waves Flashcards
transfer of energy through waves
- waves consist of a pattern of vibrations (oscillations).
- when the wave is absorbed it transfers energy to the object that absorbs it, but there is no transfer of matter
types of waves
- transverse waves: vibration direction is perpendicular to wave direction
- e.g. all EM spectrum waves
- longitudinal waves: vibration direction is parallel to wave direction
- e.g. sound waves, ultrasound waves
crest
top of the wave
trough
bottom of the wave
amplitude
- half the height of the wave
- a measure of how much energy the wave has
- symbol: A
- units: metres
wavelength
- distance of one wave (from one crest to the next crest in transverse waves, distance between adjacent compressions/rarefactions in longitudinal waves)
- symbol: upside down Y (lamda)
- units: metres
frequency
- number of waves produced in one second
- symbol: f
units: Hz
period
- time taken to produce one wave
- symbol: T
- units: seconds
speed
- distance travelled by wave in one second
- symbol: v
- units: ms-1
formulae (3)
v = f x lamda f = N/t T = 1/f
compressions and rarefactions
- the pattern of vibration for longitudinal waves
- compression: particles in the medium are pushed closer together as the wave passes (lines close together)
- rarefaction: particles in the medium are pulled further apart as the wave passes (lines further apart)
- distance between 2 adjacent compressions or 2 adjacent rarefactions = 1 wavelength
mechanical waves
-consist of vibrating particles, so can only move through a material medium (can’t travel through a vacuum)
electromagnetic waves properties
- don’t need a material medium, so they travel through a vacuum
- they always travel at the speed of light (3x10^8 ms-1) in a vacuum and air
EM waves types
- Radio: ROGER (longest wavelength, lowest frequency)
- Microwave: MOORE
- Infra-red: INVENTS
- Visible light: VERY
- Ultra-violet: USEFUL
- X-ray: XBOX
- Gamma-ray: GAMES (shortest wavelength, highest f)
mechanical waves types
- Sound
- Ultrasound
- Seismic waves: longitudinal and transverse vibrations of matter inside the Earth travelling outwards from earthquakes
- Water waves: partly traverse, partly longitudinal
- Waves on a string
prefixes
milli: 10^−3
micro: 10^−6
nano: 10^−9
kilo: 10^3
mega: 10^6
giga: 10^9
refraction
- the change of speed of light waves when light enters a new medium
- incidence angle (i) angle between the normal and the incident ray
- reflected angle (r) angle between the normal and the reflected ray
- incidence ray=reflected ray
- normal=line drawn perpendicular to the surface at a point where the ray hits the surface
reflection from smooth and rough surfaces
- if the surface is smooth all the normals are parallel to one another so all the waves are reflected in an orderly way
- if the surface is rough the normals at each point are in different directions so each ray is reflected in a random direction
refraction in different media
- when waves enter a more dense medium, it slows down and refracts toward the normal (e.g. air to glass).
- when waves enter a less dense medium, it speeds up it and refracts away from the normal (e.g. glass to air)
- when leaving the object, the ray is parallel to the ray entering the object
reflection affect on frequency, wavelength, speed and direction
- reflection changes the direction of a wave
- reflection doesn’t change its speed, frequency and wavelength because the reflected wave remains in the same medium
refraction affect on frequency, wavelength, speed and direction
- refraction involves a change of wave speed
- increasing wave speed (entering a less dense medium) increases wavelength
- decreasing wave speed (entering a denser medium) decreases wavelength
- frequency is unchanged
- the direction of the wave changes unless the incident wave is travelling along the normal to the boundary
- the greater the change in speed, the larger the refraction
Doppler effect
- source and observer at rest relative to one another: no change on wavelength or frequency
- source and observer approaching one another: shorter wavelength, higher frequency
- source and observer moving away from one another: longer wavelength, lower frequency
Relationship between vibrations of source and sound produced
- the sound waves have the same frequency as the vibrations of the source
- the amplitude of the sound waves depends on the amplitude of the vibrations of the source
- the speed of the sound waves is determined by the medium through which they travel (not by the source)
ultrasound vs sound
- sound has frequencies within the limit of human hearing ( < 20kHz)
- ultrasound has frequencies above the limit of human hearing ( > 20kHz)
loudness of a sound
- depends on the amplitude of the sound waves
- the greater the amplitude, the louder the sound
pitch of a sound
- depends on the frequency of the sound waves
- the higher the frequency, the higher the pitch
using sound reflection (echoes) to measure distance
𝑑=𝑣𝑡/2
range of human hearing
-the human ear cannot detect sounds with frequencies <20 Hz or >20 kHz
visible light
Visible light is subdivided into 7 regions:
- red: RICHARD (longest wavelength, lowest frequency)
- orange: OF
- yellow: YORK
- green: GAVE
- blue: BATTLE
- indigo: IN
- violet: VAIN (shortest wavelength, highest frequency)
X rays and gamma rays
- X-rays are usually produced when fast moving electrons crash into a metal target and stop
- Gamma-rays are usually produced by radioactive decay
- X-rays and gamma-rays with the same wavelength are identical
use of ultrasound
prenatal scanning
use of infrared light
thermal imaging
polarisation
- when the vibrations of a transverse wave are restricted to one direction
- all EM waves can be polarised
sound waves entering a denser medium
- speed increases
- wave refracts away from the normal
