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Wave Motion
Physics (GCSE) Revision (Waves)
| Statement | Response | Comment |
|---|---|---|
| When sounds bounce back (reflect) from hard surfaces this is called an . . . | ECHO | Sound and light are both waves. |
| When a ray of light is reflected from a shiny surface (e.g. a plane mirror) the angle of incidence is equal to . . . | the angle of reflection. | Angles are measured from the NORMAL. |
| A line drawn at 90 degrees to a surface is called a . . . | NORMAL | Used in measuring angles of reflection and refraction. |
| When rays of light change direction as they cross the boundary between two different substances this is called . . . | REFRACTION | All waves do this. |
| Refraction occurs when light travels between two different materials because . . . | the speed of light is different in each material. | Light slows down in glass and water compared to air. |
| Sound waves are . . . | LONGITUDINAL waves | Compressions and rarefactions travelling through a material ( a push-pull motion on a slinky spring) |
| Light waves are . . . | TRANSVERSE waves | Like a side-to-side motion on a slinky spring. |
| Light waves travel at . . . | the speed of LIGHT | c = 300 000 km/s |
| Sound waves travel much slower than light. Their speed in air is approximately . . . | 330 m/s | Sound travels faster in warm air than in cold. |
| Sound waves can be reflected and . . . | REFRACTED | When they cross the boundary between two different substances. |
| If waves cross a boundary between two different substances at a right angle, there is . . . | NO change of direction. | Only speed and wavelength change. |
| What changes when a light ray crosses a boundary between air and glass, travelling into the glass? | Speed decreases. Wavelength decreases. It bends towards the normal. | These are all part of REFRACTION. |
| If a ray of light travels from glass into air, its speed will . . . | increase. | Light travels faster in air than glass. |
| Waves travelling across the surface of water are . . . | transverse waves. | The surface is displaced at a right angle to the direction of travel of the waves. |
| Water waves can be . . . | refracted and reflected. | Same as any other waves you care to mention. |
| When water waves travel from deep water to shallow water they are refracted because . . . | they travel more slowly in shallow water. | There is more drag from the seabed. |
| When a ray of light travels from glass,Perspex or water into air . . . | some light is refracted and some is reflected from the boundary. | Usually about 50% of the light is reflected. |
| For light travelling from glass to air, if the angle of incidence is greater than a certain angle what happens? | All of the light is reflected inside the glass. | TOTAL INTERNAL REFLECTION. Get the spelling right! |
| What is the name of the largest angle of incidence at which light can just be refracted at a boundary between glass and air? | Critical angle | About 42 degrees for glass / air. |
| Light can travel along an optic fibre because of . . . | total internal reflection. | No refraction involved. |
| Optic fibres can be used to send telephone messages in the form of . . . | pulses of light. | Infra red lasers are used for this. |
| Sound waves travel through solids, liquids and gases as . . . | longitudinal waves. | Push a slinky spring away from you and back again. |
| When a wave moves through a gap, or past an obstacle, it . . . | spreads out from the edges. | This is called diffraction. |
| Diffraction of radio waves can improve radio reception in hilly areas because . . . | the waves bend over the summit and down into the valleys. | This doesn't work with TV or microwaves because they have a shorter wavelength. |
| Diffraction occurs more strongly when . . . | the wavelength is similar to the size of the obstacle. | A hill of height 1000m will diffract radio waves of the same wavelength. |
| When white light passes through a 60 degree prism . . . | a spectrum of colours is produced. | Isaac Newton explained this by saying that white is a mixture of all the other colours. |
| Different colours of light have different . . . | wavelengths. | Red has the longest, violet the shortest. |
| When a spectrum is produced by a prism the effect is called . . . | dispersion. | Different colours travel at different speeds in glass - red slows down least. |
| Which colour is refracted most by a prism? | Violet | Violet Veers Violently |
| There are many more kinds of radiation than we can see with our eyes. The full range is called the . . . | electromagnetic spectrum | It extends to very large and very small wavelengths. |
| The type of electromagnetic radiation which has the longest wavelength is . . . | radio waves. | Typically over 1 kilometre in length. |
| The type of electromagnetic radiation which has the shortest wavelenth is . . . | gamma rays. | Wavelength is less than the size of an atom. |
| When radiation is absorbed, the energy it carries makes . . . | the substance which absorbs it hotter. | Lying in the Sun makes me hot! |
