Two coils are wrapped around an iron bar as shown above. Whenthe switch is close

Question

Two coils are wrapped around an iron bar as shown above. Whenthe switch is closed

A)a current momentarily passes through Rfrom right to left.
B)a current momentarily passes through R fromleft to right..
C)a constant current circulates through Rfrom right to left.
D)a constant current circulates through R fromleft to right.
E)no current passes through R. Hint: When the switch is closed current starts flowing through thecoil in the direction shown in the figure above. During somesmall time interval the current and therefore the magnetic fieldare changing, from zero to their steady-state values. Duringthat small time interval an emf is induced and a current flows inthe other circuit. That current flows so as to oppose theincrease of the magnetic field from zero to some final valuepointing towards the right. It produces a magnetic fieldpointing towards the left and must therefore momentarily flow asshown in the figure.

A)a current momentarily passes through Rfrom right to left.
B)a current momentarily passes through R fromleft to right..
C)a constant current circulates through Rfrom right to left.
D)a constant current circulates through R fromleft to right.
E)no current passes through R. Hint: When the switch is closed current starts flowing through thecoil in the direction shown in the figure above. During somesmall time interval the current and therefore the magnetic fieldare changing, from zero to their steady-state values. Duringthat small time interval an emf is induced and a current flows inthe other circuit. That current flows so as to oppose theincrease of the magnetic field from zero to some final valuepointing towards the right. It produces a magnetic fieldpointing towards the left and must therefore momentarily flow asshown in the figure. Hint: When the switch is closed current starts flowing through thecoil in the direction shown in the figure above. During somesmall time interval the current and therefore the magnetic fieldare changing, from zero to their steady-state values. Duringthat small time interval an emf is induced and a current flows inthe other circuit. That current flows so as to oppose theincrease of the magnetic field from zero to some final valuepointing towards the right. It produces a magnetic fieldpointing towards the left and must therefore momentarily flow asshown in the figure.

Explanation / Answer

When the switch is closed, the left coil momentarily increasescurrent which creates a momentary increase in magnetic field to theright through the right coil. This causes an induced current in theright coils that flows opposite the direction the current in theleft coil, i.e. it flows from right to left through theresistor. . So the answer isA

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