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Old Jul 14th 2009, 06:29 PM   #1
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Fields and electricity

1) Directions of the fields are indicated on field lines. Why are no directions indicated on equipotential lines?

2) Explain how a gravitational field might be mapped.

3) For a series circuit, what is the terminal voltage of a battery or power supply equal to in terms of the potential differences or voltage drops across circuit components?
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Old Jul 14th 2009, 10:24 PM   #2
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1) Directions of the fields are indicated on field lines. Why are no directions indicated on equipotential lines?


If a field is shown for say a +ve charge, then the lines are shown as diverging from it. In case of say a parallel plate capacitor, or a charge at infinity, The lines are shown parallel but with direction. I dont understand what you mean by equipotential lines. If you are considering 2 points at the same potential, then there is no field from one to the other.


2) Explain how a gravitational field might be mapped.

The same as that for a -ve charge with the lines pointing towards the mass.

3) For a series circuit, what is the terminal voltage of a battery or power supply equal to in terms of the potential differences or voltage drops across circuit components?

The terminal voltage is equal to the sum of the potential differences or voltage drops across circuit components. If the cell has an internal resistance, the terminal voltage will be the cell voltage minus the voltage drop across this internal resistance at the rated current.
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Old Jul 16th 2009, 06:06 PM   #3
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Originally Posted by physicsquest View Post
1) Directions of the fields are indicated on field lines. Why are no directions indicated on equipotential lines?


If a field is shown for say a +ve charge, then the lines are shown as diverging from it. In case of say a parallel plate capacitor, or a charge at infinity, The lines are shown parallel but with direction. I dont understand what you mean by equipotential lines. If you are considering 2 points at the same potential, then there is no field from one to the other.
An equipotential line is a curve on which a charged particle has the same value of potential energy. It can also be described as a curve on which the electric potential has the same value.

Picture a point charge lying in a plane. Let the value of the charge be +q. The the electric potential at a distance r has the value V = q/r (in esu units). The curve defined by r = constant is a circle. That circle is called a line of equipotential. In three dimensions there is an equipotential surface.

See - Equipotential Lines

The reason there is no direction is because there is no direction associated with a scalar quantity.
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