Light: Straight-Line Propagation, Shadows, Reflection and Mirrors
How light travels in straight lines, casts shadows, and bounces off surfaces
Big Idea: In a uniform transparent medium light travels in straight lines. This single fact explains why objects cast sharp shadows, why we see images in a mirror, and why the law of reflection has such a clean form: the angle of incidence equals the angle of reflection. Optics begins here.
By the end you will be able to:
- tell a luminous source from an illuminated body;
- use the rectilinear (straight-line) propagation of light to explain shadows and eclipses;
- distinguish a shadow from a penumbra;
- state and apply the law of reflection with the normal;
- describe the image in a plane mirror (virtual, upright, same size, laterally reversed, equally far behind).