Can electric dipoles violate Newton's 3rd Law?

In summary, the conversation discusses the possibility of a violation of Newton's third law and conservation of momentum in a scenario where an electric dipole exerts a force on a test charge, but the force on the dipole by the charge cancels to be zero. It is determined that this is not a violation as the forces do not actually cancel in this situation.
  • #1
dipole
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Suppose you have an electric dipole centered at the origin and aligned with the z-axis. If you place a test charge somewhere in the x-y plane, you can show that the force on the dipole by the charge cancels to be zero, yet the dipole still seems to exert a force on the charge...

If this is true, then this is a violation of Newton's third law, and this also means that momentum isn't being conserved (at least not the sum of the momentum of the dipole and of the charge).

Is this situation valid, and is this something which can really happen? If so, where is the momentum going - the electric field somehow?
 
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  • #2
dipole said:
Suppose you have an electric dipole centered at the origin and aligned with the z-axis. If you place a test charge somewhere in the x-y plane, you can show that the force on the dipole by the charge cancels to be zero, yet the dipole still seems to exert a force on the charge...
...

Why do you think forces cancel? As far as I see it, they most certainly do not! Let say dipol is oriented to +z and test charge is positive. Repulsive force z component will be negative, and attractive force by negative part of dipol will have z component also negative, so you don't have cancellation.
 
  • #3
I just realized my error, Newton's 3rd law is safe!
 
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1. Can electric dipoles violate Newton's 3rd Law?

No, electric dipoles cannot violate Newton's 3rd Law. This law states that for every action, there is an equal and opposite reaction. Electric dipoles, which are formed by equal and opposite charges separated by a small distance, follow this law as well. The forces between the charges in a dipole are equal and opposite, ensuring that Newton's 3rd Law is not violated.

2. How do electric dipoles follow Newton's 3rd Law?

Electric dipoles follow Newton's 3rd Law by producing equal and opposite forces between the charges that make up the dipole. These forces are electric in nature and are responsible for the dipole's behavior. The dipole's movement and orientation are determined by the balance of these forces, which always adhere to the principles of Newton's 3rd Law.

3. Can electric dipoles experience net force?

Yes, electric dipoles can experience net force. This can happen when an external electric field is applied to the dipole, causing the charges to experience unequal forces. As a result, the dipole will experience a net force and may rotate or translate in response to this force. However, within the dipole itself, the forces between the charges will always remain equal and opposite, following Newton's 3rd Law.

4. Do electric dipoles only exist in a vacuum?

No, electric dipoles can exist in any medium, including air, water, and solids. In fact, many molecules and materials have permanent electric dipoles that contribute to their properties and behavior. The presence of other particles or molecules in the medium does not affect the dipole's adherence to Newton's 3rd Law.

5. Can electric dipoles be used to violate Newton's 3rd Law?

No, electric dipoles cannot be used to violate Newton's 3rd Law. While the forces between the charges in a dipole can be manipulated, the overall behavior of the dipole is still governed by this fundamental law of physics. Attempts to use electric dipoles to violate this law would ultimately fail.

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