Electric Field
There is a charge of force around the medium, acts on a negative or positive charge when placed in the medium. If the charge is a huge , then it may create such a large stresses and causes the electrical damage to the medium, followed by the passage of an arc discharge.
The place in which the stresses leaves or in which the forces act, is called an electric field or electrostatic field.
These stresses are represented by imaginary lines of forces. The direction of the lines of forces at any points is the direction along with a unit positive charge placed at that point would move if free to do so. According to Faraday the electric field should be imagined to be divided into tubes of force consisting of fixed number of lines of force.
He considered these tubes having elasticity and the property of contracting longitudinally the repelling laterally. Fundamentals of this theory it becomes easy to explain
(i) Why unlike charges attract each other and try to come nearer to each other.
(ii) Why same charges repel each other and try to go from each other.
However, it is more common to use the term lines of force. These lines are supposed to emanate from a positive charge and end on a negative charge. These lines always enter or leave a conducting surface normally.
Electrostatic induction.
It is a common practice when a charge body comes near uncharged body, it acquires some charge. This phenomenon of an uncharged body getting charge merely by the nearness of a charge body is called as induction. When a positively charged body A is placed close to the perfectly insulated uncharged body B, It is found that the end of B nearer to A gets negatively charged whereas further end becomes positively charged.
The positive and negative charge of B are known as induced charges. However the positive charge on the further end of B is called fee charge. In other figure when body B is earthed by a wire, the positive charge flows to earth leaving negative charge behind. If next A is removed, then this negative charge will also go to earth, leaving B uncharged. So the results are
(a) A positive charge induces a negative charge and vice-versa.
(b) Each of the induced charges is equal to the inducing charge.
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