If the same visitor views the same page 10 times, and this page has 4 ads, does this mean the page generated 40 ad impressions?
It depends. The likely reason behind lifting original limit of 3 ads per page is due to the fact that present-day searches & site visits are primarily from mobile devices. Since the user has to scroll to see additional content, it only makes sense that pages with more content can handle more ads.
Is a user going to read your page 10 times start to finish from a mobile device - well, maybe. If they do - then 40 ad impressions are generated, assuming that they were visible to the user.
Same goes for desktop if the ads are above and below the fold, and the user views the entire page - then you have your page views. 10x more times get you to 40.
But the important question you should be asking yourself is what the impact this will have on advertisers. Will this help your earning potential with many impressions but no clicks? AdSense can prove to be a game of less is more. Make sure you are providing useful content to your visitors - and if they decide to read your page 10 times, then I believe that you must have succeeded!
Yes, An impression is counted for each ad request that returns at least one ad to the site. It is the number of ad units (for content ads) or search queries (for search ads) that showed ads.
If you have 4 ads on a page,
One Pageview = 4 ad Impressions
Suppose, you get 5 clicks out of 500 ad impressions, your CTR would be 1% (5/500X100).