Physics - Topic 6 - Waves

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  • Created by: hannah.o
  • Created on: 12-02-18 10:02
What do waves transfer?
They transfer energy in the direction they are travelling.
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What is the amplitude of a wave?
The maximum displacement of a point on the wave from its undisturbed position.
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What is the wavelength?
It is the distance between the same point on two adjacent waves.
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What is frequency?
It is the number of complete waves passing a certain point per second. Frequency is measured in hertz (Hz). 1Hz is 1 wave per second.
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What is the equation for period?
Period (s) = 1 / Frequency (Hz)
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What is period?
The amount of time it takes for a full cycle of the wave.
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What does a wave graph look like?
.
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What are the oscillations of a transverse wave?
The oscillations are perpendicular to the direction of energy transfer.
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What does this look like on a spring?
.
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What waves are transverse?
Most waves are transverse, including: all electromagnetic waves, ripples and waves in water, a wave on a string.
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What are the oscillations of a longitudinal wave?
The oscillations are parallel to the direction of energy transfer.
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What does this look like on a spring?
.
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What waves are longitudinal?
Sound waves in air, ultrasound and shock waves.
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What is wave speed?
The wave speed is the speed at which energy is being transferred (or the speed the wave is moving at).
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What is the wave equation?
Wave speed (m/s) = Frequency (Hz) x Wavelength (m)
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What is the speed of sound in air?
330m/s
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When waves arrive at a boundary between two different materials, what three things happen?
1)The waves are absorbed by material wave is trying to cross into-this transfers energy to the material's energy stores. 2)The waves are transmitted-waves carry on travelling through new material, often leads to refraction. 3)The waves are reflected.
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What is the rule for all reflected waves?`
Angle of incidence = Angle of reflection
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What is the angle of incidence?
It is the angle between the incoming wave and the normal.
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What is the angle of reflection?
It is the angle between the reflected wave and the normal.
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When does specular reflection happen?
Specular reflection happens when a wave is reflected in a single direction by a smooth surface.
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What does specular reflection look like?
.
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What is diffuse reflection?
Diffuse reflection is when a wave is reflected by a rough surface and the reflected rays are scattered in lots of different directions.
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What does diffuse reflection look like?
.
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Why does diffuse reflection happen?
Because the normal is different for each incoming ray, which means that the angle of incidence is different for each ray.
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When light is reflected by a rouch surface, what does the surface appear like?
The surface appears matte and you don't get a clear reflection of objects.
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What does the electromagnetic spectrum look like?
.
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What is refraction?
Waves changing direction at a boundary.
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What does refraction look like at normal through a different density?
.
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What does refraction look like at an angle through a different density?
.
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What happens to the light waves when the density is higher?
The higher the optical density, the slower light waves travel through it.
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How do you construct a ray diagram for a refracted light ray?
1) Draw the boundary between your two materials and the normal. 2) Draw an incident ray that meets the normal at the boundary. The angle between the ray and the normal is the angle of incidence.
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3) Now draw refracted ray on other side of boundary. If second material is optically denser than first, refracted ray and normal is smaller than angle of incidence. If second material is less optically dense, angle of refraction is larger.
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What does this look like?
.
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What are EM waves made up of?
Oscillating electric and magnetic fields.
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What are alternating currents made up of?
Oscillating charges. As the charges oscillate, they produce oscillating electric and magnetic fields, i.e. EM waves.
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What will the frequency of the waves produced be equal to?
The frequency of the waves produced will be equal to the frequency of the alternating current.
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How can you produce radio waves? (2)
Using an alternating current in an electrical circuit. The object in which charges oscillate to create the radio waves is called a transmitter. When transmitted radio waves reach a receiver, the radio waves are absorbed.
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The energy carried by the waves is transferred to the electrons in the material of the receiver.
This energy causes the electrons to oscillate and, if the receiver is part of a complete electrical circuit, it generates an ac. This current has the same frequency as the radio wave that generated it.
