Flux linkage is the term used in mutual inductance as a measure of the linkage of magnetic flux lines of one conducting coil to another. The concept of flux linkage is based on Faraday's observation that there is an electro-motive force (EMF) induced in a conductor when it is placed in a magnetic field. The phenomenon of flux linkage is used in important electrical devices like the transformer and generator.
Measurement of flux linkage
The flux linkage is measured in weber-turns and is calculated as a product of magnetic flux (Ф) and the number of turns in the coil that are linked by the magnetic flux. The magnetic flux (Ф) is product of the magnetic flux density (measured in Tesla and denoted by B) and the area when the field is projected at right angles to the area.
In order to calculate the flux linkage, the following relation holds good:
Flux linkage=Number of turns of coil(N) × Magnetic field strength (B) × area(A) Thus, it is possible to denote flux linkage by NФ or NBA.
Altering flux linkage
It is possible to alter the flux linkage by the following two methods:
- By altering the strength of the magnetic field
- The area of coil being linked can be altered from its ideal position of 90° to the magnetic field. This is possible by moving the conducting coil through which magnetic flux lines cut. If the coil is turned by an angle θ to the magnetic field, then the new flux linkage is given by NBAsinθ.
Electromagnetic induction by flux linkage
With the help of flux linkage, it is possible to induce a voltage and current in a conducting coil. This is done by moving the coil in a magnetic field. This is a converse of the phenomenon that when a current is passed in a wire placed in a magnetic field, the conductor experiences a force, causing it to move.
The induced voltage, called the EMF, in a conducting coil is indicated by a suitable galvanometer.
Voltage as a result of flux linkage can be altered by using a second conducting coil instead of a magnet, giving rise to the concept of mutual inductance. This phenomenon is used in the transformer.