Unit 6 - Waves Flashcards
What are the two types of waves
-transverse (ripples on water )
-longitudinal (sound waves)
What is amplitude
Maximum displacement of a point on the wave from its undisturbed position
What is the wavelength
Distance between the same point on two adjacent waves (between the trough of one wave and the trough of the wave next to it )
What is the trough and crest
Trough = lowest point
Crest = highest point
What is frequency of waves
-Number of complete waves passing a certain point per second
-measured in hertz
-1 hz is one wave per second
What do waves do
-transfer energy in the direction they are travelling
-when waves travel through a medium, the particles of the medium oscillate and transfer energy between each other
What does oscillate mean
Vibrations or movements
What are transverse waves
-when the oscillations are perpendicular to the direction of energy transfer
-most waves are transverse including all electromagnetic waves, ripples in water and wave on a string
What are longitudinal waves
-oscillation are parallel to the direction of energy transfer
-if you push the end of a spring you get a longitudinal wave
For equation wave speed = frequency x wave length what are the units for all of them
Wave speed = m/s
Wavelength = m
Frequency = Hz (hertz )
Describe a method to measure the speed of sound waves in air
-set up oscilloscope so the detected waves at each microphone are shown as separate waves
-start with both microphones next to the speaker then slowly move one away until the two waves are aligned on the display but have moved exactly one wavelength apart
-measure the distance between the microphones to find on wavelength
-then use formula wave speed = frequency x wavelength to find speed of sound waves passing through the air
How to calculate wavelength of standing wave
Divide total length by the number of half wavelengths and then you multiply by 2
How are changes in velocity, frequency and wavelength in transmission of sound waves interrelated
-frequency remains unchanged
-velocity changes depending on medium properties (solid or gas)
-wavelength changes proportionally to velocity
What can all waves do (be a_________, t__________ or r__________)
Absorbed, transmitted or reflected
What does transmitted mean
-The waves carry on travelling through the new material
-this often leads to refractment
What does it mean when waves are absorbed
-this means there is a transfer of energy to the materials energy stores
Equation to learn for all reflected waves
Angle of incidence = angle of reflection
What is the angle of incidence
The angle between the incoming wave and the normal line
What is the normal line
-Imaginary line perpendicular to the surface at the point of incidence
-usually shown as dotted line
What is a specular reflection
-happens when a wave is reflected in a single direction by a smooth surface
-e,g when light is reflected by a mirror you get a nice clear reflection
What is a diffuse reflection
-when a wave is reflected by a rough surface (piece of paper) the reflected rays are scattered in lots of different directions
-this happens because the normal line is different for each incoming ray which means that angle of incidence is different for each ray
-when light is reflected by rough surface the surface appears matte and you don’t get clear reflection of object
What is refraction
-waves changing direction at a boundary
-if a light wave hits the boundary face on it carries on in the same direction
-if a wave meets a different medium at an angle the wave changes direction and its refracted
-how much it’s refracted depends on density of the two materials
-the higher the density the slower a wave will travel which will bend it towards the normal line
-if the wave speeds up it will bend away from the normal line
How to construct refraction ray diagram
-draw boundary between 2 materials and the normal line
-draw an incident ray that meets the normal line and label angle of incidence
-draw refracted ray on other side of boundary
-if density increases then angle between normal and refracted ray is smaller than angle of incidence if density decreases then a angle of refraction is bigger
What is a period of a wave
Time taken for a full wave to pass a point
What are electromagnetic waves and name them all
-transverse waves that transfer energy from source of waves to the absorber
-form a continuous spectrum and all types of EM waves travel at same velocity through a vacuum (space ) or air
-the waves that form the spectrum are grouped in terms of their wavelength and their frequency
-going from long to short wavelength (or low to high frequency)
-the order is : radio, micro, infrared, visible, ultraviolet, X rays and gamma rays
-our eyes only detect visible light
Properties of radio waves
-Can be produced by oscillations in electrical circuits
