u12 light sound

ESSENTIAL NATURAL SCIENCE 2Unit 12

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Light and sound

CONTENTS

RESOURCES



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Contents

Sound

Sound as waves Properties

Qualities

The qualities of sound

Reflection

Echoes and reverberationSonar

Light and sound

Perception

The ear

Light

Light as wavesLight sourcesLight and objects

Properties

How light travels

Shadows

Types of shadowsEclipses

Reflection

How light is reflectedMirrors

Refraction

How light is refractedLenses

Colour

Seeing coloursMaking colours

Perception

The eyeCameras



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Eclipses

Resources

Light and sound as waves

Light sources Light and objects How light travels Shadows

How light is reflected

Mirrors LensesHow light is refracted

Seeing colours Making colours The eye Properties of sound

Echoes and reveberations

The earSonarThe qualities of sound

Cameras

Links

Light and sound



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Light waves

Light and sound as waves

Sound waves

wavelength

trough

crest

Wave characteristics Units of measurement

frequency hertz (Hz)

wavelength metre (m)

Light and sound travel in waves.



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Light sources

Sun

stars

Artificial sources

light bulb

candle

torch

Light is a form of electromagnetic energy. Natural sources



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Light and objects

Transparent

They allow light to travel through.

Translucent

They absorb some light, and they allow some to travel through.

Opaque

They do not allow light to travel through.

Objects, materials and substances can be:



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How light travels

ray of lightbeam of light

Light travels in a straight line.

Light travels at a speed of about 300,000 km/s in a vacuum and in air.

Light travels through the small holes if these holes are aligned.



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Shadowsshadow

shadow

penumbra



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Eclipses

SEE ANIMATION

Solar eclipseLunar eclipse

Solar eclipse



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Eclipses

Solar eclipseLunar eclipse

Solar eclipse

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The incident ray hits the surface. The reflected ray bounces off the surface.

incident ray

reflected ray

The light bounces.



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The incident ray hits the surface. The reflected ray bounces off the surface.

incident ray

reflected ray

The light bounces.

normal ray

reflecting surface

angle of incidence

angle of refection

incident ray reflected ray



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Mirrors

Concave mirror

Convex mirror

Spherical or curved mirrors

Flat mirrors

Symmetrical images



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

water

pencil

refracted light

How light is refracted

Light bends at the boundary of two media.



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Lenses

Converging lens

It concentrates the rays of light.

Diverging lens

It disperses the rays of light.



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Seeing colours

Prism

Range of wavelengths

Visible light

Ult

ravi

ole

t lig

ht In

fared lig

ht

Visible light waves are the only electromagnetic waves visible to the human eye.



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Making colours

Colours of light

Colours of pigment

red

greenblue

yellow

magenta

cyan

white light

Objects reflect the colour of light that we can see and absorb all the other colours.

Colour mixing



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The eye

Light enters through the cornea

The iris regulates the amount of light that enters.

The pupil increases or decreases depending on the amount of light.

An inverted image forms on the retina

The optic nerve transmits the image to the brain.

The lens focuses images.

HOW A CAMERA WORKS



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Cameras

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Light enters through the shutter.

The lens focuses images.

The image forms on the film or sensor.

The diaphragm regulates the amount of light that enters.



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Properties of sound

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



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Properties of sound

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

THE SPEED OF SOUND IN DIFFERENT MEDIA

Air (at 20 ºC) 340 m/s

Water (at 0 ºC) 1,500 m/s

Iron (at 20 ºC) 5 ,130 m/s



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Intensity depends on the amplitude of the sound waves.

Pitch depends on the frequency of the sound waves.

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

soft sound

loud sound

low pitched sound

high pitched sound

SEE INTENSITITES OF SOME SOUNDS.

CLICK ON THE SOUND ICON TO LISTEN TO THE SOUND.



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Intensity depends on the amplitude of the sound waves.

Pitch depends on the frequency of the sound waves.

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

soft sound

loud sound

low pitched sound

high pitched sound

SEE INTENSITITES OF SOME SOUNDS.

CLICK ON THE SOUND ICON TO LISTEN TO THE SOUND.

Intensity of some sounds

Leaves rustling 20 dB

Whispering 30 dB

Inside a library 40 dB

Inside an office 50 dB

Normal conversation 60 dB

City traffic 80 dB

Motorcycle 90 dB

Rock concert 110 dB

Thunder 120 dB

Jet taking off 140 dB

Rocket blasting off 180 dB



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Echoes and reverberations

Distance (metres)

0 0.1

34 0

Time (seconds)

17

Speed: 340 m/s

ECHO REVERBERATION

An echo is heard at more than 17 metres.

A reverberation is heard at less than 17 metres.



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Sonar

Fishing boats use sonar to detect shoals of fish.

reflected sound

emitted sound



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The ear

Frequency (Hz)

Infrasound(below 20 Hz)

Ultrasound (above 20,000 Hz)

The ear can hear sounds which have a frequency of 20 Hz to 20,000 Hz.

sound wave

The eardrum vibrates when sound waves reach it.



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Links

Sound energyhttp://www.worsleyschool.net/science/files/sound/energy.html

What is soundhttp://antonine-education.co.uk/Physics_GCSE/Unit_3/Topic_5/topic_5.htm

Soundhttp://www.bbc.co.uk/schools/ks3bitesize/science/physics/sound_intro.shtml

Light, reflection & refractionhttp://acept.asu.edu/PiN/mod/light/reflection/pattLight1.html

Light and opticshttp://camillasenior.homestead.com/optics.html

Light activitieshttp://galileo.phys.virginia.edu/classes/620/Optics_Activities.html

Materials and lighthttp://jc-schools.net/write/sci/light_files/frame.htm

Optics for kidshttp://www.opticalres.com/kidoptx_f.html

Light and soundhttp://www.sciencejoywagon.com/physicszone/09waves/

u12 light sound

Business

light waves light

properties of sound

waves light sources

eye light

colour of light

cameras light

light bends

reflected sound emitted