My standalone mongodb uses only 1core out of 4 available cores , why?

Above is screenshot from mongodbSingleInstance setup(production). i monitored for almost 10minutes, for almost 95% of the 10minutes, i can see cpu utilization only in a singlecore as shown in screenshot. All other cores are simply sitting there.
This is a singleInstanceMongodb setup.

reason for 100% utilization: search query running on a collection with >8lakh records, required for batchprocessing(can it be improved? yes).
My doubt is, if there are multiple searchqueryrequests for a same collection, shouldn’t it be scheduled to different cores?

  1. if searchquery1Request and searchquery2Request reach mongodb server at the sameTime and both are targeting the same collection, will searchquery1Request put a lock on entire collection? since its a readRequest i think there will be nolocks on collection, if there are no locks on collections then will these 2 requests execute in 2 different cores?

i created below question in this forum , and i received answer like “mongodb will use multi-cores” . my question is how can i prove that mongodb making use of multiple cores?

@Doug_Duncan if you could share your understanding on this topic , it would be helpful

thank you