-when radio waves are absorbed they may create an alternating current with the same frequency as the radio wave itself
-this is because the energy transferred by wave is transferred to the electrons in the material of the receiver this energy causes the electrons to oscillate and if part of a complete circuit it generates an alternating current
What are gamma rays
-they originate from changes in the nucleus of an atom
Uses of radio waves
-Used for communications
-transmitted through air easily (can bend around / pass through objects
-don’t cause damage if absorbed by body
-can be reflected to change their direction
-used tv and radio
Uses of microwaves
-used by satellites for communication to and from
-can easily pass through earths watery atmosphere
-used in cooking in microwave ovens where microwaves are absorbed by water molecules in food
-penetrate into food, energy they are carrying causes water to heat up
-water molecules transfer energy which cooks food
Uses of infrared
-infrared cameras can be used to detect infrared radiation and monitor temperature
-food can be cooked by infrared, the temperature of food increases when it absorbs IR
Uses of ultraviolet rays
-produced by sun and exposure to it is what gives people a sun tan
-overexposure can be dangerous
-energy efficient lamps (fluorescent lamps)
Uses of visible light
-used in communications
-fibre optic cables use visible light to transmit data
-they work because of reflection as the light rays bounce back and forth until they reach end of fibre
Uses of X-rays and gamma rays
-used in medical imaging and treatments
-X rays pass easily through flesh but not so easily through denser material like bones
-gamma rays can be injected into patient and the gamma rays emitted are detected by external detector. By seeing where the gamma rays come from:they can track progress of tracer around body and check it is functioning correctly
-both can be harmful so radiographers were lead aprons or leave the room
Dangers of EM waves
-damage depends on how much energy the wave transfers
-high frequency waves like UV, X rays and gamma ways all transfer lots of energy so can cause damage
Dangers of UV radiation
-damages surface cells which can lead to sunburn
-can cause skin to age prematurely
-increase the risk of skin cancer
Dangers of X-rays and gamma rays
-ionising radiation that can cause mutation of genes and cancer
What do you measure the risk of radiation dose in
Sieverts
Explain how TV satellites are transmitted from transmitter on the ground to a house
-transmitted through atmosphere into space where they are picked up by a satellite receiver orbiting Earth
-the satellite transmits the signal back to Earth in a different direction where it is received by a satellite dish connected to the house
What are seismic waves and what did they do
-earthquakes and explosions cause seismic waves
-waves can follow curved paths which show density of material of earth changing, suggesting areas of earths inner structure made up of similar material of density, when waves suddenly change direction it shows density has changed a lot which means they have entered a new layer of the earths structure
What are P-waves
-are longitudinal seismic waves
-travel at different speeds through solid and liquids
-travel faster than S. waves
What are S-waves
-transverse seismic waves
-cannot travel through a liquid
-so lower than P-waves
How are lenses formed
-Form an image by refracting light
-there are 2 types concave and convex
What happens in a convex lens
-parallel rays of light come together (converge) to focus at a principal focus
What happens in concave lens
-causes rays of light to diverge
-the principal focus of a concave lens is the point the rays hitting the lens parallel to the axis appear to all come from
What is the focal length
Distance from centre of lens to principal focus
2 rules for convex lens (can use these for ray diagrams)
-an incipient ray parallel to the axis refracts through the lens and passes through the principal focus on the other side
-an incident ray passing throng the centre of the lens carries on in the same direction
2 rules for concave lenses
-incident ray parallel to the axis refracts through the lens and travels in line with the principal focus
-an incident ray passing through the centre of the lens carries on in the same direction
Difference between real and virtual images
-a real image is where the light from an object comes together to form an image on a screen
-convex can be real or virtual
-virtual image is when rays are diverging so the light from the object appears to be coming from completely different places
-concave lens is always virtual
3 things to say to describe an image
-whether it’s real or virtual
-whether it’s magnified or diminished (is the image length/ arrow longer or shorter than the object length/ arrow)
