Two seperate but similiar coils of wire are mounted close to eachother (Primary

Question

Two seperate but similiar coils of wire are mounted close to eachother (Primary and Secondary.) The primary coil is connected to a battery and the secondary coil is connected to a current meter. Consider the following situations: (1) The switch is open and there is no current in the primary. (2)As the switch is being closed, the current in the primary is rapidly rising toward its maximum value. (3) The switch is closed and there is a steady current in the primary. (4)As the switch is being openned, the current in the primary is rapidly falling to zero. In which of those situations will the current meter indicate a current flowing in thesecondarycoil? Select all that apply.

Explanation / Answer

When the switch is closed, the magnetic field around the first coil builds up inducing a current in the second coil; this shows in the galvo as a short 'kick' in one direction. When the switch is open the magnetic field in the first coil collapses inducing a current in the galvo but this time giving a 'kick' in the opposite direction. This reversal in the direction of current flow is due to the reversal in the magnetic field around the first coil. The induced currents only occur when the magnetic field of the first coil is changing (IOW when in the transient state) No current is induced when the magnetic field or lack of it has stabilized.

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