Refraction of waves
Waves A wave is passed across or through a material (medium), eg light waves are transmitted through air, glass and water. at the interface (boundary) between two materials may change direction. Process by which a wave changes speed and sometimes direction upon entering a denser or less dense medium, eg a light ray changes direction when refracted by a lens. is the change in direction of a wave at such a boundary. All wave types can be refracted.
It is important to be able to draw Diagram that represents the direction and angle of travel of light. to show the refraction of a wave at a boundary.
Explaining refraction - Higher
The A measure of compactness and the ratio of mass to volume. It is usually measured in kilograms per metre cubed (kg/m3) or grams per centimetre cubed (g/cm3). of a material is one of the factors that affects the speed that a wave will be transmitted through it.
Wave speed, frequency and wavelength in refraction
For a given The number of waves produced each second. The unit of frequency is hertz (Hz). of light, the The length of a single wave, measured from one wave peak to the next. is A relationship between two variables, eg in a gas. As temperature increases, the pressure would also increase proportionally. (If the temperature doubled, the pressure would double). to the wave speed:
wave speed = frequency × wavelength
So if a wave slows down, its wavelength will decrease. The effect of this can be shown using wave front diagrams, like the one below. The diagram shows that as a wave travels across a boundary from air to water it slows down and the wavelength decreases. Although the wave slows down, its frequency remains the same, due to the fact that its wavelength is shorter.
In this diagram, light waves move from air into water. Light waves move slower in water. The right hand side (the bottom edge) of the incoming wave slows down before the left hand side does. This causes the wave to change direction.
If the wave were crossing the boundary in the opposite direction, the waves would speed up, and the same path would be taken in reverse.
The amount that the wavelength is changed affects the amount that the direction changes. The amount of wavelength change depends on the differences between the material on each side of the interface. For example, in the diagram, replacing the water with a material with a greater optical density (like glass) would cause a bigger change in speed and so a bigger change in direction.
