P12 Wave Properties Flashcards
what are mechanical waves
and give examples
waves that travel through a medium
and can be transverse or longitudinal
e.g. sound waves, water waves, seismic waves
what are electromagnetic waves
and give examples
waves which travel through a vacuum at 300,000km per second
and are transverse
e.g. light waves, radio waves, microwaves
describe the oscillations of transverse waves
perpendicular to the direction of energy transfer
describe the oscillations of longitudinal waves
parallel to the direction of energy transfer
what is the amplitude of a wave
its maximum displacement from a point of rest
the larger the amplitude of a wave…
the larger the amplitude of a wave
the more energy the waves carry
what is the frequency of waves
and unit
the number of waves passing over a fixed point every second
Hz
what is the period of a wave
and unit
the amount of time it takes for each wave to pass a fixed point
in seconds
v = f λ
what unit is wavelength in
λ is in metres
how to calculate speed of sound in air
person A stands at a fixed, measured distance from person B,
A bangs cymbals,
using a stopwatch B times the interval between seeing and hearing the impact of the cymbals,
repeat 3x and calculate a mean time interval in seconds,
substitute values into speed (m/s) = distance (m) / time (s)
what is the refraction of a wave
the change of a wave’s direction when crossing the boundary between one medium and another
when an incident wave is refracted, which of these change:
- wavelength,
- frequency,
- speed.
frequency stays the same
but speed changes
which causes wavelength to change too.
whether a wave is reflected by a surface depends on:
- its wavelength,
- the material of the surface.
what happens to a substance when it absorbs waves?
it heats up
because gains energy from the waves
what happens to the amplitude of a wave as it travels through a substance
and why?
it gradually decreases
because the substance gradually absorbs some of the substance’s energy
what happens to waves that pass through a substance but are not absorbed?
they are transmitted
describe how humans hear sound
and why human hearing is limited
- sound waves vibrate the ear drum,
- causing the sensation of sound,
- but this only works over a limited frequency range,
- so outside this range humans cannot hear sounds.
how does a loudspeaker produce sound waves?
- it pushes surrounding air backwards and forwards,
- producing sound waves.
equation for calculating the speed of sound in air
a = 2d/t
increased amplitude means that a sound wave sounds…
louder
range of normal human hearing
20 Hz to 20 kHz
define ‘echo’
the reflection of sound waves from a smooth surface
what is echo sounding
using pulses of high frequency sound to detect objects in deep water and measure water depth below a ship
describe the process of echo sounding
- transmitter releases pulses of high frequency sound waves,
- which are reflected at the sea bed,
- back up to a receiver at an equal depth to the transmitter,
- s (twice the depth of the seabed) = v (speed of sound in water) x t (time taken for waves to be emitted then reflected back),
- so depth of water = 1/2 s = 1/2vt
what is the frequency of ultrasound waves
over 20kHz
how do ultrasound waves show how far away a boundary is
- ultrasound waves are partially reflected when they meet a boundary between 2 media,
- the time taken for waves to reach a receiver again can be used to determine how far away the boundary is from it.
uses of ultrasound waves
medical imaging
industrial imaging
advantages of ultrasound waves rather than X rays for medical imaging
- non-ionising, so harmless,
- reflect at boundaries between different media so can be used to scan organs and soft tissues.
2 main types of seismic wave
P (primary) waves
S (secondary) waves
compare P and S waves
P waves
- longitudinal seismic waves,
- travel through solids and liquids at different speeds,
S waves
- transverse seismic waves,
- cannot travel through liquids.
