Electric Dipole | Definition, Examples, Diagrams

A small electric dipole having dipole moment

p

is placed along X-axis, as shown in the figure. A semi-infinite uniformly charged di-electric thin rod  placed along x axis, with one end coinciding with origin. If linear charge density rod is

+

λ

and distance of dipole from rod is

a

, then calculate the electric force acting on dipole.
Electric field at A due to dipole,  

E

A

=

r

3

2

K

P

           where

K

=

4

π

ϵ

o

1

E

A

=

(

x

+

a

)

3

2

K

P

Force at A due to dipole,  

F

A

=

q

E

A

=

(

λ

d

x

)

×

(

x

+

a

)

3

2

K

P

F

A

=

(

x

+

a

)

3

2

λ

K

P

d

x

Total force exerted due to dipole on the rod,    

F

D

=

0

(

x

+

a

)

3

2

λ

K

P

d

x

F

D

=

2

λ

K

P

×

2

(

x

+

a

)

2

1

0

  

F

D

=

a

2

λ

K

P

Now force exerted by rod on dipole is equal and opposite to

F

D

 (Newton’s law)

F

R

=

F

D

=

4

π

ϵ

o

a

2

λ

P