Wave Properties

The Nature of Waves

- waves can be used to transfer energy and information

- transverse waves oscillate perpendicular to the direction of energy transfer of the waves, ripples on the surface of water are transverse waves, so are all electromagnetic waves

- longitudinal waves oscillate parallel to the direction of energy transfer of the waves, sound waves in air are longitudinal waves

- mechanical waves need a medium (a substance) to travel through, they can be transverse or longitudinal

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Properties of Waves

- for any wave, its amplitude is the maximum displacement of a point on the wave from its undisturbed position, such as the height of the wave crest (or the depth of the wave trough) from the position at rest

- for any wave, its frequency is the number of waves passing a point per second

- the period of a wave = 1 / frequency

- for any wave, its wavelength is the distance from a point on the wave to the equivalent point on the next wave (e.g. from one wave trough to the next wave trough)

- speed of a wave is:

    speed = frequency x wavelength

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Reflection and Refraction

- plane waves in a ripple tank are reflected from a straight barrier at the same angle to the barrier as the incident waves because their speed and wavelength do not change on reflection

- plane waves crossing a boundary bewteen 2 different materials are refracted unless they cross the boundary at normal incidence 

- refraction occurs at a boundary between 2 different materials because the speed and wavelength of the the waves change at the boundary

- at a boundary between 2 different materials, waves can be transmitted or absorbed

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More About Waves

- sound waves are vibrations that travel through a medium (a substance)

- sound waves cannot travel through a vaccum (e.g. in outer space)

- to investigate waves, use:

    > a ripple tank for water waves

    > a stretched string for waves in a solid

    > a signal generator and a loudspeaker for sound waves

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Sound Waves

- the pitch of a note increases if the frequency of a sound waves, if the frequency of the sound waves increases

- the loudness of a note increases if the amplitude of the sound waves increases

- sound waves cause the ear drum to vibrate and the vibrations send signals to the brain

- the conversion of sound waves to vibrations of solid only works over a limited frequency range, so human hearing is limited

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Uses of Ultrasound

- ultrasound waves are sound waves of frequency above 20kHz

- ultrasound waves are partly reflected at a boundary between 2 different types of body tissue

- ultrasound waves are reflected at boundaries are timed and the timings are used to calculate distances

- an ultrasound scan is non-ionising, so it is safer than an x-ray

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Seismic Waves

- seismic waves are waves that travel through the Earth

- seismic waves are produced in an earthquake and spread out from the epicentre

- primary seismic waves (P-waves) are longitudinal waves, secondary seismic wave (S-waves) are transverse waves

- the Earth has a solid inner core surrounded by a liquid outer core, which is surrounded by the Earth's mantle, the mantle is surrounded by the Earths crust

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