It is the same question which I have mentioned at On-topic question about wavelengths. It took several edits for the question to be reopened. Yet, my question has 6 downvotes and 1 upvote. Apart from all the edits that I made to reopen the question, what further improvements not prevent the question from getting downvotes.
6$\begingroup$ Note that voting is confidential - basically no one has to state why they vote up or down or identify themselves. This is just how the site works (to avoid vendettas). We all simply have to accept the down or up votes and get on with our lives. $\endgroup$– StephenG - Help UkraineMay 2 at 23:08
Downvotes mean, according to the tooltip when you hover over the button, that the question is unclear or not useful. Users have also described using downvotes to indicate that a question shows a lack of research effort, or that they think the question is off-topic.
Note that users who downvote a question may or may not see that question again to reconsider their vote. The question may not appear in the activity lists which the previous voters use to explore the site; they may see the title and not click into the question to see what has changed; they may view the changes and decide that the question still merits their downvote. Note that Meta questions (like yours here) bring visibility to the questions they link, for good or for ill.
Users are not required nor expected to publicly explain their votes, so for a detailed explanation of the votes you are out of luck unless a voter volunteers. Try not to worry about it too much; just ask better questions on the future.
This version of the question is unclear: you can get an answer in most textbooks, web sources (such as this one) or in many videos. So what exactly do you want?
If not for the bounty, the current version of the question would likely be closed again.