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Name ________________ Nº___

Surname __________________________

NATURAL SCIENCE

UNIT 7. LIGHT AND HEAT

Exam Date: __________________

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UNIT 7. LIGHT AND HEAT In this unit we are going to learn about:

1. Light - Light sources: natural and artificial. - Composition of light - Properties of light: Speed, colour, and direction - Light and materials - Reflection and refraction of light

2. Heat and temperature - Heat and Temperature - Effects of thermal energy: melting, evaporation, and expansion - Materials and heat: Conductors and insulators

Science Investigators

Do you have any other questions? Write them down and let’s find the answer

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Why do ice creams melt?

Why does the soup in my plate get cold?

Why are pans made of metal?

Why do we see the rainbow?

Why are winter clothes made of wool?

Why do we see a spoon bent in

a glass of water?

Can animals emit light?

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1. LIGHT

Light may come from:

• Natural sources like the Sun or other stars of fire. Some

animals like fireflies, glow warms or deep-sea fish, can also

emir light.

• Man-made sources, like light bulbs, candles and laser beams.

COMPOSITION OF LIGHT Isaac Newton discovered that sunlight, also known as

visible light or white light, is made up of 7 different colours.

When the Sun shines and it rains at the same times, we see

a rainbow. This is because the raindrops act as tiny prisms

that separate light into seven colours: red, orange, yellow,

green, blue, indigo and violet.

PROPERTIES OF LIGHT

The main properties of light are:

1. Light travels at 300,000 kilometres per second in space, but when it travels through

materials such as water, air or glass it travels at a lower speed. It is faster than

anything else that we can observe in the Universe. It still takes over eight minutes

for light from the Sun to reach the Earth.

2. Light travels in a straight line. When light encounters

an obstacle in its way, the obstacle blocks the light

and causes a shadow.

3. Light travels in all directions. That’s why when we turn on a light, the whole room

lights up.

Light is a form of energy that allows us to see everything around us.

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LIGHT AND MATERIALS Light behaves in different ways depending on the material it interacts with. Light can pass

through some types of matter, whereas other types do not let light through.

Based on this criterion, different materials can be classified as transparent, translucent or

opaque.

• Transparent objects. Light passes easily through them.

Objects on the other side can be seen easily. Water,

air and glass are all transparent materials.

• Translucent objects. Only some light can pass through

them. Objects on the other side appear blurry. Plastics

and fog are translucent materials.

• Opaque objects. Light cannot pass through them. A

shadow forms on the other side. We cannot see

through these materials. Wood, lead, iron, mirrors and

many rocks are opaque.

REFLECTION AND REFRACTION OF LIGHT 1. REFLECTION

Reflected light allows us to see everything. Almost all

objects that are not light sources reflect some light. Some

of this reflected light enters our eyes, which allows us to

see the reflecting objects. For example, we see the Moon

because it reflects light from the Sun. Light hits an object. The object reflects the light. This reflected light enters your eyes.

When light hits an object, it bounces off the object

and changes direction. This is called reflection.

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When light hits a smooth surface all the rays reflect in the same direction. When it hits

a rough surface, the rays reflect in different directions

Smooth surface Rough surface

Most objects only reflect part of the light that hits their

surface. However, smooth and shiny surfaces, like mirrors,

reflect most of light. Light hitting a mirror is reflected at an

equal angle.

THE COLOUR OF OBJECTS

When light reaches an object, some of the colours of light

are absorbed, and other are reflected. For example, when

we see a blue object, it appears blue because it absorbs all

other colours of light and reflects blue. It is blue light that

reaches our eyes. Therefore, the colour we see in an object

is the colour of light that the object reflects. The object

absorbs all the other colours that make up the white light.

White objects do not absorb any colour of light; they reflect all light.

Black objects absorb all colours of light; they do not reflect any light.

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2. REFRACTION

Refraction occurs when light changes direction because it passes

from one substance to another with different densities.

For example, refraction can be observed when light passes from

air to water at an angle, because water is denser than air.

LENSES

Lenses are pieces of curved glass or plastic that refract light. They are used in

microscopes, glasses, magnifying glasses, telescopes, binoculars and cameras.

Lenses can make objects look bigger or smaller depending on the shape of the

lens and on the way they refract light.

They can be convex or concave.

• Convex (Converging) lenses are thicker in the middle and bring together the rays

of light. Like the ones in magnifying glasses, make the objects we see through

them look bigger.

• Concave (Diverging) lenses are thinner in the centre and spread out the rays of

light. Like the ones in glasses to correct short-sightedness, make the objects we

see through them look smaller.

What we see here is a called refraction, or the bending of

light. When light passes through transparent objects, it

refracts or bends. When the glass is full of water, it acts as

a cylindrical convex lens, and produces an inverted image.

The inverted image may appear larger, smaller or the same

size, depending on where you position the paper, the glass, and your viewpoint. Another

variable is the size (diameter) of the glass.

When light passes from one material to another material with a different density,

it bends where the two surfaces meet. This is called refraction.

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2. HEAT AND TEMPERATURE

HEAT

Heat is the transfer of thermal energy from something hotter to something cooler. For

example, if we touch a hot plate, thermal energy goes from the plate to our skin, so our

skin gets hotter.