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What are radio waves?
Radio waves are EM radiation with wavelengths longer than about 10cm.
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Why can long-wave radio (wavelengths of 1-10km) be transmitted halfway round the world?
Because long wavelengths diffract (bend) around the curved surface of the Earth. This makes it possible for radio signals to be received even if the receiver isn't in line of sight of the transmitter.
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Why can short-wave radio signals (wavelengths of 10m-100m) be received at long distances from the transmitter?
Because they are reflected from the ionosphere - an electrically charged layer in the Earth's upper atmosphere.
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Which radio waves does Bluetooth use?
It uses short-wave radio waves to send data over short distances between devices without wires.
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What radio waves are used for TV and FM radio transmissions?
Very short wavelengths. To get reception, you must be in direct sight of the transmitter - the signal doesn't bend or travel far through buildings.
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What are microwaves used for?
Communication to and from satellites (including satellite TV signals and satellite phones).
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How do satellite TVs work?
The signal from a transmitter is transmitted into space where it's picked up by the satellite receiver dish orbiting thousands of kilometres above the Earth. The satellite transmits the signal back to Earth in a different direction where it's
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received by a satellite dish on the ground. There is a slight time delay between the signal being sent and received because of the long distance the signal has to travel.
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Where else are microwaves used?
In microwave ovens.
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What happens in microwave ovens?
The microwaves need to be absorbed by water molecules in food-so they use a different wavelength to those used in satellite communications. The microwaves penetrate up to a few centimetres into the food before being absorbed and transferring the
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energy they are carrying to the water molecules in the food, causing the water to heat up. The water molecules then transfer this energy to the rest of the molecules in the food by heating-which quickly cooks the food.
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What is infrared radiation?
IR radiation is given out by all hot objects - the hotter the object, the more IR radiation it gives out.
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What can infrared cameras be used for?
Infrared cameras can be used to detect IR radiation and monitor temperature. The camera detects the IR radiation and turns it into an electrical signal, which is displayed on a screen as a picture. The hotter an object is, the brighter it appears.
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What does absorbing IR radiation cause?
It causes objects to get hotter. Food can be cooked using IR radiation - the temperature of the food increases when absorbs IR radiation.
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How do electric heaters work in the same way?
Contain a long piece of wire that heats up when current flows through. This wire emits lots of IR radiation. Emitted IR radiation is absorbed by objects and air in room-energy is transferred by IR waves to thermal energy stores, causing temps to rise
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What are optical fibres?
Optical fibres are thin glass or plastic fibres that can carry data over long distances as pulses of visible light.
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Why do optical fibres work?
They work because of reflection. The light rays are bounced back and forth until they reach the end of the fibre.
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Which part of the EM spectrum is used in optical fibres?
Visible light
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Why is light used in optical fibres?
Because light is not easily absorbed or scattered as it travels along a fibre.
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What is fluorescence?
Fluorescence is a property of certain chemicals, where UV radiation is absorbed and then visible light is emitted.
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What do fluorescent lights generate?
They generate UV radiation, which is absorbed and re-emitted as visible light by a layer of phosphorus on the inside of the bulb. They're energy-efficient so they're good to use when light is needed for long periods.
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What can security pens be used to do?
They can be used to mark property with your name. Under UV light the ink will glow, but it's invisible otherwise. This can help the police identify your property if it's stolen.
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What produces UV radiation?
The Sun, and exposure to it is what gives people a suntan.
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What do X-rays do?
They easily pass through flesh but not so easily through denser material like bones or metal. So it's the amount of radiation that's absorbed that gives you an X-ray image.
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How can radiographers treat people with cancer?
They use X-rays and gamma rays. This is because high doses of these rays kill all living cells - so they are carefully directed towards cancer cells, to avoid killing too many normal, healthy cells.
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What can gamma radiation be used as?
A medical tracer-this is where a gamma-emitting source is injected into the patient, and its progress is followed around the body. Gamma radiation is well suited to this because it can pass out through the body to be detected.
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What do radiographers do for their safety?
They wear lead aprons and stand behind a lead screen or leave the room to keep their exposure to them to a minimum.
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What do low frequency waves do?
Low frequency waves, like radio waves, don't transfer much energy and so mostly pass through soft tissue without being absorbed.
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What do high frequency waves do?
