Night 1 · Core lab
Map a bar magnet with a compass
Parts · Small classroom bar magnet with marked poles, compass, ruler, paper, and tape.
1Predict
Sketch the baseline. Predict how the needle will move when you flip the magnet and when you move it farther from the compass.
Help with the prediction
The compass follows the local combined field. Flipping the magnet reverses its contribution. Moving it farther away usually makes its contribution smaller.
2Set up the station
Use a nonmagnetic surface and small classroom magnets. Move steel tools and other magnets away. Keep the compass flat.
Reveal the setup diagram
- With the magnet away from the compass, mark the resting needle direction as zero. Clockwise is positive. Counterclockwise is negative.
- Mark a line through the compass center perpendicular to the baseline. Place the bar on this line, with the marked pole facing the compass.
- Start with the nearest pole about 5 cm from the compass center. Flip it end for end at the same mark, then return to the original pole and move it to about 10 cm. If the needle barely moves, adjust the two distances and record them.
3Measure and check
Record signed angles relative to your baseline. Repeat an unexpected reading before changing the setup.
4Explain
What stayed fixed when you reversed the poles? Why does the compass tell you local direction without giving the field in teslas?
Optional extension
Move the compass around the stationary bar and draw arrows at six locations. Use the same compass face and note where the arrows turn.
Show the instructor your setup, readings, and explanation.