What is Electric Field Strength (E)

Chapter 3.3 Electric Field Strength (E)

Fundamental Electrical and Electronic Principles Third Edition Book
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Fundamental Electrical and Electronic Principles Third Edition Book

  • 78Fundamental Electrical and Electronic Principlesbodies is occupied by the electric fl ux, so there are no ‘ gaps ’ in which a charged particle would not be affected. 4 The lines of force (fl ux) radiate outwards from the surface of a positive charge and terminate at the surface of a negative charge. 5 The lines always leave (or terminate) at right angles to a charged surface. 6 Although the lines drawn on a diagram do not actually exist as such, they are a very convenient way to represent the existence of the electric fi eld. They therefore aid the understanding of its properties and effects. 7 Since force is a vector quantity any line representing it must be arrowed. The convention used here is that the arrows point from the positive to the negative charge. It is evident from Fig. 3.3 that the spacing between the lines of fl ux varies depending upon which part of the fi eld you consider. This means that the fi eld shown is non-uniform. A uniform electric fi eld may be obtained between two parallel charged plates as shown in Fig. 3.4 . QQ Fig. 3.4 Note that the electric fi eld will exist in all of the space surrounding the two plates, but the uniform section exists only in the space between them. Some non-uniformity is shown by the curved lines at the edges (fringing effect). At this stage we are concerned only with the uniform fi eld between the plates. If a positively charged particle was placed between the plates it would experience a force that would cause it to move from the positive to the negative plate. The value of force acting on the particle depends upon what is known as the electric fi eld strength. 3.3 Electric Field Strength (E) This is defi ned as the force per unit charge exerted on a test charge placed inside the electric fi eld. (An outdated name for this property is ‘ electric force ’ ).