-whether it’s upright or inverted (is the image upside down or upright)
How to draw a ray diagram for a convex lens
-draw a line parallel to the axis from the top of the object to the lens
-draw another ray from the top of the object going right through the middle of the lens
-the incident ray that’s parallel to the axis refracts through the principal focus on the other side of the lens
-the ray passing through the middle of the lens does not bend
-mark where the rays meet, this is the top of the image
How to draw a ray diagram for a concave lens
-draw a ray going parallel to the axis to the lens from the top of the object
-draw another ray from the top of the object going right through the middle of the lens
-the incident ray that’s parallel to the axis refracts so that it appears to come from the principal focus
-the ray passing through the middle does not bend
Magnification equation
Image height / object height
-make sure units are the same
What are opaque objects and what do the colour we see depend on
-Do not transmit light, when visible light hits them they absorb some wavelengths of light and reflect others
Fill in the gaps : each colour with the visible light spectrum has its down narrow band of ____________ and _________
Wavelength , frequency
what do the colour we see depend on for primary colours
-the colour of an opaque object depends on which wavelengths of light are most strongly reflected
-(red apple has a combination of colours hit it but red light is strongly reflected and all other colours are absorbed)
What do the colours we see depend on (if they are not a primary colour)
-they may be reflecting either the wavelengths of light corresponding to make that colour or the wavelengths of primary colours that mix together to make that colour
-for example a banana may be reflecting yellow light or because it’s reflecting both green and red
What do black and white objects do
-black objects absorb all wavelengths of visible light so our eyes see a lack of any visible light
-white objects reflect all wavelengths of visible light
How do colour filters work
-absorb certain wavelengths and colour and transmitting other wavelengths and colour
-primary colour filter only transmits that colour
-non primary colour filters let through bight wavelengths of light for that colour and wavelengths of primary colours that can be added to make that colour
What do transparent and translucent objects do
-some wavelengths of light may be absorbed or reflected by them
-it’s colour is related to the wavelengths of light transmitted and reflected by it
What are the primary colours and what colours do they make
-green + red+ blue = white
-green + red = yellow
-green + blue = cyan
-red + blue= magenta
-red + green = yellow
-yellow + cyan = green
-cyan + magenta = blue
-magenta + yellow = red
What is infrared radiation
-all bodies no matter what temperature emit and absorb infrared radiation
-the hotter the body the more infrared radiation it radiates in a given time
Fill in the gaps the intensity and ____________ distribution depends on the __________ of the body
Wavelength, temperature
Note = as the temperature of an object increases the intensity of every emitted wavelength increases
What is a perfect black body
-An object that absorbs all of the radiation that hits it, no radiation is reflected or transmitted
-since a good absorber is also a good emitter a perfect black body would be the best possible emitter
What does temperature of Earth depend on
-rates of absorption and emission of radiation
-reflection of radiation into space
-for example at night less radiation is being absorbed than is being emitted causing a decrease in temperature
-in the day lost of radiation like light is being transferred to the earth from the sun this causes an increase in temperature
-some radiation is absorbed by atmosphere, clouds and earths surface
What are sound waves and how do they work in the ear
-can’t travel in space because it’s mostly a vacuum (no particles to move or vibrate)
-longitudinal wave
-can travel through solid causing vibrations in solid (travels fastest in solids )
-they travel through air as a series of compressions and rarefactions
-sound waves cause the ear drum and other parts to vibrate which causes the sensation of sound
-conversion of sound waves to vibrations of solid works over a limited frequency range, this restricts the limits of human
hearing
-normal human hearing range is 20Hz to 20kHz
What is ultrasound waves
-sound with frequency higher than the upper limit for humans
-they are partially reflected when they meet a boundary between 2 different media
-the time taken for a reflection to reach a detector can be used to determine how far away such boundary is
Uses of ultra sound
-used in medical and industrial imaging
-ultrasound imaging creates a picture of something that cannot be seen directly such as an unborn baby