| Electromagnetic radiation may also . . . | create an alternating current with the same frequency as the radiation. | That's how a radio or TV works. |
| Radio waves are used to . . . | transmit radio and TV programmes between different points on Earth's surface. | Range is limited by line of sight. |
| Longer wavelength radio signals can be reflected from an electrically charged layer in Earth's upper atmosphere called . . . | the ionosphere. | This enables signals to be sent between distant points despite the curvature of Earth's surface |
| Microwave radiation of short wavelength which can pass through Earth's atmosphere is used to . . . | send information to and from satellites and within mobile phone networks. | To receive information from a satellite you will need a satellite DISH. |
| A microwave oven can be used for cooking because . . . | water molecules in food strongly absorb microwaves of the correct wavelength. | No metal objects and certainly not your hands! |
| Toasters, grills and radiant heaters make use of . . . | infra red radiation. | This is emitted from warm bodies such as animals and plants. |
| A TV remote control uses . . . | infra red radiation. | You might not see it yourself but try using a video camera ! |
| Light can be sent down optical fibres to allow doctors to see inside a patient's body. The device is called an . . . | endoscope. | It can be used at both 'ends' - but only by a qualified medical person please ! |
| Sunbeds make use of . . . | ultraviolet radiation | Careless exposure can result in skin cancer (melanoma) so use Factor 25 at least ! |
| Special coatings which absorb UV and emit visible light are used in . . . | fluorescent lamps and security coding. | Check out your white shirt at the discotheque ( yeah, I know that dates me!) |
| X-rays are used to produce shadow pictures of bones because . . . | X-rays do not easily pass through bone or metal. | It can be used at airports for screening your luggage - so leave those scissors at home. |
| Gamma radiation is used to . . . | kill harmful bacteria in food, sterilise surgical instruments and kill cancer cells. | Those party forks you use at barbecues have been inside a nuclear reactor you know. |
| Microwaves are absorbed by the water in cells which may be . . . | damaged or killed by the heat released. | So keep your hands out of the microwave and keep your mobile phone at a safe distance too. |
| Infra red is absorbed by the skin and felt as . . . | heat. | Nice. |
| Ultraviolet can pass through the skin to deeper tissues. The darker the skin . . . | the more UV it absorbs and the less reaches deeper tissues. | See, there's a reason for everything. |
| X-rays and gamma rays mostly pass through soft tissues but some . . . | is absorbed by the cells. | No exposure is good exposure. |
| High doses of UV, X and gamma radiation can kill normal cells. Lower doses can . . . | cause normal cells to become cancerous. | Very high doses are needed to kill cancer cells, but healthy cells are also killed. It is a high risk strategy. |
| Information such as speech or music can be converted into . . . | electrical signals that can be sent long distances through cables or using electromagnetic waves as carriers. | Traditional methods: copper wires and radio signals. |
| Information can be converted into light or infra red signals and sent . . . | along optic fibres. | Modern methods: cheaper, less loss of energy so more efficient. |
| Signals which vary continuously in amplitude and/or frequency are called . . . | analogue signals | Old fashioned vinyl records and terrestrial TV ( not digital) |
| Signals can be coded as a series of pulses which have two states, on or off. These are called . . . | digital signals | Now we're talking ! |
| One advantage of difgital signals over older analogue signals is . . . | higher quality - the signals do not change their information during the transmission process. | Analogue signals are prone to distortion. On is on and off is still off. |
| A major advantage of digital signals is . . . | their information carrying capacity. | More information can be transmitted in a given time than with analogue signals. |
| As signals travel they become weaker. Random additions to the signal are called . . . | NOISE | Noise adds to both types of signal. |
| With analogue signals, different frequencies may weaken to different extents. When amplified . . . | the signal becomes less like the original. Its quality deteriorates. | Noise is also amplified along with any differences. |
| Even though digital pulses weaken with distance, the quality is maintained because . . . | noise is of low amplitude and below the level recognised as 'on'. It is treated as 'off'. | The voltage needed for an 'on' state is much higher than the noise level. |
| Sounds are produced when object vibrate. The greater the amplitude of vibrations . . . | the louder the sound. | Turn it up ! |
| The number of complete vibrations each second is called the . . . | frequency ( measured in hertz, Hz) | The higher the frequency of a sound the higher its PITCH |
