A rectangular coil lies flat on a horizontal surface. A bar magnet is held above the center of the coil with its north pole pointing down. What is the direction of the induced current in the coil?
Answered on
The direction of the induced current in the coil can be determined by using Lenz's Law, which states that the direction of any induced current is such that it will oppose the change causing it. In this case, the changing magnetic field is due to the bar magnet being brought closer to the coil.
As the north pole of the magnet is brought closer to the coil, the magnetic field lines through the coil are directed downward. According to Lenz's Law, the coil will generate a current that creates a magnetic field to oppose this increase. To oppose the downward magnetic field of the bar magnet, the coil will create its own magnetic field with a north pole facing up towards the magnet.
To know which way the current flows in the coil to create such a magnetic field, you can use the right-hand rule: if you point your thumb in the direction of the desired magnetic field (in this case, upwards), your fingers will curl in the direction of the current.
Therefore, for a rectangular coil lying flat on a horizontal surface with a north pole of a magnet approaching it from above, the induced current will flow in such a direction as to create a north pole on the upper side of the coil, which means the current flows counterclockwise when viewed from above.