Answer:
Magnetic field patterns of two permanent magnets.
Step-by-step explanation:
From the attached picture, it can be observed that iron filings has been caused to align with respect to the magnetic fields of permanent the magnets. The concentration of the filings at some definite spots shows the poles of the magnet. This forms a magnetic field pattern.
This simply illustrates the effect of magnetic fields on iron filings by placing magnets below a paper or cardboard with iron filings on the top of the paper. The magnetic field pattern would be lost if the magnets are removed.