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,V_A - V_B?

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