Dynamically Induced e.m.f

Dynamically Induced e.m.f Points : Dynamically Induced e.m.f In the three conductors A, 8 and C are shown in cross-section, moving in a field (flux density B) in the directions shown by the arrows. Conductor A is moving in a direction perpendicular to its length and perpendicular to the magnetic lines of force and therefore cuts the lines of force and an e.m.f. is induced in the conductor. If the conductor moves by a distance dx in a time dt, the area swept by the conductor equals / dx where I is the length of the conductor.
It illustrates the Lenz’s law. It is found that as the conductor is moved up, the centre zero galvanometer deflects to the left which indicates that the polarity of the induced e.m.f and the direction of the current are as shown. The induced current sets up a flux in clockwise direction. The effect of this flux is to strengthen the magnetic field above the conductor and to weaken the field below the conductor. This creates a force on the conductor in the downward direction. Thus .the magnetic flux set up by the induced current tends to oppose the motion of the conductor. To account for the fact that the induced e.m.f. opposes the change in flux, a negative sign is sometimes added. However if it is kept in mind that the direction of induced e.m.f. is always such as to oppose the change in flux, there is no need of the negative sign.