Why don't the electric field lines represent the paths of particles?? Watch

>>MMM<<
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My book states 'Electric Field Lines Are Not Paths of Particles! Electric field lines represent the field at various locations. Except in very special cases,they do not represent the path of a charged particle moving in an electric field.'

Can someone please care to explain this to me? Im very confused? Aren't the electric field lines supposed to show the direction of the force on a small positive charge? :confused:
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RoyalBlue7
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Yes it shows the direction of the electrical force on a positive charged particle.

The book is saying, I reckon, that it shouldn't be confused with the path the positive particle takes. For example if a positive charged particles enters a uniform electric field with a certain velocity it doesn't stop, turn and go along the electric field line.

But I've always wondered if a positive charged particle is placed at REST would it follow the electric field line? :erm:

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uberteknik
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(Original post by RoyalBlue7)
But I've always wondered if a positive charged particle is placed at REST would it follow the electric field line? :erm:

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Yes it would as long as the field lines remain straight lines and do not deviate:

Don't forget that force is a vector quantity, it has both magnitude and direction. A stationary particle will accelerate in the same direction as the applied force - basic Newtons laws

However, if the particle is already moving wrt the electric field, then the particle already has momentum (mass x velocity) and the trajectory of the particle will therefore be the vector product of the two. This is exactly analogous to the way gravity affects the trajectory of an object moving relative to a gravitational field. Let go of a ball held stationary above the ground and it accelerates straight down along the gravitational field lines. Throw the ball parallel to the ground and what happens to it's trajectory? Ballistics in other words.

Don't forget that if the electric field is not uniform, then the force on the particle is changing as it moves through the field and so the trajectory must also change.
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Stonebridge
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OP. If a charge entered a uniform electric field that was at right angles to its direction of motion (like in an oscilloscope) are you expecting it to suddenly do a sharp right angle turn and move along the lines of force? Common sense says NO.
It would actually move in a smooth curved parabolic path.
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Martin Hogbin
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A charge particle will not follow electric field lines for two reasons.1) All real charged particles have mass. This means that, although the electric force on a charged particle will be along the the field lines, its momentum will make it tend to continue in a straight line. 2) Once the particle gets moving it will also be subject to a magnetic force. The vector sum of the electric and magnetic forces is known as the Lorentz force.
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Martin Hogbin
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Ignore my reason 2 above. I had a sudden rush of blood to the brain. The magnetic force on the particle only applies if there is a magnetic field present. Reason 1 is fine though.
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