Topic 4 - waves Flashcards
What do waves transfer?
Energy and information
What are the two types of waves?
Transverse
Longitudinal
What is a transverse wave?
A wave for which the oscillations are perpendicular to the direction of energy transfer
What is a longitudinal wave?
A wave for which the oscillations are parallel to the direction of energy transfer
Give two examples of transverse waves
Seismic S-waves
Electromagnetic
Give two examples of longitudinal waves
Sound waves
Seismic P-waves
What are the two parts of a longitudinal wave called?
Compressions and rarefactions
What are the two parts of a transverse wave called?
Peaked and troughs
What is a wave’s amplitude?
The maximum displacement of a point on a wave from its undisturbed position
What is wavelength?
The distance from a pint on.a wave to the same position of the adjacent wave
Most commonly peak to peak or trough to trough
What is the frequency of a wave?
The number of waves that pass a given point each second
What is the unit used for frequency?
Hertz
What is meant by a frequency of 200Hz?
200 waves pass a given point each second
What is wave speed?
The speed at which energy is transferred through a medium
What is wave velocity?
The product of the wavelength and frequency of the wave
What is the equation to calculate wave speed?
Frequency x wavelength
What is meant by the period of the wave?
The length of time it takes for one full wave to pass through a point
What word is used to describe when a wave bounces off a surface?
Reflection
What is the normal (in terms of reflection and refraction)?
A vertical imaginary line which is perpendicular to the boundary
What occurs when light is reflected off a boundary?
It bounces off a smooth flat surface so that the angle of incidence is the same as the angle of reflection
What is refraction?
The change in speed of a wave as it reaches a boundary between two media, usually resulting in a change in direction
What occurs when a light is refracted at a boundary?
The light changes speed and direction in the new medium
When entering a denser medium, light waves…
Slow down and bend towards the normal
When entering a less dense medium, light waves…
Speed up and bend away from the normal
How can refraction be measured?
The angle of incidence and the angle of refraction can be measured and compared
What are the effects of absorption of different wavelengths of waves in different mediums?
Some materials behave differently depending on the wavelength
How do sound waves travel through a solid?
The particles in the solid vibrate and transfer kinetic energy through the material
How does the human ear work?
The outer ear collects the sound which travels into the ear
The sound waves cause the eardrum to vibrate at the same frequency
This is amplified by three ossicles
This causes the hair in the cochlea to vibrate
The cochlea converts the vibrations into electrical signals
The signals are passed to brain through auditory nerve
The brain converts the electrical signals into sound
What is the frequency range of human hearing?
20Hz - 20kHz
What is an ultrasound wave?
A sound wave with a frequency greater than 20,000 Hz
What is sound of frequencies less than 20Hzcalled?
Infrasound
What natural event causes deistic waves to be produced? What types are produced?
Earthquakes
They produce both P-waves and S-waves
Are P waves transverse of longitudinal?
Longitudinal
Are S waves transverse of longitudinal?
Transverse
What mediums can P waves travel through?
Both solids and liquids
What medium canS waves travel through?
Only solids
What is the significance of P and S waves?
They provide evidence that the Earth has a liquid core; only P waves produced by an earthquake can be detected in the other side of the globe
What technique is used to detect objects in deep water and measure water depth?
Echo sounding
How does sonar work?
When ultrasound d waves are emitted they reflect off boundaries and their echos are detected
The speed of the ultrasound is known and also the time it takes to detect the echos
The equation: distance = speed x time is used to find the distance travelled
The distance travelled is halved to give the distance between emitted and boundary
How does foetal scanning work?
An untranslated d wave is sent into the patient’s body
It passes through body and reflects off the organs and tissue
The device then uses the reflected ultrasound d waves to produce and image of the foetus
Ultrasound is safe and therefore does not damage cells
