(i) Depict magnetic field lines due to two straight, long, parallel conductors carrying steady currents I1 and I2 in the same direction.
(ii) Write the expression for the magnetic field produced by one of the conductor over the other. Deduce an expression for the force per unit length.
(iii) Determine the direction of this force.

Dear Student
(i) Magnetic field lines due to two straight, long, parallel conductors carrying steady currents I1 and I2 in the same direction can be represented as below.


(ii)

Let A 1  and  A 2 B 2  are two infinity long straight conductors.

1  and  I 2  are the current flowing through them and these are  r  distance apart.

Magnetic field induction at a point P on conductor  A B 2  due to current  I 1  passing through  A 1 B 1 is

Force experienced by conductor  of length L kept in magnetic field B and carrying current I is written as 
F =BIL
So, Unit length of  A 2 B 2  will experience a force as

(iii) Conductor  A 1 B 1  also experiences the same amount of force, directed towards  A 2 B 2 . Hence, A 1 B  and  A 2 B 2  attract each other.
Thus
Two linear parallel conductors carrying currents in the same direction attract each other  while in opposite direction repel each other.

Regards

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