| Electronic systems can produce waves which have a frequency higher than humans can hear called . . . | ultrasound or ultrasonic waves | Above 20kHz, I give up. |
| Ultrasonic waves are used in medicine for . . . | pre-natal scanning | Doesn't harm the foetus like X-rays would. |
| In industry, ultrasound is used for . . . | cleaning delicate mechanisms and for quality control | Can detect cracks in welds, moulded castings etc. |
| The information needed for an ultrasound scan to be useful is . . . | the time taken for an echo to return to the detector. | The distance to the reflecting boundary can be calculated if the speed of sound in the material is known. |
| Our knowledge of the structure of the Earth comes from studying how the shock waves from earthquakes travel through it. These are called . . . | seismic waves. | Earthquake intensity is measured on the Richter scale. |
| Earthquakes produce waves which can be detected using . . . | seismographs or seismometers. | They produce a pen and ink trace on a rotating drum of paper. |
| The outermost layer of the Earth is very thin and is called the . . . | crust. | If the Earth was the size of an apple, the crust would only be the thickness of the skin. |
| The Earth's core extends about halfway to the surface. It consists of an inner and an outer core. The outer core is . . . | liquid nickel and iron. | The inner core is a solid ball of metal. |
| The layer of rock surrounding the core extends almost to the surface and is called the . . . | mantle | It has the properties of a solid but it can flow very slowly. |
| The overall density of the Earth is much greater than the mean densities of the rocks that form the crust. This suggests that . . . | the interior of the Earth is much denser. | Density increases with depth due to the increasing pressure of the overlying rocks. |
| What are the two types of seismic waves that travel through the interior of the Earth? | P and S waves. | There are surface waves as well which only travel through the crust. |
| Which type of seismic waves are faster? | Primary (P) waves | They are recorded first by seismographs at the start of an earthquake. |
| What is the difference between the two types of seismic waves? | P waves are longitudinal, S waves are transverse. | P waves are compression waves. S waves are shear waves. |
| Which type of seismic wave cannot travel in a liquid? | S waves | They need a rigid (solid) medium. |
| Seismic waves travel in curved paths through the interior of the Earth because . . . | they are being refracted. | They travel faster as they go deeper. |
| The speed of seismic waves increases with depth because . . . | the density of rock increases with depth. | Seismic waves travel faster in denser material. |
| The speed and direction of P waves change abruptly as they reach the outer core because . . . | its density suddenly decreases. | Liquids are less dense than solids. |
| We know that the outer core is a liquid because . . . | S waves can't travel through it. | Only P waves can pass right through the Earth's core. |
| Some seismometers cannot detect the S waves from an earthquake. Why is this ? | S waves can't pass through the core. | If the seismometer is in a 'shadow zone', only P waves can reach it. |
| The fact that the edges of land masses which are separated by thousands of kilometres of ocean have shapes which fit quite closely suggests that . . . | they may have been part of larger land mass which spli apart. | e.g. south east America and west Africa |
| Wegener's theory of continental drift is supported by . . . | similar patterns of rocks and fossils on different continents | Or perhaps a land bridge which broke apart could explain this |
| The upper part of Earth's mantle and crust is called the . . . | lithosphere | It is moving on top of denser material below |
| The pieces of Earth's lithosphere which are moving are called . . . | tectonic plates | Like rafts of polystyrene floating on denser water |
| The Earth's tectonic plates are moving slowly at a speed of about . . . | a few centimetres a year | We can measure this by timing radio signals |
| The process which drives plate tectonics is . . . | convection currents in the mantle | The energy is provided by radioactive decay which releases heat |
| At the boundaries between tectonic plates we find . . . | more earthquakes and volcanic eruptions | You can see a map of this in your text book |
| Where two plates meet they may slide past each other. This is known as a . . . | transform fault | They rub and produce friction e.g. California |
| When two tectonic plates approach each other, one of them may be driven down. This is called . . . | subduction | Old crust is melted to form volcanoes |
| Sea floor spreading is caused when . . . | two tectonic plates move apart | New magama rises to fill the gap |
| Evidence for sea-floor spreading is provided by . . . | magnetic reversal patterns in oceanic crust | This confirms the theory of plate tectonic and also shows the Earth's magnetic field can flip over. |
Created by:
J Thomson
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