Heat can be transferred in the following ways:

• By contact: If we put a pan of cold water on a fire, the heat from

the fire transfers firstly to the pan and then to the water and the

water becomes hot.

• At a distance: We can feel the heat from the Sun or from a flame

without touching it.

This flow of energy causes changes. When we heat an object, we add thermal energy.

When we add thermal energy to an object, one of two

things can happen: the temperature of the object increases

or the substance changes state. For example, ice cream

melts because there is a transfer of energy from the warmer

air to the cooler ice cream.

TEMPERATURE

Temperature isn’t the same as heat. Temperature is the measurement of how hot or cold

something is. In order to know the temperature of an object, we use thermometers.

Temperature is measured in degrees Celsius (ºC). On the Celsius scale, water freezes at

0ºC and boils at 100ºC. The average temperature of the human body is 37ºC.

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EFFECTS OF THERMAL ENERGY

TEMPERATURE INCREASE

When two objects at different temperatures come into contact, heat goes from the hotter

object to the cooler object until both reach the same temperature. This flow of thermal

energy is called heat.

For example, if we leave a cup of hot chocolate on a table, heat goes from the hot drink

into the air until both reach the same temperature. In the same way, when we touch

something hot, thermal energy transfers from the object to our hand. When we touch

something cold, thermal energy transfers from our hand to the object.

CHANGE OF STATE

A change in the thermal energy of a substance can also make the substance change state.

If the thermal energy in a solid increases, it may become a liquid. This process is called

melting. If the thermal energy of a liquid increases, it may become a gas. This process is

called evaporation. If the thermal energy of a gas increases, the gas particles move faster

and collide harder and more frequently with each other. This can make the gas expand.

EXPANSION AND CONTRACTION Materials expand, or get bigger, when their temperature increases. They

contract, or get smaller, when their temperature decreases.

Railways and bridges are built with expansion joints so

that the parts have room to expand and contract. In the

past, expansion joints were not used. The materials

expanded and contracted, and

this caused a lot of cracks.

Water is a special case because it increases in size when it freezes!

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HEAT TRANSMISSION

Depending on how they transmit heat, materials can be classified into two types:

• These are materials that transmit heat quickly and effectively. Metals

(iron, cooper or alumninium) are good heat conductors. That's why,

many pots and pans are made of metal.

CONDUCTORS

• These are materials that transmit heat very slowly. Cork, glass, plastic,

wood and wool are good heat insulators. For example, many winter

clothes are made of wool, so heat does not pass from our bodies to the

colder air around us so that we stay warm.

INSULATORS

The metal pot transmits heat to the food. The handle is made of wood, an insulator, so we do not burn ourselves.

Double windows help to save energy in houses, Glass and air are good thermal insulators, and they prevent heat loss.

Some modern materials, such as polystyrene, are good heat insulators as well because they contain a lot of air.

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In this unit I have learned:

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I would like to learn more about:

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REFERENCES BOOKS

• Science 5 Primary, sm, 2009.

• Science The world around us 5 Primary Education. Anaya English, 2013.

• Science The world around us 6 Primary Education. Anaya English, 2013.

• Natural and Social Science Primary 5 Pupil’s book Macmillan, 2012.

• Natural Science 5 Primary Student’s book. edebé, 2015.

• Natural Science 5 Primary Activity Book. edebé, 2015 .

• Natural Science. Primary 5 Anaya English- ANAYA, 2014.

• Natural Science. Primary 6 Anaya English- ANAYA, 2015.

• Natural Science. Primary 5 (Activity Book) Anaya English- ANAYA, 2014.

• Social and Natural Sciences 5 Look and Think Oxford Education, 2010.

• Natural Science 5 (Comunidad de Madrid) Vicens Vivens, 2015.

• Natural Science Our World (Comunidad de Madrid) Richmond, 2015.

• Natural Science Primary 5 (Comunidad de Madrid) ByME Macmillan & Edelvives, 2015.

• Top Science 5 Primary. Ed Santillana/ Richmond, 2011.

• Top Science 6 Primary. Ed Santillana/ Richmond, 2011.

• Science “My World” Primary 6, Edelvives, 2013.

• Natural Science Primary Brilliant Ideas. ANAYA, 2018

WEBS • https://gosciencekids.com/refraction-light-glass-water-play-steam-kids/ • https://www.dkfindout.com/us/science/heat/ • https://www.dkfindout.com/us/science/light/ • https://mocomi.com/speed-of-light/ • https://mocomi.com/reflection-and-refraction-of-light/ • https://mocomi.com/how-do-we-see-color/ • https://mocomi.com/discovery-of-light/ • https://www.brainpop.com/science/energy/light/ • https://www.brainpop.com/science/energy/heat/ • https://www.ducksters.com/science/light.php • https://www.sciencekids.co.nz/light.html • https://www.sciencekids.co.nz/light.html • https://www.ducksters.com/science/heat.php • https://www.coolkidfacts.com/heat/ • https://www.scienceforkidsclub.com/heat-facts.html • https://kids.kiddle.co/Heat