Waves (4) Flashcards
What do waves transfer?
Energy and information without matter.
What is frequency and wavelength?
Frequency is the number of complete cycles of the wave passing a point per second (Hertz).
Wavelength is the length of a full cycle of a wave (from crest to crest, trough to trough or compression to compression).
What is amplitude and period?
Amplitude is the displacement from the rest position (x-axis) to a crest or trough.
Period is the number of seconds it takes for a full cycle (1/frequency).
What is the difference between transverse and longitudinal waves?
Transverse waves have vibrations normal to the direction of the wave. Transverse waves include all EM waves, seismic S-waves and ripples and waves in water.
Longitudinal waves have vibrations parallel to the direction of the wave. They include sound and seismic P-waves. They squash up and spread out particles in the medium forming areas or compression and rarefaction.
What equations do you need to know?
wave speed (v) = frequency (f) x wavelength (lambda) wave speed (v) = distance (x)/time (t)
Describe the effects of reflection, refraction, transmission and absorption of waves.
Reflection - the wave is ‘sent back’ at an equal angle to the angle it met the interface with.
Refraction - waves travel at different speeds through different mediums; so when a wave hits a boundary it can change speed therefore changing direction. It bends towards the normal if it speeds up and away if it slows down. Frequency remains constant during refraction.
Transmission - the wave carries on travelling through the material often leading to refraction.
Absorption - the wave transfers energy to the material’ energy stores.
What is the process in which convert disturbances between sound waves and vibrations in solids?
Sound waves are caused by vibrating objects which pass vibrations onto air particles which then pass vibrations onto other air particles in a series of compressions and rarefactions. When vibrating particles hit a solid, they cause the particles in the solid to vibrate as well. Sound waves travel faster in solids.
How does the ear work?
Sound waves hit the eardrum causing it to vibrate. The vibrations are passed on to tiny bones called ossicles which amplify the vibrations. They are then passed on to the cochlea which turns the vibrations into electrical signals to be sent to the brain.
What is ultra and infrasound?
Ultrasound is sound waves with a frequency higher than 20,000 hertz.
Infrasound is sound waves with a frequency less than 20 hertz.
What are some uses of ultra and infrasound?
Sonar:
Ships use a loudspeaker which emits ultrasound to send a pulse of ultrasound into the water. The ultrasound spreads through the water and is reflected by the seabed or schools of fish. A special microphone detects the reflected waves and the sonar equipment measure the time taken for the wave to reach the boat and to find the distance in between the ship and the object.
Foetal scanning:
An ultrasound probe is placed on the woman’s skin in between a layer of gel which stops the ultrasound from being reflected by the skin. The probe emits and receives ultrasound waves reflected by different mediums in the foetus. The ultrasound machine detects the time taken to receive the pulse and displays an image.
Exploration of the Earth’s core:
Seismic P-waves can travel through solids and liquids. As they travel through the Earth, they are refracted by the different mediums and create a small shadow zone. Seismic S-waves are absorbed by solids so they for a large shadow zone. Scientists can detect how long it took for the wave to reach the area and how much it refracted showing where the structure of the Earth changes drastically.
How is the change of velocity, frequency and wavelength when sound waves are transmitted from one medium to another interrelated?
The frequency of a wave stays the same in any medium, therefore, for velocity to change, wavelength has to change. Wavelength increases when velocity increases.
