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tempArray[arrayIndex++] = "p03lfp02a | Waves carry energy from one place to another."
tempArray[arrayIndex++] = "p03lfp02b | For example, energy from the Sun reaches us via waves travelling across the vacuum of space."
tempArray[arrayIndex++] = "p03lfp02c | Sound, light and radio signals all travel in the form of waves."
tempArray[arrayIndex++] = "p03lfp02d | There are two types of wave, Transverse and Longitudinal."

tempArray[arrayIndex++] = "p03lfp03a | If you hold a piece of rope, and quickly move your arm up and down, you will see wave motion."
tempArray[arrayIndex++] = "p03lfp03b | Each bit of the rope vibrates at right angles to the direction that the waves are travelling."
tempArray[arrayIndex++] = "p03lfp03c | Waves on ropes, waves on the surface of water, and electromagnetic waves, like light, are all transverse waves."

tempArray[arrayIndex++] = "p03lfp04a | In a longitudinal wave the vibrations move in the same direction as the wave is travelling."
tempArray[arrayIndex++] = "p03lfp04b | The ‘squashes’ are called compressions. The air pressure here is higher than normal."
tempArray[arrayIndex++] = "p03lfp04c | The ‘stretches’ are called rarefactions; the air pressure here is lower than normal."
tempArray[arrayIndex++] = "p03lfp04d | Sound waves and compression waves in springs are examples of longitudinal waves."

tempArray[arrayIndex++] = "p03lfp05a | Sounds can be produced in many ways. Every sound is produced by vibrations."
tempArray[arrayIndex++] = "p03lfp05b | One way of looking at a sound wave is to change the vibrations of the air into an electrical signal using a microphone."
tempArray[arrayIndex++] = "p03lfp05c | If the microphone is connected to an oscilloscope, the pattern of the sound wave appears on the screen as a trace."
tempArray[arrayIndex++] = "p03lfp05d | Sound waves can travel through gases, like air."
tempArray[arrayIndex++] = "p03lfp05e | Sound waves can travel through solids such as the wall of the room."
tempArray[arrayIndex++] = "p03lfp05f | Sound waves can travel through liquids, like water."
tempArray[arrayIndex++] = "p03lfp05g | Sound waves cannot travel through a vacuum, like space, because there are no particles to vibrate and carry the sound wave."

tempArray[arrayIndex++] = "p03lfp06PQ | "

tempArray[arrayIndex++] = "p03lfp07a | The distance between two successive peaks or between any place on one wave and the same place on the next wave is the wavelength."
tempArray[arrayIndex++] = "p03lfp07b | The number of complete waves or oscillations in one second is the frequency (f). It is measured in hertz (Hz)."
tempArray[arrayIndex++] = "p03lfp07c | So a frequency of 3Hz means that 3 waves have passed in one second."
tempArray[arrayIndex++] = "p03lfp07d | A high-pitched note has a high frequency."
tempArray[arrayIndex++] = "p03lfp07e | A low-pitched note has a low frequency."
tempArray[arrayIndex++] = "p03lfp07f | Humans can hear a sound between the frequencies 20Hz to 20000Hz. Sound with a very high frequency that is too high for humans to hear is called ultrasound."
tempArray[arrayIndex++] = "p03lfp07g | The height or displacement is called the amplitude."
tempArray[arrayIndex++] = "p03lfp07h | A loud sound will have a large amplitude."
tempArray[arrayIndex++] = "p03lfp07i | A soft sound will have a small amplitude."
tempArray[arrayIndex++] = "p03lfp07j | The wave equation applies to both longitudinal waves like sound and transverse waves like light."

tempArray[arrayIndex++] = "p03lfp08PQ | "

tempArray[arrayIndex++] = "p03lfp09a | We can see things, like the sun, because they give off their own light."
tempArray[arrayIndex++] = "p03lfp09b | We see other things because light bounces off them."
tempArray[arrayIndex++] = "p03lfp09c | They reflect light into our eyes."
tempArray[arrayIndex++] = "p03lfp09d | By arranging a mirror at just the right angle, we can see things which otherwise would be outside our field of view."
tempArray[arrayIndex++] = "p03lfp09e | When a ray of light is reflected from a mirror, or any flat, shiny surface, the angle at which it leaves the surface is the same as the angle at which it meets the surface. This is called the law of reflection."
tempArray[arrayIndex++] = "p03lfp09f | The reflected light has changed direction."

tempArray[arrayIndex++] = "p03lfp10a | Sound waves can also be reflected. The reflected sound is called an echo."
tempArray[arrayIndex++] = "p03lfp10b | Distances can be measured using echoes."
tempArray[arrayIndex++] = "p03lfp10c | For example, ships use echo sounders to measure the depth of water beneath them."
tempArray[arrayIndex++] = "p03lfp10d | An echo sounder sends a burst of sound waves towards the seabed. Then it measures the time taken for the echoes to return."
tempArray[arrayIndex++] = "p03lfp10e | The longer it takes for the echo to return, the deeper the water."
tempArray[arrayIndex++] = "p03lfp10f | We can calculate the distance using distance travelled = speed  x  time."
tempArray[arrayIndex++] = "p03lfp10g | A burst of sound takes 0.2 seconds to reach the seabed and then return, and the speed of sound in water is 1400m/s."
tempArray[arrayIndex++] = "p03lfp10h | The depth of water is 280 metres divided by 2, because the sound has to travel down to the seabed and back."

