Whenever the magnetic flux linked with a coil (or a closed circuit) changes with time, an emf and a current are induced in the circuit. This phenomenon first observed by Faraday is called electromagnetic induction.
Magnetic flux associated with any area is given by the expression
Here B→is the magnetic field and ds→ is area element. Area is taken as a vector quantity and its direction is perpendicular to surface
Flux associated with plane coil having N turns in a uniform magnetic field B→ is equal to
=> N( B→. A→)
=> φB = NBA cosθ
Here N is the number of turns in the loop
B = magnetic field strength
A = area of the loop
θ = angle between area vector and magnetic field.