Properties of waves, including light and sound

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  • Created by: rachmhw
  • Created on: 11-04-19 15:41
what are waves?
they transfer energy without transferring matter
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examples of wave motions
light, sound, waves on water, waves in a spring
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what are the two ways waves are formed?
by vibrations either longitudinal or transverse
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describe features of longitudinal waves
backward and forward movements, have rarefaction and compression, vibrations parallel to energy transfer
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describe features of transverse wavse
sideways movements, energy travels perpendicular to movement
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exmaples of longitudinal waves
sound waves
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examples of transverse waves
light waves
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what does speed mean for waves?
the distance travelled by the wave in one second
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what does frequency mean for waves?
the number of waves passing a point in one second
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what does wavelength mean for waves?
the distance from one peak to the next
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what does amplitude mean for waves?
the maximum displacement from the equilibrium position
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in wave diagrams, what do the single lines showing the direction of the waves show?
the rays
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in wave diagrams, what do the parallel lines show?
the wavefronts
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how can you demonstrate the properties of a wave in an experiment?
using a ripple tank
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what do all waves do?
reflect, refract and diffract
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what is the law of reflection?
the angle of incidence is equal to the angle of relfection
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when do waves undergo reflection?
at a plane surface
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when do waves undergo refraction?
when they travel from one material to another
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why does refraction occur?
because the waves has changed speed in the materials causing a direction change
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what does not change during refraction?
frequency
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what changes during refraction? how?
wavelength decreases (when slowing down) or increases(when speeding up)
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what is diffraction?
when waves spread out as they pass through a narrow gap
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when does diffraction usually occur?
when the width of the gap is round the same size as the wavelength
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what is the equation for wavespeed?
v (m/s) = f (Hz) x wavelength (lamda, m)
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what is the normal line?
an imaginary line at 90 degrees to the surface
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how to we measure the incident and reflected ray?
from the normal line
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describe what an image is like in a plane mirror?
upright, laterally inverted, as far behind the mirror as the object is in front and virtual (the image isn't actually behind the mirror)
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what happens to the direction of the waves when it slows down?
it bends towards the normal
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what is the refractive index?
a number calculated to show how big an effect refraction has at a boundary between 2 materials
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how can you calculate the refractive index, n?
n= speed of light in a vacuum / speed of light in the material OR n= sin i / sin r
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what 2 things must be true for total internal reflection?
the angle of incidence must be greater than the critical angle AND the light must be passing from an optically more dense medium to a less dense medium
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what is the critical angle?
the angle at which the emergent ray exits with an angle of refraction of 90 degrees - along its boundary
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when does total internal reflection occur?
when the angle of incidence is increased further than the critical angle. the light reflects instead
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how can we calculate the reflective angle when light is at the critical angle?
use n = 1 / sin c
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what does total internal reflection allow?
light to be sent down optical fibres
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uses of opitcal fibres in medicine
endoscopes use optical fibres to direct light down the digestive tract in humans for examinations/ diagnostics without the need of surgery
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how are optical fibres used in homes?
it allows for coded information to be sent quickly and efficiently in fibre broadband internet connections
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what does a thin converging lens do to a beam of light?
it causes parallel rays of light to converge (come together) to a point called a principal focus
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what is another name for a converging lens?
convex or positive lens?
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what is the focal length?
the distance from the lens to the principal focal length
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what are the rules for drawing a ray diagram?
Draw object on principal axis, draw ray from top of object through centre of lens, draw a ray parallel from top to focus, draw rays from focus of the lens (in front of lens) parallel to axis, where all lines meet = position of image
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what can lens do the image?
enlarge, same size, diminish them / inverted or upright
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what happens when the object is closer than the principal focus?
the image is enlarged and lens acts as a magnifying glass / it is a virtual image
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what happens when white light is shone into a triangular prism?
the different colours change speed by different amounts and so they follow different paths = a spectrum of colours
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what are the 7 colours of the spectrum (in order)?
Red, orange, yellow, green, blue, indigo, violet (ROYGBIV)
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what is the name of spitting of light into the separate colours?
dispersion
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what is the name of light with a single wavelength?
it is monochromatic
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what is the electromagnetic spectrum?
a spectrum of waves
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what is the order of waves of the electromagnetic spectrum in increasing wavelength?
gamma rays, X-rays, ultra-violet, visible light, infra-red, micro-waves, ultra-high frequency, very high frequency, short-wave radio, medium-wave radio, long-wave radio
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how to these waves travel in a vacuum?
all at the same speed - 3.0 x 10^8 m/s (approximately the same in air)
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uses of radio waves?
communication - terrestrial TV signals and radio
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uses of microwaves?
mobile phone signals, cooking
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dangers of microwaves?
cause water molecules to vibrate with greater energy = heat up objects (e.g. humans)
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uses of infra-red waves?
remote controls, intruder alarms
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dangers of infra-red waves?
infra-red radiation is heat radiation = can burn
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uses of visible light waves?
communication
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uses of ultraviolet waves?
security marking
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dangers of ultraviolet waves?
can damage cells = skin cancer
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uses of X-ray waves?
medical imaging, security scanning (airports)
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dangers of X-ray waves?
can penetrate body and damage cells = cancer
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uses of gamma rays?
sterilising medical instruments, medical imaging, medical treatment
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danger of gamma rays?
can penetrate body and damage cells = cancer
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what causes sound?
vibrations
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how do sound waves travel?
as longitudinal pressure waves
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what do sound waves need for the vibrations to pass along?
a medium
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what can sound not travel through?
a vacuum
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what is the human range of audible frequencies for a healthy human ear?
20 Hz to 20 000 Hz
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what is the compression of sound waves?
when the waves passes through the medium, the particles are a little closer together than usual
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what is rarefaction of sound waves?
this is when the particles are a little bit further apart
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how can you measure the speed of sound with an experiment measuring distance between microphones and time difference?
distance between microphones / time difference between sound arriving
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typical value for speed of sound in steel (solid)?
3200 m/s
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typical value for speed of sound in water (liquid)?
1500 m/s
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typical value for speed of sound in air (gas)?
320 m/s
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what medium does sound travel best in? Why?
in a solid because the vibrations can go to one particle to another as they are very close
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what does a high pitch mean?
a high frequency
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what does a loud sound mean?
a large amplitude
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what is ultrasound?
frequencies above the range of human hearing
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what can cause echoes?
the reflection of sound
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examples of wave motions

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light, sound, waves on water, waves in a spring

Card 3

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what are the two ways waves are formed?

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Card 4

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describe features of longitudinal waves

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Card 5

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describe features of transverse wavse

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