 This is a simple box with no sides. The top has been removed in this diagram so you can see the path of each ball as it is rolled through the box. This device can simulate the Rutherford scattering experiment. Balls can be rolled through the box, and the person rolling the ball can't see the obstacle that's in there, which should be small compared to the size of the boards. (We've shown it larger here for clarity). Most of the balls (1) will pass right through; a few (2) will be deflected slightly, and a very small number (3) will be deflected at large angles. Students can make guesses at what's in there, and what shape it is. The truncated curved shape in the centre can be anything that has curved sides, but it should not have a lip on the bottom. Finding just the right shape is the challenge! We've tried a thin circular piece of stretchy balloon rubber, glued and stapled all around its edge to the bottom board, and pulled upwards at the centre and attached to the top board. Attaching it was not easy ... next time we build one of these, we're going to find a plastic object that's shaped just right! [NOTE: This curved shape (representing the nucleus) in the centre actually has a proper shape, such that the height of any point on its surface should be proportional to 1/r, where r is the distance of that point from the centre of the shape. But for purposes of the demonstration, that much accuracy is probably unnecessary.] |