Here’s a snippet from an article in The Atlantic:
Many observant Jews do not operate lights, computers, mobile phones, or other electrical appliances from sundown on Friday until three stars appear in the night sky on Saturday. They abstain from these activities because, over the last century, rabbinic authorities have compared electricity use to various forms of work prohibited on the Sabbath by the Bible and post-biblical rabbinic literature, including lighting a fire and building. The difficulty of interpreting the Bible’s original intent and applying it to modern technology has rendered electricity use on the Sabbath one of the more contentious topics in Jewish law.
E-readers are problematic not only because they are electronic but also because some rabbis consider turning pages on the device – which causes words to dissolve and then resurface – an act of writing, also forbidden on the Sabbath.
Much more in the article.