Motional Emf

Claimed --Jli639 (talk) 14:50, 5 November 2015 (EST)

Motional emf is emf caused by motion in a magnetic field, leading to polarization.

The Main Idea

A metal bar moving through a magnetic field will polarize as a result of magnetic force, and the resulting charge separation, maintained by the magnetic force, is reminiscent of a battery. The polarized bar can then be used to generate an electric current in a circuit.

Additionally, as a result of the polarization, an electric field is also generated.

Polarization and Steady State

Polarization occurs due to the shift of the mobile electron sea in one direction. Eventually, the shifting will stop; enough electrons will shift in a particular direction so that the electric force, in the opposite direction, balances out the magnetic force (qvB = qE). Consequently, in the steady state, E = vB and there is no net force on the bar, so the bar does not require any additional force to keep it moving at a constant velocity.

In the steady state, a nonzero E-field exists inside the metal bar; however, if the bar is not connected in a circuit, there is no current. This is because the electric force is balanced with the magnetic force, resulting in zero net force on the mobile electrons. The potential difference across the metal bar is then the product of the electric field and the length of the bar, or vBL.

Driving Current

If the metal bar is used to form a circuit, where the bar is slid along on two frictionless metal rails that are also connected, then the charge separation in the bar mimics a battery and can drive a current.

A Mathematical Model

What are the mathematical equations that allow us to model this topic. For example [math]\displaystyle{ {\frac{d\vec{p}}{dt}}_{system} = \vec{F}_{net} }[/math] where p is the momentum of the system and F is the net force from the surroundings.

A Computational Model

How do we visualize or predict using this topic. Consider embedding some vpython code here Teach hands-on with GlowScript

Examples

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See also

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