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The B-field induced by this return current opposes the applied B-field, tending to decrease the flux through that side of the circuit, opposing the increase in flux due to rotation. On the near side of the figure, the return current flows from the rotating arm through the near side of the rim to the bottom brush.
The magnetic Lorentz force v × B drives a current along the conducting radius to the conducting rim, and from there the circuit completes through the lower brush and the axle supporting the disc. This device generates an emf and a current, although the shape of the "circuit" is constant and thus the flux through the circuit does not change ...
This induced voltage created by the changing current has the effect of opposing the change in current. This is stated by Lenz's law , and the voltage is called back EMF . Inductance is defined as the ratio of the induced voltage to the rate of change of current causing it. [ 1 ]
where is back EMF, is the constant, is the flux, and is the angular velocity. By Lenz's law, a running motor generates a back-EMF proportional to the speed. Once the motor's rotational velocity is such that the back-EMF is equal to the battery voltage (also called DC line voltage), the motor reaches its limit speed.
The light-induced charge separation eventually creates a forward current through the cell's internal resistance in the direction opposite the light-induced current . In addition, the induced voltage tends to forward bias the junction, which at high enough voltages will cause a recombination current I D {\displaystyle I_{D}} in the diode ...
In electromagnetism, an eddy current (also called Foucault's current) is a loop of electric current induced within conductors by a changing magnetic field in the conductor according to Faraday's law of induction or by the relative motion of a conductor in a magnetic field. Eddy currents flow in closed loops within conductors, in planes ...
That is, the back-EMF is also due to inductance and Faraday's law, but occurs even when the motor current is not changing, and arises from the geometric considerations of an armature spinning in a magnetic field. This voltage is in series with and opposes the original applied voltage and is called "back-electromotive force" (by Lenz's law).
This means that the direction of the back EMF of an induced field opposes the changing current that is its cause. D.J. Griffiths summarized it as follows: Nature abhors a change in flux. [7] If a change in the magnetic field of current i 1 induces another electric current, i 2, the direction of i 2 is opposite that of the change in i 1.