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Waves (Sound Waves (Echos (An echo is sound being reflected, Echos are…
Waves
Sound Waves
Sound waves are produced by objects vibrating. We hear these sounds when these vibrations, travelling as sound waves, reach our ear.
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Sound waves can travel through: solids, liquids and gasses but not through a vacuum as their are no particles to carry the vibrations.
Echos
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Echos are used in many circumstances for example finding fractures in metals and fishing boats detecting fish
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Pitch and frequency
If an object vibrates more quickly it produces sound of higher frequency. These sounds are heard as notes of a higher pitch
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Loudness
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If a drum is struck hard lots of energy is transferred to it. The drum skin vibrates up and down and creates regions of very compressed air molecules.
Audible Range
The average person can hear sound of frequency between 20 Hz and 20 KHz(20,000 Hz)
Some objects vibrate at frequencies higher than 20 KHz they are called ultrasounds. Objects that vibrate at below 20 Hz are called infra sounds.
Some animals, for example bats and dolphins communicate through the use of ultrasound
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EM spectrum
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Ultraviolet
UV light comes from the sun and is what causes tan. Too much UV light can also cause skin cancer and blindness
Infra-Red
All objects emit IR. The hotter the object is the more IR it will emit. Some cameras are designed to detect IR
X-rays
Pass easily through soft body tissue but not bones.Therefore they are use to take pictures of bones.
Microwaves
Used for cooking,communications and radar
Gamma Rays
Are highly penetrating rays and cause damage to living cells. The damage causes mutation to genes and can lead to cancer. They are used sterile medical equipment and to kill micro-organisations so that food will keep for longer.
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Describing waves
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The number of waves passing a particular point each second is called the frequency of the wave (f). This is measured in Hz
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Light Waves
Objects that emit light are called luminous objects. When emitted light enters our eye we see the object
Most objects, however are non-luminous and do not emit light. We see theses objects through the light they reflect
Light waves are transverse waves and like all waves can be reflected, refracted and diffracted.
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Dispersion
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The spectrum is formed because light is a mixture of colours that each travel at slightly different speeds. Therefore they are all refracted at different angles
Each colour emerges travelling in a slightly different direction. This process is called dispersion.
The speed of red light is changed the least and so has the smallest deviation. The speed of violet has changed the most so has the biggest deviation.
The Wave Equation
There is a relationship between the wavelength, the frequency and the waves speed (v) that is true for all waves
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Reflection
When waves strike a straight or flat barrier, the angle at which they the barrier is equal to the angle at which they meet the surface.
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