tempArray[arrayIndex++] = "p03lfp11PQ | "

tempArray[arrayIndex++] = "p03lfp12a | There are situations when we need to change the direction of light, but cannot use mirrors."
tempArray[arrayIndex++] = "p03lfp12b | For example, the lenses in spectacles must allow light to pass through them, but must also change the direction of the light by the right amount to correct any defects in the vision of the wearer, so that the person will then be able to see objects clearly."
tempArray[arrayIndex++] = "p03lfp12c | As the light crosses the boundary between air and glass, the pathway of the light is bent; we say it has been refracted."
tempArray[arrayIndex++] = "p03lfp12d | Light can travel through many different transparent media."
tempArray[arrayIndex++] = "p03lfp12e | These include air, water, a vacuum (like space), glass, diamonds, plastic."

tempArray[arrayIndex++] = "p03lfp13a | Whenever light passes from one medium to another, refraction happens."
tempArray[arrayIndex++] = "p03lfp13b | The light is refracted because it travels more slowly through the glass. It is refracted again as it leaves the glass, because of the change in speed."
tempArray[arrayIndex++] = "p03lfp13c | Some light is also reflected as the light passes into the block."

tempArray[arrayIndex++] = "p03lfp14a | Water never looks as deep as it really is, because of refraction."
tempArray[arrayIndex++] = "p03lfp14b | Light reflected from a fish in the water travels towards a bird overhead."
tempArray[arrayIndex++] = "p03lfp14c | As the light passes from the water into the air, it refracts away from the normal because it has travelled from water, which is a denser substance, into air, which is a less dense substance."
tempArray[arrayIndex++] = "p03lfp14d | From above, the rays seem to come from a point, which is not so deep. So the fish seems closer."
tempArray[arrayIndex++] = "p03lfp14e | The bird allows for refraction. If the bird dives to where the fish seems to be, it will miss."

tempArray[arrayIndex++] = "p03lfp15a | Sound waves are also refracted."
tempArray[arrayIndex++] = "p03lfp15b | Whales use refraction to focus sound waves inside their heads."
tempArray[arrayIndex++] = "p03lfp15c | In a whale’s head the layers of different tissue bend the sound waves as they pass from layer to layer."
tempArray[arrayIndex++] = "p03lfp15d | The waves change speed as they pass from layer to layer."

tempArray[arrayIndex++] = "p03lfp16a | When light crosses from one medium to another some of it is reflected."
tempArray[arrayIndex++] = "p03lfp16b | Most of the light is refracted and emerges into the air."
tempArray[arrayIndex++] = "p03lfp16c | As the angle of incidence increases, the amount of light reflected increases."
tempArray[arrayIndex++] = "p03lfp16d | When the angle of incidence is above a critical angle, the light does not emerge, it is totally internally reflected."

tempArray[arrayIndex++] = "p03lfp17a | Total internal reflection is used to pass light through thin fibres of glass, called optical fibres."
tempArray[arrayIndex++] = "p03lfp17b | The light hits the side of the fibre at an angle bigger than the critical angle. All the light is reflected."
tempArray[arrayIndex++] = "p03lfp17c | The light is reflected many times, and it emerges from the other end of the fibre almost as bright as it went in. Very little energy has been lost."

tempArray[arrayIndex++] = "p03lfp18a | Waves can also be drawn using lines called wavefronts."
tempArray[arrayIndex++] = "p03lfp18b | For transverse waves, each wavefront is the top of a wave."
tempArray[arrayIndex++] = "p03lfp18c | For a longitudinal wave, like a sound wave, the wavefronts indicate the area of compression or high pressure."

tempArray[arrayIndex++] = "p03lfp19a | To explain why light and sound are described as waves, we can compare the behaviour of water waves."
tempArray[arrayIndex++] = "p03lfp19b | The waves are reflected by the barrier."
tempArray[arrayIndex++] = "p03lfp19c | The angle of reflection is the same as the angle of incidence at which the waves approached the barrier."
tempArray[arrayIndex++] = "p03lfp19d | The frequency, speed and wavelength remain unchanged."

tempArray[arrayIndex++] = "p03lfp20PQ | "

tempArray[arrayIndex++] = "p03lfp21a | Waves travel quickly across deep water."
tempArray[arrayIndex++] = "p03lfp21b | When the water gets shallower near the beach, the waves slow down."
tempArray[arrayIndex++] = "p03lfp21c | The part of the wave that meets the shallow water slows down first."
tempArray[arrayIndex++] = "p03lfp21d | The part of the wave that is still over deep water continues at the same speed, so the wave changes direction."
tempArray[arrayIndex++] = "p03lfp21e | As the waves slow down they also get closer together. The frequency of the waves stays the same, but the speed and wavelength change."
tempArray[arrayIndex++] = "p03lfp21f | Sound and light waves are refracted because they travel faster through some substances than others. For example, light travels slower through glass or plastic than it does through air."
tempArray[arrayIndex++] = "p03lfp21g | Scientists say that because sound and light waves are refracted and reflected much like water waves, this provides evidence for thinking that light and sound travel in the form of waves."

