Electrical Engineering ⇒ Topic : Electric Field

Electric Field

The region surrounding a charged body is always under stress and strain because of the electrostatic charge. If a small charge is placed in this region, it will experience a force according to Coulomb's laws. This stressed region around a charged body is called electric field. Theoretically, electric field due to a charge extends upto infinity but its effect practically dies away very quickly as the distance from the charge increases.

The space (or field) in which a charge experiences a force is called an electric field or electrostatic field.

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                                                                      figure (a)

The electric field around a charged body is represented by imaginary lines, called electric lines of *force. By convention, the direction of these lines of force at any point is the direction along which a unit positive charge (i.e., positive charge of 1C) placed at that point would move or tend to move.The unit positive charge is sometimes called a test charge because it is used as an indicator to find the direction of electric field. Following this convention, it is clear that electric lines of force would always originate from a positive charge and end on a negative charge. The electric lines of force leave or enter the charged surface **normally.

Fig. (a) shows typical field distribution. Fig. A (i) shows electric field due to an isolated positively charged sphere. A unit positive charge placed near it will experience a force directed radially away from the sphere. Therefore, the direction of electric field will be radially outward as shown in Fig. A (i). For the negatively charged sphere [See Fig. A (ii)], the force acting on the unit positive charge would be directed radially towards the sphere. Fig. A (iii) shows the electric field between a positive charge and a negative charge while Fig. A (iv) shows electric field between two similarly charged (i. e. + vely charged) bodies

Electric Field or Electric Flux Lines (w)

Consider a point charge q as shown in Fig. 1 (a). At any point, at distance r from q, the direction of E is radially outwards as shown in the figure. On the other hand, if the charge is negative, the E vectors act in the direction of the charge as shown in Fig. 1 (b). It can be seen from these figures that something emanates from a positive charge q [Fig. 1 (a)], while something terminates on the negative charge q [Fig. 1 (b)]. These patterns of vectors representing the electric field intensity at any point are called electric flux lines or electric field lines. In the RMKS system of units, the amount of electric flux that emanates from a positive charge is numerically equal to q. The above figures indicate that electric flux lines start from a positive charge and end on a negative charge. This is shown in Fig. 2 (a). Electric field due to like charges is shown in Fig. 2 (b).The electric field intensity is zero at N mid-way between the charges. Such points are known as singular points the electric field

                                                                       figure (1) Electric field due to isolated charges

                                figure (2) Electric field lines around two unlike charges (a) and around two like charges (b)