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We use electric field lines to visualize and analyze electric fields (the lines are a pictorial tool, not a physical entity in themselves). The properties of electric field lines for any charge distribution can be summarized as follows:

  1. Field lines must begin on positive charges and terminate on negative charges, or at infinity in the hypothetical case of isolated charges.
  2. The number of field lines leaving a positive charge or entering a negative charge is proportional to the magnitude of the charge.
  3. The strength of the field is proportional to the closeness of the field lines—more precisely, it is proportional to the number of lines per unit area perpendicular to the lines.
  4. The direction of the electric field is tangent to the field line at any point in space.
  5. Field lines can never cross.

The last property means that the field is unique at any point. The field line represents the direction of the field; so if they crossed, the field would have two directions at that location (an impossibility if the field is unique).

Phet explorations: charges and fields

Move point charges around on the playing field and then view the electric field, voltages, equipotential lines, and more. It's colorful, it's dynamic, it's free.

Charges and Fields

Section summary

  • Drawings of electric field lines are useful visual tools. The properties of electric field lines for any charge distribution are that:
  • Field lines must begin on positive charges and terminate on negative charges, or at infinity in the hypothetical case of isolated charges.
  • The number of field lines leaving a positive charge or entering a negative charge is proportional to the magnitude of the charge.
  • The strength of the field is proportional to the closeness of the field lines—more precisely, it is proportional to the number of lines per unit area perpendicular to the lines.
  • The direction of the electric field is tangent to the field line at any point in space.
  • Field lines can never cross.

Conceptual questions

Compare and contrast the Coulomb force field and the electric field. To do this, make a list of five properties for the Coulomb force field analogous to the five properties listed for electric field lines. Compare each item in your list of Coulomb force field properties with those of the electric field—are they the same or different? (For example, electric field lines cannot cross. Is the same true for Coulomb field lines?)

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[link] shows an electric field extending over three regions, labeled I, II, and III. Answer the following questions. (a) Are there any isolated charges? If so, in what region and what are their signs? (b) Where is the field strongest? (c) Where is it weakest? (d) Where is the field the most uniform?

Five field lines represented by long arrows horizontally from left to right are shown. Two arrows diverge from other three, one arrow runs straight toward right and two arrows end abruptly.
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Problem exercises

(a) Sketch the electric field lines near a point charge + q . (b) Do the same for a point charge –3.00 q .

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Sketch the electric field lines a long distance from the charge distributions shown in [link] (a) and (b)

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[link] shows the electric field lines near two charges q 1 size 12{q rSub { size 8{1} } } {} and q 2 size 12{q rSub { size 8{2} } } {} . What is the ratio of their magnitudes? (b) Sketch the electric field lines a long distance from the charges shown in the figure.

Field lines between a positive and a negative charge represented by curved lines is shown
The electric field near two charges.
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Sketch the electric field lines in the vicinity of two opposite charges, where the negative charge is three times greater in magnitude than the positive. (See [link] for a similar situation).

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Questions & Answers

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Specific heat capacity is the amount of heat required to raise the temperature of one (Kg) of a substance through one Kelvin
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formula for measuring Joules
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Boyles law states that the volume of a fixed amount of a gas is inversely proportional to the pressure acting on in provided that the temperature is constant.that is V=k(1/p) or V=k/p
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Force is any quantity or a change that produces motion on an object body.
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A force is a push or a pull that has the tendency of changing a body's uniform state of rest or uniform state of motion in a straight line.
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f=Gm/d²
FADILAT
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electro magnetic force
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Electromotive force (emf) is a measurement of the energy that causes current to flow through a circuit.
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Continue - > tritium (gas, netrogen, cloud, lamp span, lamp light, cool)
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Practice Key Terms 4

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Source:  OpenStax, College physics. OpenStax CNX. Jul 27, 2015 Download for free at http://legacy.cnx.org/content/col11406/1.9
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