Motional Emf: a Conducting Bar Slides Without Friction on Two

Multiple Choice

Motional emf: A conducting bar slides without friction on two parallel horizontal rails that are 50 cm apart and connected by a wire at one end. The resistance of the bar and the rails is constant and equal to 0.10 Ω. A uniform magnetic field is perpendicular to the plane of the rails. A 0.080-N force parallel to the rails is required to keep the bar moving at a constant speed of 0.50 m/s. What is the magnitude of the magnetic field?

A) 0.10 T
B) 0.25 T
C) 0.36 T
D) 0.54 T
E) 0.93 T