1. OR is all capital letters
Effective: [uk OR england]
Ineffective: [uk Or england]
Ineffective: [uk or england]
2. OR acts on the words touching it
Effective: [“tesla coil” OR “jacobs ladder”]
Ineffective: [tesla coil OR jacobs ladder]
Generally, OR only applies to the words directly on either side of it, so search engines read [tesla coil OR jacobs ladder] with the OR only applying to coil and jacobs.
Google interprets this query to mean that you want all the pages to have the words tesla and ladder, since they are not next to an OR. Only putting the two names in quotes, you make the OR apply to tesla coil and jacobs ladder as set phrases.