chapter 10: waves

amplitude (waves)

The maximum displacement from the equilibrium position (can be positive or negative)

angle of incidence

The angle between the direction of travel of an incident wave and the normal at a boundary between two media

angle of reflection

The angle between the direction of travel of a reflected wave and the normal at a boundary between two media

antiphase

Particles oscillating completely out of step with each other (one reaches its maximum positive displacement as the other reaches its maximum negative displacement) are in antiphase

coherence

Two waves sources

compression (waves)

A moving region in which the medium is denser or has higher pressure than the surrounding medium

constructive interference

Superposition of two waves in phase so that the resultant wave has greater amplitude than the original waves

critical angle

The angle of incidence at the boundary between two media that will produce an angle of refraction of 90 °

crystallography

A method for determining the structure of a substance by studying the interference patterns produced by waves passing through a crystal of the substance

destructive interference

Superposition of two waves in antiphase so that the waves cancel each other out and the resultant wave has smaller amplitude than the original waves

diffraction

The phenomenon in which waves passing through a gap or around an obstacle spread out

displacement (waves)

The distance from the equilibrium position in a particular direction — displacement is a vector

electromagnetic spectrum

The full range of frequencies of electromagnetic waves

electromagnetic wave

Transverse waves with oscillating electric and magnetic field components

equilibrium position (waves)

The resting position for particles in the medium

frequency (waves)

The number of wavelengths passing a given point per unit time

fundamental frequency

The lowest frequency at which an object (e.g.

fundamental mode of vibration

A vibration at the fundamental frequency

gamma rays

Short-wavelength electromagnetic waves

harmonic

A whole-number multiple of the fundamental frequency

in phase

Particles oscillating perfectly in time with each other (reaching their maximum positive displacement at the same time) are in phase

infrared waves

Electromagnetic waves

intensity (waves)

The radiant power passing through a surface per unit area

interference

Superposition of two progressive waves from coherent sources to produce a resultant wave with a displacement equal to the sum of the individual displacements from the two waves

interference pattern

A pattern of constructive and destructive interference formed as waves overlap

law of reflection

The angle of incidence is equal to the angle of reflection

longitudinal wave

A wave in which the medium is displaced in the same line as the direction of energy transfer — oscillations of the medium particles are parallel to the direction of the wave travel

maximum (waves)

The point of greatest amplitude in an interference pattern

microwaves

Long-wavelength electromagnetic waves

minimum (waves)

The point of least amplitude in an interference pattern

monochromatic light

Light of a single frequency

node

For a stationary wave

normal

An imaginary line perpendicular to a surface such as the boundary between one medium and another (e.g.

optical fibre

A fibre made of glass designed with a varying refractive index in order to totally internally reflect pulses of visible or infrared light travelling through it

out of phase

Particles that are neither in phase

partially polarised

Description of a transverse wave in which there are more oscillations in one particular plane

path difference

The difference in the distance travelled by two waves from the source to a specific point

peak

The maximum positive amplitude of a transverse wave

period (waves)

The time taken for one complete wavelength to pass a given point

phase difference

The difference between the displacements of particles along a wave

plane polarised

Description of a transverse wave in which the oscillations are limited to only one plane

polarisation

The phenomenon in which oscillation of a transverse wave are limited to only one plane

polycrystalline graphite

Thin layers of graphite with regularly arranged carbon atoms in different orientations

principle of superposition of waves

When two waves meet at a point the resultant displacement at that point is equal to the sum of the displacements of the individual waves

progressive wave

A wave in which the peaks and troughs

P-waves

Primary waves — longitudinal waves that travel through the Earth from an earthquake

radio waves

Long-wavelength electromagnetic waves

rarefaction (waves)

A moving region in which the medium is less dense or has less pressure than the surrounding medium

ray

A line representing the direction of energy transfer of a wave

reflection

The change in direction of a wave at a boundary between two different media

refraction

The change in direction of a wave as it changes speed when it passes from one medium to another

refractive index

The refractive index of a material v c n 

standing wave

A wave that remains in a constant position with no net transfer of energy and is characterised by its nodes and antinodes — also called a stationary wave

stationary wave

A wave that remains in a constant position with no net transfer of energy and is characterised by its nodes and antinodes — also called a standing wave

superposition (waves)

Overlap of two waves at a point in space

S-waves

Secondary waves: transverse waves that travel through the Earth from an earthquake

total internal reflection

The reflection of all light hitting a boundary between two media back into the original medium when the light is travelling through the medium with the higher refractive index and the incidence angle at the boundary is greater than the critical angle

transverse wave

A wave in which the medium is displaced perpendicular to the direction of energy transfer — the oscillations of medium particles are perpendicular to the direction of travel of the wave

trough

The maximum negative amplitude of a transverse wave

ultraviolet

Electromagnetic waves

unpolarised

Description of a transverse wave in which the oscillations occur in many planes

visible light

Electromagnetic waves

wave equation

An equation that relates the frequency ƒ in hertz

wave profile

A graph showing the displacement of the particles in the wave against the distance along the wave

wave speed

The distance travelled by the wave per unit time

wavefront

A line of points in phase with each other in a wave

wavelength

The minimum distance between two points oscillating in phase

X-rays

Short-wavelength electromagnetic waves