tempArray[arrayIndex++] = "p03lfp22a | Reflection and refraction are examples of wave behaviour. There is a third example called diffraction."
tempArray[arrayIndex++] = "p03lfp22b | When water waves go past an obstacle they spread out into the space behind the object."
tempArray[arrayIndex++] = "p03lfp22c | This spreading out is called diffraction."
tempArray[arrayIndex++] = "p03lfp22d | The effect is more noticeable when the size of the gap is similar to the wavelength of the waves."
tempArray[arrayIndex++] = "p03lfp22e | As a result of diffraction the energy carried by the waves becomes spread out."

tempArray[arrayIndex++] = "p03lfp23a | Sound waves have wavelengths from a few centimetres to a few metres."
tempArray[arrayIndex++] = "p03lfp23b | These long wavelengths can be diffracted around the edges of buildings and doorways. This is one of the reasons why you can hear sounds around corners."
tempArray[arrayIndex++] = "p03lfp23c | Long and medium radio waves will diffract around hills. Your radio will pick them up, even down in a valley."
tempArray[arrayIndex++] = "p03lfp23d | Light can also be diffracted, but because the wavelength is very small the effects are not noticed unless the gaps through which the light passes are also very small."

tempArray[arrayIndex++] = "p03lfp24a | When earthquakes happen, rocks suddenly move and crack deep in the Earth."
tempArray[arrayIndex++] = "p03lfp24b | The place where this happens is called the epicentre."
tempArray[arrayIndex++] = "p03lfp24c | The rocks shudder, and vibrations spread outwards from the epicentre."
tempArray[arrayIndex++] = "p03lfp24d | The spreading vibrations are called seismic waves."
tempArray[arrayIndex++] = "p03lfp24e | Some seismic waves are transverse, and some are longitudinal."
tempArray[arrayIndex++] = "p03lfp24f | Waves from the earthquake spread out and reach seismic research stations around the world."
tempArray[arrayIndex++] = "p03lfp24g | At these research stations, sensitive instruments can pick up small vibrations. The instruments make records of the vibrations, called seismograms."
tempArray[arrayIndex++] = "p03lfp24h | Our knowledge of the structure of the Earth comes mainly from studying how shockwaves or seismic waves from earthquakes travel through it."

tempArray[arrayIndex++] = "p03lhp25a | Earthquakes produce surface waves that can cause earthquake damage."
tempArray[arrayIndex++] = "p03lhp25b | Earthquakes also produce two other types of wave (P waves and S waves) that can travel through the Earth."
tempArray[arrayIndex++] = "p03lhp25c | The three types of wave have three different speeds, because they travel through or across the Earth in different ways."
tempArray[arrayIndex++] = "p03lhp25d | The faster travelling P waves - primary waves - are longitudinal and travel through liquids as well as solids."
tempArray[arrayIndex++] = "p03lhp25e | They are able to travel through the interior of the Earth."
tempArray[arrayIndex++] = "p03lhp25f | S waves - secondary waves - are slower travelling, transverse waves and travel only through solids."

tempArray[arrayIndex++] = "p03lfp26a | The velocities of the P waves and S waves change as the waves pass through different layers."
tempArray[arrayIndex++] = "p03lfp26b | The changing velocities curve the paths of the waves."
tempArray[arrayIndex++] = "p03lfp26c | This is refraction due to change in speed."

tempArray[arrayIndex++] = "p03lfp27a | The refraction is only gradual. When the state of the transmitting medium changes suddenly, e.g. when moving from solid to liquid, the wave direction also changes suddenly."
tempArray[arrayIndex++] = "p03lfp27b | This refraction is due to a change in density of the different layers."
tempArray[arrayIndex++] = "p03lfp27c | The waves travel more slowly through dense solids than through liquids."
tempArray[arrayIndex++] = "p03lfp27d | This is refraction due to change in speed."

tempArray[arrayIndex++] = "p03lfp28a | Scientists explain their observations of these seismic waves as follows:"
tempArray[arrayIndex++] = "p03lfp28b | In the Earth, density increases with depth. This changes the speed of seismic waves so that they are refracted - or bent - and follow a curved path."
tempArray[arrayIndex++] = "p03lfp28c | The Earth has a central core. The outer part must be molten because S-waves are blocked and S-waves cannot travel through liquids."
tempArray[arrayIndex++] = "p03lfp28d | The pattern of P-wave refraction suggests that the core is very dense, and is probably mainly iron."

tempArray[arrayIndex++] = "p03lfp29 | "

arrayIndex = 1;
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