Audio Transcrip

Contents

Unit 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Unit 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Unit 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Unit 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Unit 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Unit 6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Unit 7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Unit 8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Unit 9 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Unit 10 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Unit 11 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Unit 12 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

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2 K ESSENTIAL NATURAL SCIENCE 2 K PHOTOCOPIABLE MATERIAL © 2008 Richmond Publishing / Santillana Educación, S.L. K

Track 1

Unit 1. Page 14

Which type of cell nutrition?

Study the diagrams and text on cell nutrition. Listenand say: autotrophic nutrition, heterotrophic nutrition,or both.

• This type of nutrition is characteristic of cellswhich feed on organic matter produced by otherliving beings.

• This type of nutrition is characteristic of cellswhich make their own organic matter frominorganic matter.

• This type of nutrition takes place in plants.

• This type of nutrition takes place in animals,fungi and many bacteria.

• In this type of nutrition, cells use oxygen toproduce energy, carbon dioxide and water.

• In this type of nutrition, as a result of catabolism,carbon dioxide is produced and releasedoutside.

• In this type of nutrition, using energy fromcatabolism and simple molecules, complexorganic molecules are produced.

Track 2

Unit 1. What should you know?

The basis of lifeVital functions.

• The nutrition function is the process in whichliving beings obtain the matter and the energynecessary for life.

• The interaction function is the process in whichliving beings relate with their surroundingenvironment.

• The reproduction function is the process by which new, individual living beings areproduced.

Organic and inorganic biomolecules.

Biomolecules are the building blocks of life.

Organic biomolecules.

They include: carbohydrates, lipids, proteins, andnucleic acids.

Inorganic biomolecules.

These are water, and mineral salts.

Cells.

• Cells are the structural and functional units of allliving organisms.

• They have three basic structures: the cellmembrane, the cytoplasm, and the nucleus withgenetic material.

• According to their genetic material, cells can beprokaryotic or eukaryotic.

• There are plant and animal cells.

Cellular nutrition.

Cellular metabolism includes two types of metabolicreactions: catabolism and anabolism.

Depending on the type of nutrients, cellular nutritioncan be:

• Autotrophic. This is characteristic of cells whichmake their own organic matter from inorganicmatter, using an energy source, mainly sunlight.

• Heterotrophic. This is characteristic of cellswhich feed on organic matter produced by otherliving beings.

Cellular respiration.

Cellular respiration describes the metabolic reactionsto obtain energy from specific organic molecules.

Cellular division.

Cellular division is the process by which a cell dividesinto two cells, called daughter cells.

Track 3

Unit 2. 3

Which type of nutrition?

Study the drawing of the zebra.

Listen and identify the parts of the digestive system invertebrates. Say: small intestine, large intestine, anus,oesophagus, mouth, or stomach.

• This is where food is moved from the mouth to the stomach.

• This is where absorption of nutrients anddigestion takes place.

• This is where egestion takes place.

• This is where gastric digestion takes place.

• This is where food is chewed and mixed with saliva.

• This is where undigested food is transformed into faeces.

UNIT 2

UNIT 1

Audio transcript

3K ESSENTIAL NATURAL SCIENCE 2 K PHOTOCOPIABLE MATERIAL © 2008 Richmond Publishing / Santillana Educación, S.L. K

Track 4


NutritionDigestion.

Digestion takes place in the digestive system.

There are four stages:

• Ingestion, which is the intake of food into thebody.

• Digestion, which is the transformation of foodinto nutrients.

• Absorption, which is the passage of nutrients into the blood.

• Egestion, which is the elimination of undigestedand waste products.

Respiration.

Respiration takes place in the respiratory system.

There are four types of respiration:

• Cutaneous, when gas exchange occurs throughthe skin.

• Branchial, when gas exchange occurs throughthe gills.

• Tracheal, when gas exchange occurs throughthe tracheae.

• Pulmonary, when gas exchange occurs in thelungs.

Circulation.

Circulation is carried out by the circulatory system.

There are several types of circulatory systems. They are:

• Open. In this system, the circulating fluid flowsthrough the body cavity, and bathes the internalorgans directly.

• Closed. In this system, the blood alwayscirculates inside blood vessels.

There are two types of closed circulatory system:

• In a simple circulatory system, the blood onlypasses through the heart once.

