Light: notes

Reflection

• Law of reflection: the angle of incidence equals the angle of reflection, both measured from the normal.
• Plane mirror image: upright, the same size, as far behind the mirror as the object is in front, and laterally inverted.

Refraction

• Refraction: light bends at a boundary because its speed changes. Going into glass it bends toward the normal.
• Refractive index: n = sin i / sin r. Light of speed 3.0 x 10⁸ m/s in air is slower in glass.
• Total internal reflection: happens when light in glass or water meets the edge at more than the critical angle. Optical fibres use it.

Lenses

• Converging (convex) lens: brings parallel rays to a focus. Used in cameras, magnifying glasses and projectors.
• Focal length: the distance from the lens to the focus.
• Real image: can be shown on a screen. Virtual image: cannot, and is seen through the lens.

Colour

• Dispersion: a prism splits white light into red, orange, yellow, green, blue, indigo and violet.
• Electromagnetic spectrum: all its waves travel at 3.0 x 10⁸ m/s in a vacuum.