A Conducting Bar Moves as Shown near a Long Wire

A conducting bar moves as shown near a long wire carrying a constant 50-A current. If a = 4.0 mm, L = 50 cm, and v = 12 m/s, what is the potential difference, VA − VB?

A) +15 mV
B) −15 mV
C) +20 mV
D) −20 mV
E) +10 mV