• In a double circulatory system, thee bloodpasses through the heart twice.

Excretion.

Excretion involves the collection and expulsion ofwaste products produced by cellular activity.

Excretion is carried out by the Malpighian tubules ininsects, and the excretory system in vertebrates.

Plant nutrition.

Plant nutrition consists of the following processes:

• Absorption. This is the movement of water andmineral salts, that is, raw sap, from the ground to the interior of the roots.

• Transport of the raw sap. The raw sap goes fromthe roots to the green parts of the plant, throughthe xylem vessels.

• Exchange of gases. This occurs in the leaves by means of the stomata.

• Photosynthesis. This occurs in the chloroplastsof the green parts of the plant.

• Transport of elaborated sap. The elaborated sapgoes from the green parts of the plants throughthe phloem vessels.

Track 5

Unit 3. 4

Which sense organ?

Look at the table, listen and identify the sense organs.

• This organ detects light.

• This organ detects chemical substancesdissolved in air or water.

• This organ detects pressure, pain andtemperature.

• This organ is covered in tiny taste buds.

• This organ detects chemical substancesdissolved in water.

• This organ can distinguish a wide range ofsounds.

Track 6


Interaction and coordination

Animal coordination and interaction.

Stimuli.

Stimuli are all the information which a living beingreceives. They provoke a response. Stimuli arereceived through interaction.

Receptors.

Receptors are structures which detect external and internal stimuli.

• In animals, they are found in the sense organs.

• In plants, they are found in the cells.

The nervous system.

The nervous system regulates and coordinates the body’s activities and functions. It consists of the central nervous system, made up of the brainand the spinal cord, and the peripheral nervoussystem made up of the nerves.

UNIT 3


• The nervous system produces responses whichare sent to the responsive organs, calledeffectors.

• Nerves carry nervous impulses from the nervecentres to all other parts of the body.

• Less-developed animals have a simpler nervoussystem.

Effectors.

Effectors are organs which produce a response. Thereare two types of response to stimuli:

• Motor. The response is movement. It is carriedout by the motor system.

• Endocrine. The response is the release ofhormones. It is carried out by glands.

Plant coordination and interaction.

There are two types of response to external stimuli:

Tropism.

This refers to permanent responses which producechanges in the direction of the plant’s growth. Thereare several types of tropism:

• Geotropism. The response is provoked by gravity.

• Phototropism. The response is provoked by light.

• Hydrotropism. The response is provoked by water.

• Thigmotropism. The response is provoked bycontact.

Nastic movements.

Nastic movements are temporary responses of particular parts of the plant.

Track 7

Unit 4. 7

Which type of fertilisation?

Look at the diagrams of external and internalfertilisation. Then listen and say true or false.

• External fertilisation takes place in deer.

• Internal fertilisation is the fusion of the male andfemale gametes inside the female body.

• Both internal and external fertilisation require theunion of a spermatozoon and an ovum.

• In internal fertilisation, the female releases manyunfertilised eggs.

• When the nuclei of an ovum and a spermatozoonunite, they form a zygote.

• Internal fertilisation involves a male copulatingorgan.

Track 8


ReproductionReproduction in animals.

Asexual reproduction.

There are two main types of asexual reproduction inanimals:

• Fragmentation, which is the division of theprogenitor’s body in various fragments, creatingnew individuals.

• Gemmation, which is when small buds appearon the body of the progenitor. These buds canseparate from the parent, or can remain joined,and form a colony.

Sexual reproduction.

Sexual reproduction requires two members of theopposite sex, a male and a female. They have differentreproductive organs, called gonads.

• The male gonads are the testicles, wherespermatozoa are produced.

• The female gonads are the ovaries, where ovaare produced.

Fertilisation is the union of an ovum and aspermatozoid, or spermatozoon to form a zygote.During the embryonic development, the zygotedevelops until it becomes a completely formed animal.

Reproduction in plants.

Asexual reproduction.

There are two main types of asexual reproduction inplants:

• Vegetative reproduction, occurs when plantscreate new individuals from a particular organ,mainly the stem. This occurs through stolons,bulbs, stem tubers, and rhizomes.

• Spores formation, which is when a cell from anindividual divides repeatedly, and variousdaughter cells, called spores, are formed. Theseindividual cells alone create new plants.

