A Rod Lies Across Frictionless Rails in a Uniform Magnetic

Multiple Choice

A rod lies across frictionless rails in a uniform magnetic field B, as shown. The rod moves to the right with speed v. In order for the emf around the circuit to be zero, the magnitude of the magnetic field should:

A) not change
B) increase linearly with time
C) decrease linearly with time
D) increase quadratically with time
E) decrease quadratically with time