When Apple wants to make a big splash, it returns to its history. Thirty years ago at the Flint Center for the Performing Arts, a roomy auditorium in Cupertino, Calif., Steven P. Jobs introduced the original Macintosh. On Tuesday, Apple will come back to the center to unveil a set of long-anticipated products: two iPhones with larger screens, and a wearable computer that the media has nicknamed the iWatch. The so-called smartwatch will be the first brand-new product unveiled under Apple’s new chief, Timothy D. Cook, who took the helm after Mr. Jobs died nearly three years ago. It is expected to come in two sizes and combine functions like health and fitness monitoring with mobile computing tasks like displaying maps, said people knowledgeable about the product. It will have a unique, flexible screen and, like the new phones, will support technology that allows people to pay for things wirelessly.