I want to know if the iPad is a capacitive screen? Some ipads are available with iPad pencils, so what is the principle of iPad pencils?
ipads use capacitive screens for normal touch operation.
Capacitive screens are more versatile that resistive ones as they do not need pressure to operate; dragging or zooming etc. are easy on a capacitive screen, while I'm not sure if any resistive ones support that type of multi-finger operation at all?
The Apple Pencil, from what I've seen and what I can find online, is a "digitiser" stylus (eg. inductive coupling, not capacitive) with extra features for pressure & gesture sensing. That's presumably why it can only work with certain ipad models, that have the digitiser array included in the screen.
It appears Apple licence the digitiser tech from Wacom.
Digitisers, originally as separate tablets for such as creating or digitising engineering drawings, rather than integrated with screens, have been around since the 70s. A "puck" rather than stylus was common, combining mouse style buttons and a cross-hair alignment area for high accuracy.
https://twitter.com/x/status/1292882350741827584
Dual-mode screens are not that new and certainly not an Apple innovation, as my 10+ year old CF19 laptop has a touch + digitiser stylus screen.