Currents in the Same Direction Attract Each Other
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When two parallel current carrying conductors are close together, they exert force on each other. It is because one current carrying conductor is placed in the magnetic field of the other. If currents are in the same direction, the conductors attract each other, otherwise they repel. The direction of force can be checked using Fleming's left hand rule. One can see below that these forces are always equal and opposite on the two wires, even when the currents are not equal.
Consider two conductors parallel to each other separated by a distance r. The magnetic field induction at P on CD due to current I
1 is
This conductor experiences a force F
2 and points towards left according to Fleming's left hand rule. Now,
The force per unit length on each of the conductor is
Since the directions are towards each other, the two conductors attract each other.
Definition of Ampere
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If I1 = I2 = 1
r = 1m
then,
F = 2x10
-7 N/m
One ampere is that much current which when flowing through each of the two parallel conductors of length 1m and separated by 1m in vacuum experiences an attractive or repulsive force of 2 x 10-7N per metre of their length.
