OPTICS & ACOUSTICS SUMMARY NOTES
Light and sound are both waves.
OPTICS
Light travels in straight lines called light rays.
If you shine a straight beam of light into a mirror the light is reflected.
Complete the diagram below marking on the normal, the incident ray,
the reflected ray, the angle of incidence and the angle of reflection.
mirror
The law of reflection is:
The angle of incidence is equal to the angle of reflection.
When light passes from one material to another it bends or changes direction.
This is called refraction. Complete the diagram below marking on the
normal, the incident ray, the refracted ray, the angle of incidence and the
angle of refraction.
When light goes from AIR to GLASS it bends towards the normal.
When light goes from GLASS to AIR it bends away from the normal.
Transparent materials let all light pass through them.
Translucent materials let some light pass through them.
Opaque materials let no light pass through them.
When white light is passed through a prism a spectrum is produced.
Remember ROY G. BIV
Red Orange Yellow Green Blue Indigo Violet
Complete the diagram shown
Shown on the right.
White Light
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OPTICS & ACOUSTICS SUMMARY NOTES
When white light is passed through a filter only light the same colour as the
filter passes through the filter. All other colours are absorbed.
E.g. a red filter lets only the red part of white light through. Orange,
yellow, green, blue, indigo and violet are absorbed.
Some uses of filters include: traffic lights, photography and disco lights.
The three primary colours are red, blue, and green. All of the colours we
see are made from these three colours. They mix to give the
Red
following colours
RED + GREEN = YELLOW
Magenta
Yellow
Blue
Green
RED + BLUE = MAGENTA (PINK)
BLUE + GREEN = CYAN (LIGHT BLUE)
Cyan
RED + BLUE + GREEN = WHITE
The colours we see objects depend on two things:
the colour of the object and the colour of the light shining on the object.
ACOUSTICS
Sound is caused by vibrations.
In order for sound to travel we need solids, liquids or gases.
Sound cannot travel through a vacuum. Space is a vacuum.
Bell
Connect
to
battery
Connect
to pump
When air is pumped out
of the bell jar the sound
gets quieter. When
there is no air left (a
vacuum) you will hear
no sound because
there are no particles to
vibrate.
A sound meter is used to measure the loudness of sound; this is also called
sound level.
Sound level is measured in decibels, dB.
If you are exposed to loud sounds for a long period of time your hearing can
be damaged.
Soundproofing can be used to reduce the harmful effects of sound
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OPTICS & ACOUSTICS SUMMARY NOTES
Wave diagrams
‘Starter
sound
wave’
Another word for pitch is frequency. The frequency of a wave is the
number of waves produced in a second and is measured in Hertz, Hz.
The higher the pitch the higher the frequency. You would see more waves on
the screen of an oscilloscope.
Sketch what you would see on an oscilloscope if the pitch of the ‘starter
sound wave’:
a) was higher
b) was lower
HIGH PITCH
LOW PITCH
When the loudness of a sound increases the amplitude of the wave
increases. The frequency does not change.
Sketch what you would see on an oscilloscope if the ‘starter sound wave’
a) was quieter
b) was louder
LOUD
QUIET
Ultrasound
Humans can hear sounds between the frequencies of 20Hz and 20,000Hz.
Some animals can hear or communicate in frequencies above 20,000Hz
called ultrasounds. Some examples are dogs, bats and dolphins
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