**THE FIELD OF AN ELECTRIC DIPOLE**

It is the space around the
dipole in which the electric effect of the dipole can be experienced

*(i)*

*For points on the axis*
Let the point P be at
distance

*r*from the centre of the dipole on the side of the charge*q,*as shown in**Fig. a.**
Then

Where ˆ

**p**is the unit vector along the dipole axis (from –*q*to*q*). Also
The total field at P is

*ii) For points on the equatorial plane*
The magnitudes of the
electric fields due to the two charges +

*q*and –*q*are given by
The directions of

**E**+*q*and**E**–*q*are as shown in**Fig. b**. Clearly, the components normal to the dipole axis cancel away. The components along the dipole axis add up.
The total electric field is
opposite to ˆ

**p**. We have**E**= – (*E*+*q*+*E*–*q*) cosθ ˆ**p.**At large distances (*r*>>*a*), this reduces to*q*and

*a*separately; it depends on the product

*qa*. This suggests the definition of dipole moment.

The

*dipole moment vector***p**of an electric dipole is defined by**p**=*q*× 2*a*ˆ**p**that is, it is a vector whose magnitude is charge*q*times the separation 2*a*(between the pair of charges*q*, –*q*) and the direction is along the line from –*q*to*q*.
In terms of

**p**, the electric field of dipole at large distances takes simple forms:
Notice the important point
that the dipole field at large distances falls off not as 1/

*r*2 but as1/*r*3. Further, the magnitude and the direction of the dipole field depend not only on the distance*r*but also on the*angle*between the position vector**r**and the dipole moment**p**.
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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?

Q5: Is mass of body affected on charging?

Q6: What is the polarity of charge?

**Answer these questions in comment box and help your friends**

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