Sexual reproduction.

Sexual reproduction in plants with seeds has variousstages:

• Pollination. Pollen is transported from thestamens to the pistil.

• Fertilisation. The male and the female gametesfuse to form the zygote inside the ovary. Thezygote grows into an embryo. The ripened ovulebecomes the seed which contains the embryo.

• The formation of the fruit. The fruit originatesfrom the ripened ovary. Its function is to disperseand protect the seed.

UNIT 4


Track 1

Unit 5. Page 62

Can you identify the biotic relations?

Look at the texts on biotic relations. Listen and identifythe type of relation:

• This is a relationship in which one species, a parasite, lives at the expense of anotherspecies, the host.

• This is a relationship between two or morespecies for mutual benefit.

• This is a relationship in which related individualslive together.

• This is the relationship in which an individual,the predator, kills and eats another living being,the prey.

• Groups of individuals which live together forsome time, for example, migrating birds, havethis type of relationship.

• This relationship is when groups of individualsare organised in a hierarchy.

• This relationship is between two living beingswhere one benefits, but the other is not affected.

• This relationship is one in which relatedindividuals live together to procreate and protecttheir young.

• This is a form of commensalism where oneorganism uses another organism for housing.

Track 10


The structure of ecosystems The components of an ecosystem.

An ecosystem includes the biocenosis, the biotope,and the biotic and abiotic relationships establishedbetween them.

The biocenosis is all the living beings which inhabit a natural area, and the relationship between them.

The biotope is the physical environment of theecosystem and its characteristics.

Habitat or ecological niche.

• The habitat is the physical environment whereindividuals of a particular species live, and areadapted.

• The ecological niche is the function which aparticular species has within an ecosystem.

Trophic levels in an ecosystem.

A trophic level includes all of the organisms whichobtain the matter and energy they need in the sameway. The trophic levels are:

• Producers. These are autotrophic organisms thatmake their own organic matter from inorganicmatter.

• Consumers. These are heterotrophic organismswhich feed off organic material which hasalready been produced.

There are three types of consumers:

• Primary consumers, called herbivores.

• Secondary consumers. These are carnivores andsome omnivores.

• Tertiary consumers. These are some carnivoresand some omnivores.

• Decomposers. These are heterotrophicorganisms which transform organic matter backinto inorganic matter.

In ecosystems, energy has a unidirectional flow. Matterhas a cyclical flow.

Trophic dynamics.

Food chains, or food webs, are used to represent therelationships among organisms in an ecosystem.

The trophic structure of an ecosystem can also berepresented graphically by trophic pyramids. There arethree types: number pyramids, biomass pyramids andenergy pyramids.

Relationships among organisms can be intraspecific or interspecific.

• Intraspecific relationships are interactions amongindividuals of the same species.

• Interspecific relationships are relationshipsamong individuals of different species.

Track 11

Unit 6. Page 71

Which zone in a marine ecosystem?

Look at the diagram of a marine ecosystem. Listen andchoose the correct answer.

• This is the part of the open sea which is a longway from the coast.

Is this the pelagic zone or the neritic zone?

• This is the area between tide marks.

Is this the intertidal zone or the abyssal plain?

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UNIT 5


• This is the deepest part of a marine ecosystem.

Is this the intertidal zone or the abyssal plain?

• The sea floor is covered with seaweed and is veryrich in life.

Is this the pelagic zone or the neritic zone?

• This area is affected by the movement of the waves.

It is submerged at high tide and exposed at lowtide. Is this the neritic zone or the intertidal zone?

• There are not many sources of food, and verylittle light reaches here.

Is this the pelagic zone or the abyssal plain?

Track 12


EcosystemsTerrestrial ecosystems.

The factors that most influence the distribution of livingbeings are: temperature, light, and humidity.

According to the climatic zone, the major terrestrialecosystems are:

• The Frigid Zone. This includes: the Tundra,which has a very cold climate and scantprecipitation; and the Taiga, which has abundantprecipitation in the form of snow.

• The Temperate Zone. This includes: deciduousforest, which has abundant rainfall throughoutthe year; and Mediterranean forest, which hasirregular rainfall.

• The Torrid Zone. This includes: grassland, whichhas constant high temperatures; desert, whichhas a very dry climate; and rainforest, which hasabundant rainfall and high temperatures.

