Chapter 4 Many properties of light can be understood using a wave model of light. Vocabulary

Section 4.1 The Nature of Light

Pythagoras A Greek philosopher who believed that light beams were made up of tiny particles. A Greek philosopher who believed that light beams were made up of tiny particles.

Microscope An optical device used to magnify extremely small objects, such as micro- organisms; composed of a combination of lenses.

Telescope An optical device used to magnify distant objects, such as stars and planets; composed of a combination of lenses or lenses and mirrors.

Section 4.2 Properties of Waves

Wave A disturbance or movement that transfers energy through matter or space, without causing any permanent displacement.

Crest The highest part of a wave.

Trough The lowest part of a wave.

Wavelength Distance from one wave crest to the next; length of one unit of a wave that repeats itself.

Amplitude The distance between the highest point (crest) on a wave and the rest position; also, the distance between the lowest point (trough) and the rest position.

Frequency The number of repetitive motions, or vibrations, of a wave that occur in a given amount of time; measured in cycles per second or Hertz (Hz).

Energy The capacity to apply force over a distance.

Force Anything that causes a change in the motion of an object; a push or pull on an object.

Compression Waves A wave for which the action making the wave is back and forth along the direction in which the wave is moving.

Transverse Waves A wave for which the action making the wave is perpendicular to the direction in which the wave is travelling.

Hertz Cycles per second; unit used to measure frequency of a wave.

Medium The material or substance through which a wave is moving.

Section 4.3 Properties of Visible Light

Visible Light A form of energy that you can detect with your eyes.

Spectrum The array of colours of light that result from the separation or dispersion of white light.

Wave Model of Light A model in which light is a type of wave that travels through space and transfers energy from one place to another.

Reflection The process in which light or another type of wave interacts with a surface and is sent back from the surface.

Refraction The changing of direction or bending of light or other type of wave when travelling from one medium to another medium having a different density.

Section 4.4 Light and the Electromagnetic Spectrum

Radiant Energy Energy, such as light, that spreads out from a source in all directions.

Electromagnetic Radiation A repetitive movement, not of particles, but of electric and magnetic energy through space.

Radio Waves Electromagnetic waves having wavelengths from a few centimetres to several kilometres long.

Ultraviolet Waves Electromagnetic waves with wavelengths between 4 × 10 –7 m and 4 × 10 –9 m.

X-rays Electromagnetic waves with very short wavelengths, between about 3 × 10 –9 m and about 1 × 10 –12 m.

Microwaves Electromagnetic waves having wavelengths between 0.3 cm and 30 cm.

Infrared Waves Electromagnetic waves having wavelengths between 3 × 10 –4 m and 7 × 10 –7 m.

Gamma Rays The portion of the electromagnetic spectrum with the highest energy, highest frequency, and lowest wavelength; result from nuclear reactions; used in cancer therapy.