High frequency waves like UV, X-rays and gamma rays all transfer lots of energy and so can cause lots of damage.
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How is UV radiation dangerous?
UV radiation damages surface cells, which can lead to sunburn and cause skin to age prematurely. Some more serious effects are blindness and an increased risk of skin cancer.
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How are X-rays and gamma rays dangerous?
They are types of ionising radiation (they carry enough energy to knock electrons off of atoms). This can cause gene mutation or cell destruction, and cancer.
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How do lenses form images?
Lenses form images by refracting light and changing its direction.
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What do convex lenses do?
A convex lens bulges outwards. It causes rays of light parallel to the axis to be brought together (converge) at the principal focus.
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What do concave lenses do?
A concave lens caves inwards. It causes parallel rays of light to spread out (diverge).
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What is the axis of a lens?
It is a line passing through the middle of the lens.
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What is the principal focus of a convex lens?
It is where rays hitting the lens parallel to the axis all meet.
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What is the principal focus of a concave lens?
It is the point where rays hitting the lens parallel to the axis appear to all come from.
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What does a convex lens ray diagram look like?
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What does a concave lens ray diagram look like?
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What are the 3 rules for refraction in a convex lens?
1) An incident ray parallel to the axis refracts through the lens and passes through the principal focus on the other side. 2) An incident ray passing through the principal focus refracts through the lens and travels parallel to the axis.
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3) An incident ray passing through the centre of the lens carries on in the same direction.
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What are the 3 rules for refraction in a concave lens?
1) An incident ray parallel to the axis refracts through the lens, and travels in line with the principal focus. 2) An incident ray passing through the lens towards the principal focus refracts through the lens and travels parallel to the axis.
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3) An incident ray passing through the centre of the lens carries on in the same direction.
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What is a real image?
A real image is where the light from an object comes together to form an image on a 'screen' - like the image formed on an eye's retina.
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What is a virtual image?
A virtual image is when the rays are diverging, so the light from the object appears to be coming from a completely different place.
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What are the 3 things you need to say to describe an image properly?
1) How big it is compared to the object. 2) Whether it's upright or inverted relative to the object. 3) Whether it's real or virtual.
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How do you draw a ray diagram for an image through a convex lens? (2)
1) Draw a ray going from the top of the object to the lens parallel to the axis of the lens. 2) Draw another ray from the top of the object going right through the middle of the lens.
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3) The incident ray that's parallel to the axis is refracted through the pincipal focus (F) on the other side of the lens. Draw a refracted ray passing through the principal focus. 4) The ray passing through the middle of the lens doesn't bend.
5) Mark where the rays meet. This is the top of the image. 6) Repeat the process for a point on the bottom of the object. When the bottom of the object is on the axis, the bottom of the image is also on the axis.
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What image will an object at 2F produce?
A real, inverted image the same size as the object and at 2F.
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What image will an object between F and 2F produce?
A real, inverted image bigger than the object, and beyond 2F.
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What image will an object nearer to the axis than F produce?
A virtual image the right way up, bigger than the object and on the same side of the lens.
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How do you draw a ray diagram for an image through a concave lens? (2)
1) Draw a ray going from the top of the object to the lens parallel to the axis of the lens. 2) Draw another ray from the top of the object going right through the middle of the lens.
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3) The incident ray that's parallel to the axis is refracted so it appears to have come from the principal focus. Draw a ray from the principal focus. Make it dotted before it reaches the lens. 4) The ray passing through the middle of the lens
doesn't bend. 5) Mark where the refracted rays meet. This is the top of the image. 6) Repeat the process for a point on the bottom of the object. When the bottom of the object is on the axis, the bottom of hte image is also on the axis.
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How do magnifying glasses work?
By creating a magnified virtual image.
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What is the equation for magnification?
Magnification = image height / object height
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What are the primary colours?
Red, green and blue.
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What do opaque objects do?
They do not transmit light. When visible light waves hit them, they absorb some wavelengths of light and reflect others.
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What does the colour of an opaque object depend on?
It depends on which wavelengths of light are most strongly reflected.
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What do white objects do?
They reflect all wavelengths of visible light equally.
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What do black objects do?
They absorb all wavelengths of visible light.