Aquatic ecosystems.

The factors that most influence the distribution of livingbeings are: light; temperature; pressure; salinity; andoxygen.

The main aquatic ecosystems are:

• Marine ecosystems.

• Freshwater ecosystems. These are divided into:lentic ecosystems, which consist of standing orstill water, such as pools, ponds and lakes; andlotic ecosystems, which consist of running water,such as streams and rivers.

Track 13

Unit 7. Page 80.

How much do you know about meteorology?Listen to these definitions about aspects ofmeteorology, then say if they are true or false.

• Meteorology is the science which studies theatmosphere and its phenomena, includingweather and climate.

True or false?

• Isobars are lines which connect points of equalrainfall.

True or false?

• Pressure is measured in isobars.

True or false?

• Snow is a type of precipitation which consists of irregular balls of ice.

True or false?

• Low pressure areas are called anticyclones.

True or false?

• Clouds originate in low pressure areas, onmountain slopes, or near the ground.

True or false?

• Winds form because air tends to move from highpressure areas to low pressure areas.

True or false?

• Air rises in a low pressure area, cools, and formsclouds.

True or false?

Track 14


Energy from the Sun

Effects.

Energy from the Sun affects the activity in theatmosphere and hydrosphere, and many otherprocesses on the surface of the Earth.

Energy from the Sun combined with gravity, isresponsible for the geological agents that shape the Earth.

The Earth warms unequally as a result of its sphericalshape and the filtering effect of the atmosphere.

The unequal warming of the Earth creates atmosphericand oceanic currents.

Atmospheric phenomena.

Local atmospheric phenomena occur within a fewkilometres of the surface of the Earth.

UNIT 7


These phenomena include: the formation of thermals,storms, sea breezes, land breezes, valley breezes, andthermal inversion.

Meteorology is the science which deals with theatmosphere and its phenomena, including weather,and climate.

Global atmospheric phenomena include the formationof low pressure areas, called depressions, highpressure areas, called anticyclones, winds, clouds,and precipitation.

Uses of solar energy.

Solar energy can be used to produce heat with solarwater heaters, and to produce electricity withphotovoltaic panels.

Risks of solar energy.

CFC gases destroy the ozone in the ozonosphere.Ozone is important because it filters harmful ultravioletlight before it reaches the Earth’s surface.

Carbon dioxide and other gases produce thegreenhouse effect.

However, the recent increase of these gases in the atmosphere causes global warming, that is, an increase in global temperatures.

Track 15

Unit 8. Page 92

What happens in each part of a river?Look carefully at the illustration of the river. Listen andsay upper course, middle course, or, lower course.

• Rivers flow slowly in this part.

• This is the part where you can find deep bendscalled meanders.

• In this part, rivers flow fast. Erosion andtransportation are the dominant processes.

• In this part, deposition is dominant, so the valleyflattens out.

• In this part, the velocity of the water decreases.Transportation is dominant.

• Valleys are steep and narrow here.

Track 16


External dynamics of the EarthWeathering.

There are three types of weathering:

• Mechanical weathering, which breaks rocks byphysical forces.

• Chemical weathering, which decomposes rocksby chemical reactions.

• Biological weathering, which breaks down rocksby the action of living things.

Erosion, transportation and deposition.

• Erosion moves weathered pieces of rocks to adifferent place.

• Transportation moves eroded rock material alongsurfaces or in suspension.

• Deposition deposits moving rock materials. Thisoccurs when there is a decrease in energy in thetransportation process.

Shaping of the landscape.

• Wind may erode, transport and deposit rockmaterials to change the landscape. Wind is onlyan effective agent in places where it is strong,usually in dry regions with scarce vegetation.

• Glaciers are masses of moving ice. They cut U-shaped valleys known as glacial valleys.

• Rivers also carry out erosion, transportation and deposition, which change the landscape.The dominant process depends on the velocity of the water.

• Rainwater is a very effective agent for erodingand shaping relief features in areas with dryclimates and torrential rain.

• Groundwater causes the dissolution of limestonerock, and forms karst landscapes.

• Ocean waves, tides, and currents shape coastallandscapes.

Formation of sedimentary rocks.

Sedimentary rock is formed from sediments by the following processes: sedimentation; compaction;and cementation.

