Longitudinal waves: the vibrations are parallel to the direction of the wave (sound) e.g. | | | ||| ||| | | ||
Transverse waves: the vibrations are perpendicular to the direction of the wave (water, EM waves)
Wavelength: the distance from a point on one wave to the equivalent point on the adjacent wave.
Amplitude: the maximum displacement of a point on a wave away from its undisturbed position (high amplitude = high volume).
Frequency: the number of waves passing a point each second (high frequency = high pitch).
Period: the time taken for one wave to pass a point.
T = 1/f
v = fλ
T: time period (s), f: frequency (Hz), v: speed (m/s), λ: wavelength (m)
Electromagnetic waves are always transverse, travel at the same velocity through a vacuum.
HIGHEST WAVELENGTH, LOWEST FREQUENCY
Uses: RADIO: tv and radio, MICROWAVES: satellite communications, cooking food, INFRARED: electrical heaters, cooking food, infrared cameras, VISIBLELIGHT: fibre optic communications, ULTRAVIOLET: energy efficient lamps, sun tanning, X-RAYS and GAMMA: medical imaging and treatments.
LOWEST WAVELENGTH, HIGHEST FREQUENCY
Radio waves can be produced by oscillations in electrical circuits.
When they are absorbed they may create an alternating current with the same frequency, so radio waves can themselves induce oscillations in an electrical circuit.
Different substances may absorb, transmit, refract or reflect electromagnetic waves.
Refraction: when waves change direction as they enter a new medium. For example, when light enters glass from air, it slows down, so it bends (towards the normal).
Diagrams: the normal is perpendicular (90 degrees) to the boundary. If the ray slows down, it bends towards the normal. If it speeds up, it bends away from the normal.
Reflection: when a wave bounces back off a surface.
Triple Science Only
Angle of incidence = angle of reflection (measure both using the normal).
Sound waves can travel through solids causing vibrations.
In the ear, sound waves cause the ear drum to vibrate which causes sound.
The frequency range of human hearing is 20-20,000 Hz.
Ultrasound waves have a frequency above 20,000 Hz.
Ultrasound waves are partially reflected when they meet a boundary between two media. The time taken for the reflections to reach a detector can be used to determine how far away such a boundary is. This allows ultrasound waves to be used for both medical and industrial imaging.
Medical and industrial imaging: time taken for the reflections to reach a detector can be used to determine how far away such a boundary is.
Earthquakes produce seismic waves (S and P).
P-waves: longitudinal, seismic waves. P-waves travel at different speeds through solids and liquids.
S-waves are transverse, seismic waves. S-waves cannot travel through a liquid.
P-waves and S-waves provide evidence for the structure and size of the Earth’s core.
Echo sounding, using high frequency sound waves is used to detect objects in deep water and measure water depth.
Gamma rays originate from changes in the nucleus of an atom.
Changes in atoms and the nuclei of atoms can result in electromagnetic waves being generated or absorbed over a wide frequency range.
Lense:
Visible Light: each colour has a certain frequency and wavelength.
Specular reflection: reflection from a smooth surface in a single direction.
Diffuse reflection: reflection from a rough surface causes scattering.
Colour filters work by absorbing certain wavelengths (and colour) and transmitting other wavelengths (and colour).
If all wavelengths are reflected equally the object appears white. If all wavelengths are absorbed the objects appears black.
Objects that transmit light are either transparent or translucent.
All bodies emit and absorb infraredradiation. Hotter = more radiation.
A perfect black body is an object that absorbs all of the radiation incident on it. A black body does not reflect or transmit any radiation.
A good absorber is a good emitter, so a perfect black body would be the best possible emitter.
The temperature of a body increases when the body absorbs radiation faster than it emits radiation, and vice versa.