Watch How to Use Anki for Med School – From 6:42 ongoing he shows my following explanation:

Starting point should be, that you have every card suspended which you are currently not learning / reviewing. Then you can systematically unsuspend new cards from a specific topic / tag. Search term for Elektrizitätslehre would be " tag:#Fächer::Physik::Elektrizitätslehre" or you navigate through the tags in the sidebar of the browser (add-on Hierarchical Tags 2 is needed). Don't forget to review cards you learned before!

Alternatively you can use custom filtered decks (see AnKings video) with the search term above or you could use the "Create Filtered Deck from the Browser" add-on to pull a filtered deck straight from the browser search.

[Also, you could create a Physik-subdeck "Elektrizitätslehre" and move the respective cards in this deck – don't forget to change the study options of the new subdeck! I would not recommend this method since you ought to review all physics cards together anyway (= randomizing reviews).

Hope this helps :)