Track 17

Unit 9. Page 102

How much do you know about earthquakes?

Listen and identify the definitions: earthquake, Richter Scale, tsunami, seismic wave, hypocentre,epicentre.

• The origin of an earthquake, from where theseismic waves travel, is called the…

• This scale, numbered from 1-10, reflects theamount of energy released at the hypocentre of an earthquake.

UNIT 9

UNIT 8


• Energy released during an earthquake can causethis huge wave, which floods coastal areas.

• This is a violent trembling of the Earth’s crustwhich lasts a short time and varies in intensity.

• Energy from an earthquake travels sphericallyoutward in these sort of waves.

• This is the point on the surface of the Earth,directly above the hypocentre.

Track 18


Internal dynamics of the EarthInternal dynamics is the study of phenomena causedby the internal energy of our planet.

Earthquakes. An earthquake is a violent trembling ofthe Earth’s crust which lasts a short time and varies in intensity.

Volcanic eruptions. Magma is expelled to the exteriorthrough a volcano. When magma erupts through theEarth’s surface, it is called lava.

Measures to control catastrophic damage.

• Prediction. This includes studying the probabilityof damage by earthquakes and volcanoes.

• Preparedness. This includes the safety measuresadopted to minimize damages in the event of a disaster.

Rocks.

Igneous rocks are formed by the cooling and solidifyingof magma. There are two types of igneous rock:

• Volcanic or extrusive igneous rocks. These areformed when lava cools and solidifies quickly,at the Earth’s surface.

• Plutonic or intrusive igneous rocks. These areformed when magma cools and solidifies slowly,within the Earth.

• Metamorphic rocks. These are formed from thetransformation of other rocks due to increases in temperature or pressure, or both at the sametime.

Track 19

Unit 10. Page 111

How much do you know about energy?Listen to these statements about energy. Then say trueor false.

• Energy is a physical quantity which produces a change or an effect.

• Energy is measured in kelvins.

• Chemical energy is contained in electromagneticwaves.

• Thermal energy is energy released in the form of heat.

• One type of energy can be transformed intoanother type of energy.

• Electromagnetic energy travels through a wirecircuit.

• Electromagnetic energy is energy stored in electromagnetic waves or radiation.

• Electrical energy is produced by the flow of electric charge.

• Energy is measured in joules in the InternationalSystem.

Track 20


EnergyEnergy is the ability to do work. It is a physical quantitywhich produces a change or effect.

There are different types of energy: mechanical;electrical; chemical; thermal; nuclear, and electromagnetic.

Energy can change from one type to another.

Non-renewable energy sources.

Non-renewable energy sources are used up faster thanthey can be replenished. One day they will run out.

Non-renewable energy sources include coal, oil,natural gas and uranium.

Fossil fuels were formed by the remains ofmicroorganisms, plants and animals buried millions of years ago. They were transformed by the effects of heat, pressure and bacteria, over time.

• Coal. Coal is used to generate electricity, heat,and to make steel.

• Oil. Oil is used to generate electricity. It is alsoused to produce automobile fuel and manychemical products.

• Natural gas. Natural gas is used to generateelectricity and heat.

• Uranium. Uranium is used in nuclear powerstations to produce electricity and heat.

Renewable energy sources.

These energy sources are replenished continuously,and naturally. There are several types of renewableenergy sources: solar, eolic, hydroelectric, geothermal,biomass, and tidal.

• Solar energy uses sunlight to produce heat and electricity.

UNIT 10


• Eolic energy uses wind to produce electricity.

• Hydroelectric energy uses moving water to produce electricity

• Biomass energy comes from organic materialfrom plants and animals.

• Geothermal energy uses heat stored beneath the Earth’s surface.

• Tidal energy is produced by tidal movement.

Track 21

Unit 11. Page 126

How does heat transfer?Listen to these statements about the way heattransfers. Then choose the correct answer, a. or b.

• Heat transfers by conduction, convection andradiation.

Which heat transfer can be transmitted throughspace?

a. Radiation, or b. Convection?

• Conduction occurs in solids. Heat is transferredby direct contact.

In which direction does the heat flow?

a. Heat flows from the cooler substance to thewarmer one, or b. Heat flows from the warmersubstance to the cooler one?

• Conductors are substances which allow heat tomove through them easily.

