A wave is a traveling disturbance that transfers energy and information; mechanical waves such as sound need matter, while electromagnetic waves such as light can cross a vacuum.

What moves when a wave travels?

A wave transfers energy and information through a disturbance. The material in the medium usually moves back and forth around an equilibrium position instead of traveling with the wave over a long distance. A marked point on a rope rises and falls while the pulse moves along the rope.

How do wavelength, frequency, and speed fit together?

Wavelength is the distance between matching points on neighboring cycles. Frequency is the number of cycles passing a point each second. Wave speed equals frequency multiplied by wavelength. In one medium, a higher frequency therefore pairs with a shorter wavelength when speed stays constant.

Why does sound need matter?

Sound is a mechanical wave. It travels through vibrations in matter, so it cannot cross a vacuum. Frequency is closely connected to pitch. Amplitude and intensity are connected to loudness, although human hearing is more complicated than a one-number rule.

How is light different from sound?

Light is an electromagnetic wave and can travel through a vacuum. All electromagnetic waves have the same speed in a vacuum but differ in frequency and wavelength. Radio waves, visible light, ultraviolet radiation, and X-rays belong to the same spectrum.

What happens at a boundary?

Reflection sends a wave back. Refraction changes its direction because its speed changes in a new medium. Absorption transfers wave energy to matter. Diffraction spreads a wave around an edge or through an opening. Interference occurs when overlapping waves combine.

Common trap: a wave’s frequency is set by its source. When light enters a new medium, speed and wavelength can change while frequency stays the same.

How do you solve a wave question?

Name the wave, identify the medium, decide which quantity changes, and use the relationship among speed, frequency, and wavelength only after the physical story is clear. A formula is most useful when each symbol already has a meaning.