This spot of light, resembling in its outlines the flame, is called an image. An image is defined as an optical counterpart of an object. Images are formed in a variety of devices, such as apertures, mirrors, and lenses. The pin-hole camera is simply a light-tight box with a small aperture in one side. Light passing through this aperture forms an image upon the opposite side of the interior of the box, of whatever object is in front of the camera. Light entering a room through a large aperture such as a window produces a multitude of overlapping images which blend to form a somewhat evenly illuminated surface.
Important Topics
1. Light contrasted with sound (three differences).
2. Bodies: transparent, translucent, opaque.
3. Light: reflected, transmitted, absorbed.
4. Light travels in straight lines, evidence, shadows, umbra, penumbra.
5. Formation of images by small apertures.
Exercises
1. Consider the circumference of the earth as 25,000 miles. How many times would the speed of light cover this distance in a second?