Briefly explain the change in flux due to rate of change of area?

Magnetic flux is defined as the total number of magnetic field lines through a given coil or area. It is the common component of the magnetic field that passes through the coil. Magnetic flux is denoted by ΦB where B is a magnetic field and its unit is Weber (Wb). The magnetic flux value depends on the magnetic field direction and it is a vector quantity.

Magnetic flux formula is given by:

Φ = BA cosƟ


  • ΦB is the magnetic flux.
  • B is the magnetic field
  • A is the area
  • θ the angle at which the field lines pass through the given surface area

Rate of change of magnetic flux due to rate of change of area

According to Faraday’s second law of electromagnetic induction, we know that the induced emf in a coil is equal to the rate of change of flux linkage. Therefore,

E =- dφ/dt where φ = B.A where A is a very small area.

So E = – B. d A / dt – A. d B / dt

The first term is called motional emf because it is connected with area change, i.e., movement of the loop periphery. The induced electric field E = v x B originates from the accumulation of free electrons at one end of the conductor due to Lorentz magnetic force F = q v x B.

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