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PRACTICE / Motional EMF

A moving rod can have voltage without a circuit.

A conducting rod of length 0.50 m moves right at 3 m/s. The rod is vertical and a uniform 0.40 T magnetic field points into the page.

What is the potential difference between the upper and lower ends in magnitude, and which end is positive?

Organize the givens & assumptions
  • Rod length: 0.50 m
  • Speed: 3 m/s
  • Field: 0.40 T into the page

The rod is open-circuit and has reached transverse charge equilibrium. Velocity, rod length and magnetic field are mutually perpendicular.

  1. A0.60 V, upper end positive0.60\ \mathrm V,\ \text{upper end positive}
  2. B0.60 V, lower end positive0.60\ \mathrm V,\ \text{lower end positive}
  3. C0 V0\ \mathrm V
  4. D6.0 V, upper end positive6.0\ \mathrm V,\ \text{upper end positive}

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