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What do transparent and translucent objects do?
They transmit light.
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What are colour filters used to do?
To filter out different wavelengths of light, so that only certain colours are transmitted - the rest are absorbed.
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What colours does a primary colour filter transmit?
It only transmits its own colour.
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What colours do filters that aren't primary colours transmit?
They let through both the wavelengths of light for that colour and the wavelengths of the primary colours that can be added together to make that colour.
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Which surface is better at absorbing and emitting radiation?
Black rather than white. Matt rather than shiny.
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What is a perfect black body?
An object that absorbs all of the radiation that hits it. No radiation is reflected or transmitted. They are the best possible emitters of radiation.
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What 2 things depend on the object's temperature?
Intensity and distribution of the wavelengths emitted by an object.
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What happens as the temperature increases?
As the temperature of an object increases, the intensity of every emitted wavelength increases.
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When does the intensity increase more rapidly?
The intensity increases more rapidly for shorter wavelengths than longer wavelengths. This causes the peak wavelength to decrease.
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What does this look like on a graph?
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What does the temperature of the Earth depend on?
The amount of radiation it reflects, absorbs and emits.
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What are sound waves caused by?
Vibrating objects. These vibrations are passed through the surrounding medium as a series of compressions and rarefactions.
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When does sound travel faster?
Sound travels faster in solids than in liquids, and faster in liquids than in gases.
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Show how sound travels through air and a solid object.
.
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What is ultrasound?
Sound with frequencies higher than 20,000Hz.
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What happens when a wave passes from one medium into another?
Some of the wave is reflected off the boundary between the two media, and some is transmitted (and refracted). This is partial reflection. This means you can point a pulse of ultrasound at an object, and wherever there are boundaries between one
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substance and another, some of the ultrasound gets reflected back. The time it takes for the reflections to reach a detector can be used to measure how far away the boundary is.
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Explain how ultrasound is used in medical imaging?
Ultrasound waves can pass through the body, but whenever they reaach a boundary between 2 different media (like fluid in the womb and the skin of the foetus) some of the wave is reflected back and detected. The exact timing and distribution of these
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echoes are processed by a computer to produce a video image of the foetus.
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Explain how ultrasound is used in industrial imaging?
Can be used to find flaws in objects (pipes or materials such as wood or metal) Ultrasound waves entering a material will be reflected by far side of material. If there is a flaw such as a crack inside object, the wave will be reflected sooner.
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What is echo sounding?
It uses high frequency sound waves. It's used by boats and submarines to find out the depth of the water they are in or to locate objects in deep water.
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What can happen when a wave arrives at a boundary between materials?
The wave can be completely reflected or partially reflected. The wave may continue travelling in the same direction but at a different speed, or it may be refracted or absorbed.
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What produces seismic waves?
Earthquakes, which travel out through the Earth. We detect them using seismometers.
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What happens when seismic waves reach a boundary between different layers of material?
Some waves will be absorbed and some will be refracted.
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What happens if waves are refracted?
If the waves are refracted they change speed gradually, resulting in a curved path. However, when the properties change suddenly, the wave speed changes abruptly, and the path has a kink.
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What do the Earth's layers look like?
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What are the 2 types of seismic waves?
P waves and S waves.
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What are P waves?
They are longitudinal. They travel through solids and liquids. They travel faster than S-waves.
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What do P waves look like inside the Earth?
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What are S waves?
S waves are transverse and can't travel through liquids or gases. They're slower than P waves.
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What do S waves look like inside the Earth?
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Card 2

Front

What is the amplitude of a wave?

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The maximum displacement of a point on the wave from its undisturbed position.

Card 3

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What is the wavelength?

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Preview of the front of card 3

Card 4

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What is frequency?

Back

Preview of the front of card 4

Card 5

Front

What is the equation for period?

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Bilal Keyani

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This website is good thoe been wasting alot of time should've known theres ready made flashcards 

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