SAN FRANCISCO — Apple is back with a refined second-generation tablet computer that squeezes more power into a thinner shell while keeping prices in check. It’s a three-pronged push that should handily hold off competitors for another year.

Underscoring the tablet’s importance to Apple, CEO Steve Jobs briefly emerged from a medical leave Wednesday and made a surprising appearance to unveil the iPad 2 himself.

With the original iPad, Apple proved there is great demand for a tablet that’s less than a laptop and more than a smart phone, yet performs many of the same tasks. Dozens of copycat touch-screen devices are in the works, but so far none has broken into the mainstream consciousness the way the iPad has.

“The competition is essentially going to be picking up the crumbs that Apple decides to leave behind,” said Ashok Kumar, an analyst with Rodman & Renshaw.

He said the number of software applications available for the iPad gives Apple a huge advantage.

“Is the tablet market anything beyond the iPad?” Kumar said. “So far the answer is no.”