When two parallel current carrying conductors are close enough they exert force on each other. This can be realized by doing the following activity
Through the above activity we can realize that the conductors attract each other when the current in them are parallel and repels when the current is antiparallel. In the above experiment each conductor is situated in the magnetic field due to the other. This is the reason of the force of interaction between them. Our next aim is to obtain a general expression of force acting between two parallel current carrying conductors.
Consider two very long conductors carrying currents I1 and I2 arranged parallel at a distance r apart. The magnetic field due to the first conductor at a distance r away from it is
B=muzero/4pix 2I1/r
The second conductor carrying current is placed in this magnetic field. Hence the force experienced by a length l of it is BI2l.
The force experienced per unit length is given by F=BI2=muzero/4pix 2I1I2/r
In SI system the unit of electric current intensity is defined using the force experienced by the parallel conductors carrying current. The definition is as follows:
One ampere is defined as that current which when flowing through each of two parallel conductors of negligible cross section and infinite length placed 1m apart in free space would impart a force of 2x10-7 N/m on each other.
Group Activity
Arrange two thin aluminium foils (10 cm x 10 cm) on two pencils with the help of crocodile pins. Connect a dc source (9V) to the foils such that the direction of current is same in both the foils. Note down your observation. Now reconnect the dc source such that the direction of current in the foils are in the opposite direction. Note down the new observation also. Now try to find the reason for your observation in a group discussion.
Through the above activity we can realize that the conductors attract each other when the current in them are parallel and repels when the current is antiparallel. In the above experiment each conductor is situated in the magnetic field due to the other. This is the reason of the force of interaction between them. Our next aim is to obtain a general expression of force acting between two parallel current carrying conductors.
Consider two very long conductors carrying currents I1 and I2 arranged parallel at a distance r apart. The magnetic field due to the first conductor at a distance r away from it is
B=muzero/4pix 2I1/r
The second conductor carrying current is placed in this magnetic field. Hence the force experienced by a length l of it is BI2l.
The force experienced per unit length is given by F=BI2=muzero/4pix 2I1I2/r
In SI system the unit of electric current intensity is defined using the force experienced by the parallel conductors carrying current. The definition is as follows:
One ampere is defined as that current which when flowing through each of two parallel conductors of negligible cross section and infinite length placed 1m apart in free space would impart a force of 2x10-7 N/m on each other.
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