Idea 3of 7Builds onThe invisible map
Where the lines crowd
How do you draw something you cannot see?
Today you'll discover
- how to draw a map of the invisible
- what a crowded part of the map means
- the three rules every map obeys
Think firstIron filings sprinkled round a magnet gather into curves
Iron filings sprinkled round a magnet gather into curves. What are the curves?
Decide first, then press Next. Watch where the curves crowd together.
A bar magnet with its north end shaded. After a prediction, one curved loop appears leaving the north end and entering the south, then a whole family of loops that crowd near the poles, then a compass whose needle lies along the loop through it. The last step asks whether there is a field in the gap between two drawn lines.
See the whole ideathe big idea and the key word, in one place
The big idea
Field lines map the field: direction along, strength by crowding.
Easy to get wrongA field line is not a path anything travels along, and the field does not stop between lines. Draw more lines and nothing changes but the map.
Key word
- field line
- a line drawn along the field's direction; closed loops out of north into south, never crossing, crowded where the field is strong
About this modelField lines are closed loops that never cross; a compass needle lies along the line where it sits.
Field lines are closed loops that never cross; a compass needle lies along the line where it sits.
Ready to use it?
- Sketch the field lines of a bar magnet and say where the field is strongest.