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P2-waves and the electromagnetic spectrum (Sound (Sound waves are caused…
P2-waves and the electromagnetic spectrum
wave basis
Waves transfer energy and information in the direction they are travelling
When waves travel though a medium, the particles of the medium vibrate and transfer energy and information between each other. But, overall the particles stay in the same place
Transverse waves
The vibrations are perpendicular (90) to the direction the wave travels in
Most waves are transverse including
All electromagnetic waves
S-waves
Ripples and waves in water
Longitudinal waves
The vibrations are parallel to the direction the wave travels
Examples
Sound waves
P-waves
They squash up and stretch out the arrangement of particles in a medium they pass through making compressions (high pressure, lots of particles) and rarefactions (low pressure, fewer particles)
Wave speed
Wave speed (m/s)= distance(m) / time (s)
Wave speed (m/s) = frequency (Hz) * wavelength(m)
Measuring waves
Using an oscilloscope to measure the speed of sound
By attaching a signal generator to a speaker you can generate sounds with a specific frequency. You can use two microphones and an oscilloscope to find the wavelength of the sound waves generate.
Measure the speed of water ripples using a strobe light
Use peak frequency to find the speed of waves in solids
You can find the speed to waves in solids by measuring the frequency of the sound waves produced when u hit the object e.g. a rod with a hammer. Hitting the rod causes waves to be produced along the rod. These waves make the rod vibrate and produce sound waves in the air around the rod (this is how percussion triangle works). Theses sound waves have the same frequencies as the waves in the rod.
Wave behaviour at boundaries
When a wave meets a boundary between 2 materials ( a material interface), 3 things can happen
The wave is absorbed by the second material
The wave transfers energy to the materials energy stores. Often the energy is transferred to a thermal energy store, which leads to heating ( this is how a microwave works)
The wave is transmitted through the second material
The wave carried on travelling through the new material. This often leads to refraction. This can be used in communications as well as in lenses of glasses and cameras.
The wave is reflected
This is where the incoming ray is neither absorbed or transmitted, but instead is ‘sent back’ away from the second material. This is how echos are created.
Sound
Sound waves are caused by vibrating objects
These vibrations are passed through the surrounding medium as a series of compressions and rarefactions
Sound waves are longitudinal waves
However not all frequencies of sound can be transferred through an object. An objects size, shape and structure determine which frequencies it can transmit
Sound travels at different speeds in different media- sound waves generally travel faster in liquids than they do in gases, and faster in solids than they do in liquids
So sound waves can refract as they enter different media.
like all waves, the frequency of sound doesn’t change when it passes from one medium into another. However the wavelength does- it gets longer when the wave speeds up, and shorter when it slows down.
Sound waves will be reflected by hard, flat surfaces. Echoes are just reflected sound waves.
Sound can’t travel in space because it’s mostly a vacuum (there are no particles to move or vibrate)
When a sound wave travels through a solid it does so by causing particles in the solid to vibrate.
