Topic 4 - Waves Flashcards
Waves transfer ___ and ___ but do not transfer ___
Waves transfer Energy and information but do not transfer matter.
What are the two types of waves?
Transverse
Longitudinal
What is 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
1) electromagnetic waves
2) seismic s-waves
Give two examples of longitudinal waves
1) sound waves
2) seismic p-waves
What are the two parts of a longitudinal wave called?
Compression and rarefactions
What are the two parts of a transverse wave called?
Peaks and troughs
What is a wave’s amplitude?
The maximum displacement of a point on a wave from its undisturbed point
What is wavelength?
The distance from a point on a wave to the same position on the adjacent wave.
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, Hz
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 the transferred through a medium.
What does a wave transfer?
Energy
State the equation used to calculate wave speed.
Wave speed = frequency x wavelength
Speed(m/s) = frequency (Hz) x Wavelength (m)
What is meant by the period of the wave? What’s the equation
The length of time it takes for one full wave to pass through a point.
T = 1/frequency
Second = 1/Hz
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 (the Angle it comes in at) is the same as the angle of reflection (the angle it leaves at).
What is refraction?
Refraction is the change in speed of a wave as it reaches a boundary between two media, usually resulting in a change in direction (if it enters at an angle).
What occurs when light is refracted at a boundary?
The light changes speed and direction in the new medium.
If the new medium is more dense, the light will travel slower and bend towards the normal.
If the new medium is less dense, the light will travel faster and bend away from the normal.
When entering a denser material/medium, light waves
Slow down and bends towards the normal.
When entering a less dense material, light waves
Speeds up and bend away from the normal
How can refraction be measured?
The angle of incidence, i, and angle of of refraction, r, can be measured and compared. All angles are measured relative to the normal.
What are the effects of absorption the of different wavelengths of waves in different mediums?
Some material behave differently depending on the wavelength
An example is glass which will transmit visible light, but reflect UV light.
How do sound waves travel through a solid?
The particles in the solid vibrate and transfer KE through the material.
How does the human ear work?
1) The outer ear collects the sound which travels into the ear
2) The sound waves cause the eardrum to vibrate at the same frequency.
3) This is amplified by three ossicles (small bones)
4) This causes the hair in the cochlea to vibrate
5) The cochlea converts the vibrations into electrical signals
6) The signals are passed to the brain through auditory nerve
7) Brain converts the electrical signals into sound
What is the frequency range of human hearing?
20Hz - 20kHz
1kHz = 1000Hz
What is an ultrasound wave?
A sound wave with a frequency greater than 20,000Hz
What is sound of frequencies less than 20Hz called?
Infrasound
What natural event causes seismic waves to be produced. What types are produced?
Earthquakes
They produced both P-waves and S-waves
A P waves transverse or longitudinal?
Longitudinal
Are S waves transverse or longitudinal?
Transverse
State a difference between the mediums that P-waves and S-waves can travel through.
P-waves travel through both solids and liquids
S-waves only travel through solids (not liquids)
What is the significance of P and S waves?
The provide evidence that the Earth has a liquid core; only P waves produced by an earthquake can be detected on other side of the globe.
What technique is used to detect objects in deep water and measure water depth?
Echo sounding
High frequency sound waves are emitted, reflected and detected.
Time difference between emission and detectors alongside wave speed, are used to calculate distances.
How does Sonar work?
When ultrasound waves are emitted they reflect off boundaries and their echoes are detected.
The speed of the ultrasound is known and also the time it takes detect the echoes
The equation distance = speed x time is used find the distance and travelled
The distance travelled is halved to give the distance between emitter and boundary (as the wave had to travel there and back)
How does foetal scanning work?
An ultrasound wave is sent into the patient’s body. It passes through the body and reflects off the organs and tissue.
The device then uses the reflected ultrasound waves to produce an image of the foetus.
Ultrasound is safe and therefore does not damage cells.
