Answer
a. The induced current flows from left to right through resistor $R_A$ when Coil B is moved toward Coil A.
b. The induced current flows from right to left through resistor $R_A$ when Coil B is moved away from Coil A.
c. The induced current flows from right to left through resistor $R_A$ when the resistance $R_B$ in Coil B is increased.
Work Step by Step
a. The induced current flows from left to right through resistor $R_A$ when Coil B is moved toward Coil A.
Magnetic field lines created by coil B point toward the left, by the right hand rule. As coil B moves as described, the number of magnetic field lines inside coil A, pointing to the left, increases with time.
The induced current in the Coil A will cause a field to oppose this change in magnetic flux. The secondary field makes magnetic field lines through Coil A that point toward the right, by Lenz’s Law. By the right hand rule, a counterclockwise (as viewed from the right) induced current appears in the ring. This induced current flows from left to right through resistor $R_A$.
b. The induced current flows from right to left through resistor $R_A$ when Coil B is moved away from Coil A.
Magnetic field lines created by coil B point toward the left, by the right hand rule. When coil B is withdrawn as described, the number of magnetic field lines inside coil A, pointing to the left, decreases with time.
The induced current in the Coil A will cause a field to oppose this change in magnetic flux. The secondary field makes magnetic field lines through Coil A that point toward the left, by Lenz’s Law, to replace the field that is lost. By the right hand rule, a clockwise (as viewed from the right) induced current appears in the ring. This induced current flows from right to left through resistor $R_A$.
c. The induced current flows from right to left through resistor $R_A$ when the resistance $R_B$ in Coil B is increased.
Magnetic field lines created by coil B point toward the left, by the right hand rule. When the resistance $R_B$ in Coil B is increased, the current in Coil B decreases and the primary field weakens, so the number of magnetic field lines inside coil A, pointing to the left, decreases with time.
The induced current in the Coil A will cause a field to oppose this change in magnetic flux. The secondary field makes magnetic field lines through Coil A that point toward the left, by Lenz’s Law, to replace the field that is lost. By the right hand rule, a clockwise (as viewed from the right) induced current appears in the ring. This induced current flows from right to left through resistor $R_A$.
