Permanent magnets generate a constant magnetic field, and electromagnets gen- erate a field only when an electric current is passed through them.
(Permanent magnets; generate; a constant magnetic field) (Permanent magnets; electromagnets gen; erate a field) (an electric current; is passed; through them)
Permanent magnets Permanent magnets an electric current
generate electromagnets gen is passed
a constant magnetic field
erate a field
through them