Topic 2 - Waves and EM Spectrum Flashcards
what is a wave?
an oscillation that transfers energy without transferring any matter
transverse waves
oscillations are perpendicular to the direction of energy transfer
- they DON’T need a medium to travel through
examples of transverse waves
EM waves, ripples on water
longitudinal waves
oscillations are parallel to the direction of energy transfer
– they DO need a medium to travel through
examples of longitudinal waves
sound waves
amplitude
distance from the undisturbed position to the peak or trough
( maximum displacement )
wavelength
distance between the same point on two adjacent waves
frequency
number of waves passing a point per second (Hz)
period
amount of time it takes for a wave to pass a point (s)
period = 1 / frequency
wave speed
speed = wavelength x frequency
speed of sound in air
340 m/s
what 3 things can happen to a wave once it enters a different medium?
1) absorption
2) reflection
3) transmission ( refraction )
absorption
waves are absorbed by the material and energy is transferred to the material’s energy stores
reflection
the waves may bounce back
transmission
the waves keep on travelling through the new material but often undergo refraction
refraction
- when the speed of a wave changes as it crosses a boundary between 2 materials so
- changes direction if it hits the boundary at an angle ( not normal )
speed of waves in refraction
if it bends towards the normal it is moving slower
if it bends away from the normal it is moving faster
interpreting wavefronts
when the wavelength of the waves decreases it shows that the wave is moving more slowly, and so bending towards from the normal
how do sound waves travel?
- the particles vibrate from side to side
-parallel to the direction of wave travel - vibrations passing through the object passing on the energy
why does sound travel fastest in solids?
- solid is more dense so the particles are more closely packed together
- frequency of vibrations between particles will increase and so wave will travel faster through the material
what stays the same and what changes when a wave is refracted
frequency remains constant
wavelength changes
auditory range
20 Hz - 20kHz
how do ears detect sound? (P1)
- sound wave travel through ear canal
- causing eardrums to vibraet
- ossicles transmit these vibrations to the cochlea
how do ears detect sound? (P2)
- cochlea converts these into electrical signals
- passing through the auditory nerve into the brain where they are interpreted as sound
what is ultrasound?
sound waves with frequency above 20kHZ. they are partially reflected
industrial imaging - Ultrasound use
- used in industry to make sure objects aren’t faulty
- normally ultrasound waves will be refracted by the far end of object but
- if there is a crack then the ultrasound wave will be partially reflected and detected sooner
echo sounding
- used to find depth of water or locate submarine
- a pulse of ultrasound waves emitted and time taken for echo to return is noted
-helps us find depth of water
EM Waves
- group of transverse waves that transfer energy from source to absorber
order of EM waves ( increasing freq)
radio, microwave, infrared, visible light, UV, X-ray, gamma ray
uses of radio waves `
communication : radio and bluetooth
uses of microwaves `
satelite communication, cooking food
use of infrared
infrared cameras, cooking , electric heaters
use of visible light
vision, fibre optic cables
use of UV
sun tanning , energy efficient lamps
use of X-ray
visualise broken bones
use of gamma ray
sterilising medical objects
radiotherapy
dangers of UV, X-ray and Gamma
they are all high frequency which means they carry lot of energy and can cause damage to cells
dangers of UV
damages skin and causes sunburns
can cause skin cancer
dangers of X-rays and gamma rays
ionising radiation
ability to knock electrons off atoms
destroys cells and causes gene mutation
leads to cancer
seismic waves
produced by earthquakes and carry energy away from earthquakes’s epicenter
seismic P
longitudinal
pass through solids and liquids
seismic S
transverse
only pass through solid
using seismic S waves to investigate earth’s structure
can’t detect S waves on other side of earth because some of earth’s structure is a liquid ( core )
using seismic P waves to investigate earth’s structure
