In: Physics
What happens to the image if you cover half of the
lens with an index card? Perform the experiment (be careful to
cover the lens, not the object), and record your observation.
Explain your observation. Explain your observation and draw ray
diagrams to support your arguments.
- --- - -- ---- When you cover half the lens you get a fainter image. Effectively you are cutting out half the light rays, but they still produce an entire image. In the diagram below you can see that rays from the top and bottom of the tree still pass through the top half of the lens to form. However half of the rays from all parts of the image are blocked, so that only half reach the image point, giving only half the intensity of the complete lens. Note: it is particularly valuable to get students to predict what will happen in advance of doing the activity, as it is not an intuitive result for many people. object image object image complete lens - bright image half covered lens - faint image