A Plotting Compass (Two Glass Face) is a compact, specialized tool used for mapping magnetic field lines in physics experiments. Unlike standard navigation compasses, these are designed to be used in multiples to provide a "frame-by-frame" look at magnetic flux.
Specifications
- Dual Glass Faces: Both the top and bottom are made of glass, allowing for clear visibility and the ability to use the compass on an overhead projector or light box.
- Size: Each compass has a standard 20 mm diameter.
- Packaging: Typically supplied as a pack of 10, which is ideal for individual student use or mapping a full magnetic field around a single magnet.
Primary Uses in the Lab
- Mapping Magnetic Fields: By placing several compasses around a bar or horseshoe magnet, students can see exactly where the field lines curve from North to South.
- Successive Plotting: One compass can be used to trace a field line. A student marks the position of the needle's tip, moves the compass tail to that mark, and continues until a full loop is drawn on paper.
- Electromagnetism: Used to detect the weak magnetic fields created by a current-carrying wire (Oersted's Experiment).
Maintenance TipBecause these needles are small and sensitive, they can sometimes have their polarity reversed if they are stored too close to a very strong neodymium magnet. To prevent this, always store them in their original packaging away from heavy-duty magnets.