An electric door lock contains a permanent magnet and an electromagnet.
What are suitable materials for the permanent magnet and for the core of the electromagnet?
1 )
permanent magnet: soft iron / core of electromagnet: soft iron
2 )
permanent magnet: soft iron / core of electromagnet: steel
permanent magnet: steel / core of electromagnet: soft iron
4 )
permanent magnet: steel / core of electromagnet: steel
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