A bar magnet's north pole is moved toward a coil whose ends are connected to form a closed circuit. Which correctly describes the direction of the induced current in the coil?

Answer: B. The end of the coil facing the magnet becomes a north pole, opposing the magnet's approach

By Lenz's law, the induced current flows in the direction that opposes the change in flux through the coil. As the north pole approaches, the flux through the coil increases, so the current flows to create opposing flux, making the near end a north pole that pushes the magnet back. When the magnet is withdrawn the direction reverses and the force tends to hold it back. A current that aided the change would violate conservation of energy, so this direction corresponds to energy conservation.

• A. Attracting the magnet would aid the change in flux—the opposite of Lenz's law.
• B. Correct. The current opposes the increase in flux and pushes the magnet back.
• C. When the moving magnet changes the flux through the coil, an induced current flows.