An investigator uses a miniature dipping needle to study the magnetic field around a powerful bar magnet. The dipping needle is mounted such that it is free to rotate in a vertical plane parallel to the long axis of the bar magnet.
Describe how the orientation of the dipping needle changes as it is moved along a line directly above the bar magnet, starting from a position directly over its South pole and ending directly over its center (equator).
Explain how this observation relates to the direction of the magnetic field lines near the surface of the bar magnet.
An engineer sets up an experiment to investigate the magnetic field surrounding a vertical conduit carrying a heavy DC power cable that passes through a horizontal flat wooden sheet.
Describe how the engineer can use a single small plotting compass to map the exact shape of a magnetic field line on the horizontal sheet.
The diagram below shows the vertical conduit carrying a current I I\,I that flows vertically downwards through the horizontal sheet.
State the geometric shape of the magnetic field lines and determine their direction (clockwise or anticlockwise) when viewed from directly above.