negative, it indicates that positive work was done...but if the charge is negative, the work becomes negative.

I'm not sure if I'm answering your question but W= -qEd which is equivalent to the change in potential energy in a UNIFORM field only.

The potential difference can be solved for using W= -Vq this is the amount of work it takes to move the test charge from a point a to point b say in between two plates

The electric potential V in an non uniform field does not depend on the test charge and its formula is then V=KQ/R

Electric potential energy on the other hand is defined as PE= Vq and does depend on the magnitude of the test charge and its sign.

In sum remember that Electric Potential does not depend on q; but that Electric Potential Energy (PE) does depend on q.

I see...but then in that sense -deltaU = W done by conservative force and deltaU/q = deltaV. That implies that -deltaV*q = W done by conservative force. For any particle in respect to a conservative force, its movement is towards less potential energy, which should also result in a decrease in electric potential (making deltaV negative). If W = -q*deltaV, then doesn't that imply that if an electron was naturally moving due to an electric force, W would be negative, whereas conceptually the actual work done by the conservative force should be positive?

An electron moves towards a higher potential. Electric potential is defined as the potential energy of a positive test charge.

wait a minute...you're right. So if deltaV is negative and q is negative, deltaU is positive...which means work was done against the conservative force, whereas, the conservative force does negative work in this case. So can we make this generalization?: If a negative charge is brought towards lower electric potentials, then the work done by the conservative force is negative.

Gear300 said:
wait a minute...you're right. So if deltaV is negative and q is negative, deltaU is positive...which means work was done against the conservative force, whereas, the conservative force does negative work in this case. So can we make this generalization?: If a negative charge is brought towards lower electric potentials, then the work done by the conservative force is negative.

yes. If you exchange the sign of all charges and potentials, all the forces and energies should come out the same.

Work in an electric field

When a charged particle passes between two parallel plates connected to a voltage source, the particle is accelerated toward one of the plates by the field. Assuming that the particle continues on its way without contacting either plate, how is the work done on the particle "paid back"? Is there a mechanism that reduces the field strength E by delta E that requires a current through the voltage source to restore the field to E? If so, what is the mechanism? If not, how is the work accounted for?

thanks-

Eric

If The particle picks up speed between the plates, it must have started at a higher (or lower for a negative particle) potential. If the particle is shot between the plates from far away (where the potential is very close to 0) and then flies off again to a far away point, the field can't have done any work on it.

Could you say that any particle that is accelerated in an electric field must have started from a higher potential, so that no work may be done by an electric field on any particle that is accelerated in the field?

## What is an electric field?

An electric field is a physical quantity that describes the force experienced by a charged particle in the presence of other charged particles. It is a vector quantity, meaning it has both magnitude and direction.

## How is electric field measured?

Electric field is measured in units of newtons per coulomb (N/C) or volts per meter (V/m). This can be measured using instruments such as an electroscope or a voltmeter.

## What is electric field work?

Electric field work is the amount of work required to move a charged particle from one point to another within an electric field. This work is equal to the product of the electric field strength and the distance moved by the particle.

## How is electric field work calculated?

The formula for calculating electric field work is W = qEd, where q is the charge of the particle, E is the electric field strength, and d is the distance moved by the particle. The unit of electric field work is joules (J).

## Can electric field work be negative?

Yes, electric field work can be negative if the force on the particle is in the opposite direction of the displacement. This can happen if the particle moves towards a region of lower electric potential.

• Introductory Physics Homework Help
Replies
22
Views
2K
• Introductory Physics Homework Help
Replies
9
Views
428
• Introductory Physics Homework Help
Replies
7
Views
1K
• Introductory Physics Homework Help
Replies
6
Views
1K
• Introductory Physics Homework Help
Replies
2
Views
655
• Introductory Physics Homework Help
Replies
23
Views
864
• Introductory Physics Homework Help
Replies
10
Views
294
• Introductory Physics Homework Help
Replies
10
Views
470
• Introductory Physics Homework Help
Replies
2
Views
1K
• Introductory Physics Homework Help
Replies
14
Views
750