磁体通上直流电,此体内的电磁铁因为通过电流而形成磁场,当触头位于磁场里时,触头闭合,当断开加在磁体上的直流电,去掉外界磁场时,触头接点断开.另外,磁体在通电的情况下,若将磁体接近触头（后让锄头接近磁体）则触头接点闭合.反之,若将磁体与触头远离,则因磁场变弱,触头接点断开
Electrify the magnet with direct current ,the magnet then form a magnetic field by the electric current.When the contact is placed in the magnetic field ,it would close.When the electric current is cut off,the contact close.What's more,when the contact is electrified ,get the magnet near the contact(then get the contact near the magnet),the contact would close.On the other hand,if the contact is moved away,the contact close because of the magnetic field weakening.