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Emf Induced in a Rotating Coil placed in a Magnetic Field | Emf Induced | Magnetic Circuit

EMF Induced in a Rotating Coil Placed in a Magnetic Field :

 👉Consider a coil AB placed on the outer periphery of a soft iron solid cylindrical rotor. The stator poles carry the exciting coils. When current flows through exciting coils flux is set up as shown in Fig. 1. The rotor is rotating in the clockwise direction at a constant angular velocity of Z radians/sec. The direction of the linear velocity (perpendicular to the plane of the coil) acting on conductor A is shown in Fig.1 which makes an angle T with the direction of the field. The component of velocity perpendicular to the field is vp = v sin T.


                                                        FIG: 1

The emf induced in conductor A, e = Blv sin T

Where,
B = flux density in the rotor in Tesla
l = effective length of the conductor in meter

FIG: 2

As the coil has two conductors only, emf induced in the coil at this instant,
                                          e = 2 Blv sin T

If a coil has N number of turns then, emf induced in coil = 2NBlv sin T
If the angle between the plane of the coil and the direction of the magnetic field is D, then the component of velocity is perpendicular to the field vU = v cos D (see Fig below).

 The emf induced in the coil, e = 2 N Blv cos D

The direction of induced emf in conductors A and B can be determined by applying Fleming’s Right-Hand Rule or Lenz’s Law. By applying Fleming’s Right-Hand Rule to conductor A, which is moving downward, the induced emf is out of the plane of paper [ ], whereas conductor B is moving upward and the induced emf is into the plane of paper [† ].

 According to Lenz’s Law, we can say that when the coil is rotating in a clockwise direction the flux linkages are decreasing [see Fig. 3(A)]. Thus the emf induced in the coil would have the direction such that the magnetic flux produced by its current tends to oppose the decreasing flux linkages i.e., the coil will set up the field which will increase the flux linking with the coil [see Fig. 3 (B)].

FIG : 3

The magnitude of induced emf depends upon the sine of angle T. The emf induced in the coil at positions (a), (e), and (i) in Fig. below is zero and at positions (c) and (g) it is maximum. The variation of emf concerning angle T is shown graphically in Fig. below

FIG: 4


The above arguments regarding the magnitude and direction of the emf induced are equally applicable if the main magnetic field is rotating and the coil is kept stationary.

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