The force field carries the force to another object called a test object some distance away. A field is a way of conceptualizing and mapping the force that surrounds any object and acts on another object at a distance without apparent physical connection. For example, the gravitational field surrounding the earth and all other masses represents the gravitational force that would be experienced if another mass were placed at a given point within the field.
In the same way, the Coulomb force field surrounding any charge extends throughout space. Both the magnitude and direction of the Coulomb force field depend on Q and the test charge q. Figure 1. The Coulomb force field due to a positive charge Q is shown acting on two different charges. Both charges are the same distance from Q. The Coulomb force field is thus not unique at any point in space, because it depends on the test charges q 1 and q 2 as well as the charge Q.
To simplify things, we would prefer to have a field that depends only on Q and not on the test charge q. The electric field is defined in such a manner that it represents only the charge creating it and is unique at every point in space. Specifically, the electric field E is defined to be the ratio of the Coulomb force to the test charge:. It is understood that E is in the same direction as F. It is also assumed that q is so small that it does not alter the charge distribution creating the electric field.
Consider the electric field due to a point charge Q. Thus the magnitude of the electric field, E , for a point charge is.
The electric field is thus seen to depend only on the charge Q and the distance r ; it is completely independent of the test charge q. The magnitude of the field and the density of the field lines scale as the inverse of the distance squared. The field lines of an electric dipole , i.
Polar molecules do not have a net charge, but the centers of the positive and negative charge do not coincide. Such molecules produce a dipole field and interact via the electrostatic force with their neighbors. The field lines of two positive charges of equal magnitude separated by a distance d. Every water molecule H 2 O consists of one oxygen atom and two hydrogen atoms. A water molecule has no net charge because the number of positively charged protons equals the number of negatively charged electrons in each atom.
In the water molecule, each hydrogen atom is bound to the oxygen atom by a covalent bond. The hydrogen atom and the oxygen atom share an electron, which has a slightly higher probability to be closer to the oxygen atom than to the hydrogen atom. This results in a polar molecule , in which the oxygen "side" of the molecule has a slight negative charge, while the hydrogen "sides" have a slight positive charge.
Because water is a polar molecule it dissolves many inorganic and organic materials. Organisms can build macromolecules to attract or repel water as needed simply by varying the charge on side chains. The figure on the right shows the electric field lines for a system of two point charges. The field of an infinite planar charge distribution is uniform. It does not decrease with distance. Of course, there are no infinite sheets of charge. The most important application of the above result is the superposition of the fields from two planar charge distributions which are separated by some distance d.
The fields add to yield a uniform field between the planes, but they precisely cancel outside the planes to give zero net field outside. Between the planes the field points from the positive towards the negative plane. This is the common configuration of a parallel plate capacitor. Please watch this video clip that helps you "see" the electric field!
Discuss this with your fellow students in the discussion forum! Review the rules for drawing electric field lines. It is easy to become confused by the mathematics of electric field strength. It is important to bear in mind that there are always two charges involved in any electrical interaction. In this case, the charges are Q and q. Big Q represents the source charge which creates the electric field. Little q represents the test charge which is used to measure the strength of the electric field at a given location surrounding the source charge.
Give considerable attention to the charge quantity - Q or q - being used in each equation. The electric field strength E at any location surrounding a source charge can be determined by measuring the force F exerted upon some test charge q which is placed at that location. The standard metric units of a quantity can be understood by thinking about its formula. Electric field strength is the ratio of force to charge see Formula Fix section above.
So the units on electric field strength are units of force divided by units of charge. The standard metric unit of force is the Newton; the standard metric unit of charge is the Coulomb. What units are used to express electric field strength?
A 4 microCoulomb charge exerts a force of 9. Note: Your actual True-False statement is picked at random from a collection of choices and may vary from the one listed here.
Is electric field a scalar or a vector quantity? How can one determine the direction of an electric field?
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