## Thursday, November 22, 2012

### Electric Field Lines

An electric field line is, in general, a curve drawn in such a way that the tangent to it at each point is in the direction of the net field at that point.

An arrow on the curve is obviously necessary to specify the direction of electric field from the two possible directions indicated by a tangent to the curve. A field line is a space curve, i.e., a curve in three dimensions.

The field lines follow some important general properties:

(i)                Field lines start from positive charges and end at negative charges. If there is a single charge, they may start or end at infinity.

(ii)               In a charge-free region, electric field lines can be taken to be continuous curves without any breaks.

(iii) Two field lines can never cross each other. (If they did, the field at the point of intersection will not have a unique direction, which is absurd.)

(iv) Electrostatic field lines do not form any closed loops. This follows from the conservative nature of electric field

(v) The electric field lines are always normal.

Magnitude of electric field is represented by the density of field lines.
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Some of these questions which may be asked in your Board Examination 2012-2013

Q1: what are the characteristic of charges acquired by the objects on rubbing against each other?

Q2: Who suggested first that there are two kinds of charges?

Q3: How can you show that there are two types of charges?

Q4: An ebonite rod is rubbed with the fur or wool. What type of charges do they acquire?

Q5Is mass of body affected on charging?

Q6: What is the polarity of charge?