I cannot praise the "For Beginners" series highly enough. They are set out like cartoon books, so they are easy to read, but the cartoons are there to space out the text. You can rip through something that would be deadly dull otherwise. Try this one for starters:
So everyone knows Stephen Hawking. He does Physics. People say he's the cleverest man in the world. He was at the Paralympics opening ceremony. He talks through a computer. He's been on The Simpsons. But do you know what theory he is famous for? And if you do, do you understand it? This book takes you though some of Einstein's theory of General Relativity to the discovery of black holes and then Hawking's reasons for believing that they can evaporate. It also tells some of the story of Hawking's life.
Borrow it from the school library and read it. I dare you.