|FIELD: Physical Science||DURATION: 1 hr|
|OBJECTIVE: Students will observe how light travels and creates images.|
|METHOD: Students build pinhole cameras and observe images it creates.|
|KEY VOCABULARY: Camera, light, aperture.||GROUP SIZE: Any|
The way we see is by light rays reflecting off objects or being emitted by them. The sun is our primary light source in the daytime and by reflecting off molecules in the air, makes the sky blue. An important fact is that light rays always travel in straight lines over non-cosmic distances (over cosmic distances, light rays will curve around a planet's gravitational field).
When a camera captures an image on film, it is exposing chemically reactive photographic film to reflected light in the world. But if we hold photographic film out in the light we get a mess, not a picture. The secret that the camera uses is the tiny opening through which it allows light to get in and hit the film: the 'aperture'. By looking at the geometry of the inside of a camera (see diagram), and knowing that light rays are always straight, you see that the aperture lets only a certain area of light outside the camera hit a certain area of the film. By restricting the light in this way, the camera can recreate fairly effectively a picture of the outside world.
The pinhole camera works on the same principal as a normal camera except without the expensive film. Instead, it uses a piece of wax paper that you look at directly, while the light is still shining on it.
In this experiment you will construct a pinhole camera and see how its aperture works to restrict the light and create an image of the outside world.
MATERIALS (per group):