Transcript Light and Sound

Sound and Light
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Yr 8 Science
In This Topic you should be
able to:
Describe and identify energy changes in
situations involving light and sound
 Describe sound as a form of energy
requiring a medium (matter) to travel
through
 Describe light energy as a form of
energy requiring a no medium to travel
through

Explain the difference between a noise
and a musical note
 Describe how musical instruments work
and how music is recorded
 Explain the difference between
reflection and refraction
 Understand how lenses work
 Explain why objects have colour

Facts!
More than 90% of the information we
receive reaches our senses as a type of
energy detected by our eyes (light
energy) or ears (sound energy).
 It takes 8 minutes for the light to travel
from the sun to Earth but only a
millionth of a second to travel a football
field.

Measuring sound

Try these things at home
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Measuring Sound
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The frequency of sound (measured in Hertz)
is also called the pitch.
 An example of a high pitched sound
________________
 An example of a low pitched sound
________________
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This frequency is a measure of the vibrations
per second. A sound with a high pitch has
more vibrations and the waves are closer
together!
 http://www.youtube.com/watch?v=lKaQzgwxy
Vg - Octave Wave Forms
Mozzie Ringtones
Your teacher will play a variety of
frequencies starting at 8000 hertz and
increasing to 18,000 hertz.
 List each frequency and tick whether
you can hear it.

E.g.
 8000 Hz
 18,000 Hz
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The speed that sound travels at is much
slower than (about 1/3rd km a second)
that of light (300,000 km a second).

A timer who stands a long way from the
starter’s gun will start timing when he
sees smoke rather than listening to the
sound. Can you think of another
example of when we see something and
hear the associated sound after?
We often hear thunder after the
lightening even though they occur at the
same time!
 Every 3 seconds you count between
thunder and lightening, tells you that the
lightening struck a km away
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The Sound of music
Noise is a jumble of many sounds.
 Musical notes are more regular sounds
that are pleasing to the ears.
 These are controlled vibrations in
musical instruments.
 Every musical instruments produces
vibrations and has a resonator to
produce longer sounds.

Musical instruments

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Choose an instrument
Prepare a one page report on how it operates
(This can be done in pairs but each student
must write a report)
Include:
 A Diagram
 Detailed description of the parts
 How sound is produced
 Which parts vibrate and which parts resonate
 How the pitch of a note is changed
 The frequency range
 How the volume is controlled
 How to tune the instrument
Brainstorm: what instruments
do you know? What
categories?

Percussion
Drums,

bongos, cymbals, Triangle, clap sticks, chimes
Strings
Guitar,
violin, cello, banjo, piano, bouzki, bass guitar
 Wind
Flute, trumpet, trombone, didgeridoo, bagpipes, piccolo,
BENDING AND BOUNCING
LIGHT EXPERIMENT
What happens when light meets
different substances?
 Clear glass
 Frosted glass
 Wood

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Equipment: A ray box, materials (above)
Results
Substance
Clear Glass
Frosted
Glass
Wood
What you
can see
through the
substance?
What
happened to
the Beam of
light?
Conclusion

When light travels through clear glass the
beam remains on the same path and is not
scattered.
 When light hits wood it is absorbed, however
some light must be reflected because we can
see it.
 When light travels through frosted glass it lost
intensity (some light was blocked) and the
light was scattered and bent off its original
path.
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Electromagnetic Spectrum
Visible light is part of the
Electromagnetic spectrum
 All light EM waves travel at the speed of
light
 The Wavelength is the distance
between two crests of the waves
 The Amplitudes is the height of the
wave.

Benefits and Dangers!

What do we uses EM waves for?
-Transmitting sound and picture signals on Radio waves
eg TV’s and Radios.
- Heating food in a microwave
- Seeing broken bones in an X-ray
-Keeping warm using heaters and flames which
project infrared rays

What are the dangers of EM waves?
-Long term exposure to X-rays or Gamma Rays can
cause cancers
-Skin cancers including melanomas are caused
by UV Rays
How a Camera works
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Thinking activity
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Using these facts and the diagram of a
camera describe how you think a simple
camera works:
Film is coated in a light-sensitive chemical
that changes colour when exposed to light
 A lens is a curved piece of glass or plastic
which focuses light into a single point
 A shutter in a camera moves very quickly
allowing only a split-second exposure to light
 Every thing we can see has light reflecting off
of it.
Negatives
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What do you notice on these negatives?
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PHOTOGRAPHS
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Negatives- The original film material which
shows light parts of a photo dark and vice
versa. Silver Nitrate crystals go dark when
they are exposed to light.
 An aperture is the size of the hole which
allows light into a camera.
 If a photo has too much light let through the
aperture it is considered as over-exposed
 If a photo is too dull and has too little light
coming through its aperture we call it underexposed.
In 1666, Isaac Newton discovered that
white (visible light) was made up of a
spectrum of colours (the rainbow or
ROYGBIV)
 When light was passed through a
triangular prism he demonstrated this
spectrum.

Light through a prism
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What is occurring when we see green
grass?
 What about when light travels through a
coloured translucent material like red
cellophane?
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