Which of these materials is a good conductor?

a. Metal, or b. Cork?

• Insulators do not allow heat to move throughthem easily.

Which of these materials is a good insulator?

a. Iron, or b. Plastic?

• In convection, heat is transferred by themovement of currents.

Which statement is correct.

a. Convection only occurs in solids,

b. Convection only occurs in liquids and gases.

• Radiation is the transfer of heat byelectromagnetic waves.

Which statement is correct:

a. Radiation is the fastest form of heat transfer,

b. Radiation is the slowest form of heat transfer.

Track 22


Heat and Temperature

Heat.Heat is the amount of thermal energy that istransferred from one body or system to another, due toa difference in temperature.Measurement. In the International System, heat ismeasured in joules. Calories are also used. 1 joule isequivalent to 0.24 calories.The main effects of heat are:

• Expansion. This is the increase in volume thatoccurs when a system gains heat. Particles movefaster, and occupy more space. In general, gasesexpand more than liquids, and liquids expandmore than solids.

• Contraction. This is the decrease in volume thatoccurs when a system loses heat. Particles movemore slowly, and occupy less space.

Changes of state.Heat changes can be:

• Endothermic, when they are produced by heatabsorption.

• Or exothermic, when they are produced by heatloss.

Transfer of heat.Heat transfers by:

• Conduction. This is the transfer of heat in mostsolids.

• Convection. This is the transfer of heat in liquidsand gases.

• Radiation. This is the transfer of heat byelectromagnetic waves. No contact is necessarybetween the source and the heated substance.

Temperature.Temperature is the amount of heat in a system.Measurement. A thermometer is an instrument whichmeasures the temperature of a system quantitatively.Temperature is measured in three scales:

• The Celsius scale. This is the most commonscale. The freezing point of water is 0º Celcius,and the boiling point is 100º Celcius.

• The Fahrenheit scale. This scale was used inEnglish-speaking countries. Today, it is only usedin a few countries for non-scientific purposes.The freezing point of water is 32º Fahrenheit,and the boiling point is 212º Fahrenheit.

• The Kelvin or absolute scale. This scale is usedby scientists. The freezing point of water is 273kelvin and the boiling point is 373 kelvin. TheInternational System uses the Kelvin scale.

UNIT 11


Track 23

Unit 12. Page 132

How much do you know about light?Listen to these statements about the property of light.

Then say if they are true or false.

• Light travels in waves and does not require a medium.

True or false?

• The speed of light is 300,000 metres per second.

True or false?

• Reflected light is light which hits a surface,bounces off and begins to travel in a differentdirection.

True or false?

• Now, look at the diagram of how light isreflected. The reflected ray hits the surface.

True or false?

• The angle of incidence is the same as the angleof reflection.

True or false?

• Reflections are more noticeable when thesurface is rough.

True or false?

Track 24


Light and soundLight.

Light is a form of energy. Light allows us to see thecolours and shapes of objects. Depending on how lighttravels through them, objects can be transparent,translucent or opaque.

The properties of light.

• Light travels in a straight line.

• The speed of light depends on the medium. In a vacuum and in the air, the speed of light isapproximately the same, that is, 300,000 km per second.

Reflection.

Light is reflected when a ray of light, called theincident ray, hits a surface, then changes direction.When the incident ray changes direction, it is calledthe reflected ray.

Refraction.

Light is refracted when it passes from one medium to another with a different density.

A lens is a glass or plastic disc with one or two curvedfaces. There are two kinds of lenses:

• Converging lenses, which concentrate the rays of light.

• Diverging lenses, which disperse the rays of light.

Sound.

Sound is a form of mechanical energy produced by thevibration of an object.

The properties of sound.

• Sound needs a material medium to be able totravel.

• Sound cannot travel in a vacuum.

• The speed of sound depends on the medium.

• In air, the speed of sound is 340 metres persecond.

The qualities of sound.

• Intensity. Intensity depends on the amplitude of the sound waves.

• Pitch. Pitch depends on the frequency of thesound waves

• Tone. Tone allows us to identify the source of a sound which has the same frequency and intensity.

Reflection.

• Sound is reflected when a sound wave meets an obstacle. The sound wave bounces off, and changes direction.

• The reflection of sound causes two phenomena:echoes, and reverberation.

UNIT 12

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