Waves Flashcards
What are transverse waves?
When the medium of a wave vibrates at right angles
What type of waves are sound waves?
Longitudinal waves
What are electromagnetic waves?
Transverse waves that do not need a medium (material) through which to travel
What is frequency?
The number of waves passing a point each second; measured in hertz (Hz)
What is period?
The length of time it takes one wave to pass a given point
What is wavelength?
The distance from a point on one wave to a point in the same position on the next wave (m) - peak to peak or trough to trough
What is amplitude?
The maximum distance of a point on the wave away from its rest position (m)
What is velocity of a wave?
The speed of the wave in the direction it is travelling (m/s)
How do you calculate wave speed (m/s)?
WAVE SPEED (M/S) = FREQUENCY (HZ) X WAVELENGTH (M)
What does the speed of a wave depend on?
The medium through which it is travelling
How can you find the speed of sound?
By measuring the time it takes for a sound to travel a certain distance:
- Measure time it takes for a wave to travel between 2 fixed points such as buoys
- Calculate speed from the time and distance between the 2 points
What is refraction?
The change in direction when light moves into a different medium
Where does refraction happen?
At the interface (boundary) between the 2 media
What is the normal line?
the line at right angles to the interface
Why does refraction happen?
Light travels at different speeds in different media, and so as light passes the interface between one medium and another it changes speed; this change in speed causes the direction of the light to change
What does the bend of light depend on in refraction?
How fast the light travels in the 2 media and the angle of the light hitting the interface
What is transmission?
When the wave passes through the material and is not absorbed/refelcted
What is absorption?
When the wave disappears as the energy it is carrying is transferred to the material
What is light from light bulbs/the Sun called?
White light, and is made up of a mixture of different frequencies of light; we see these different frequencies as different colours
What does a sound wave cause?
Changes in pressure on the surface of a solid, which causes particles in the solid to vibrate and so the disturbance is passed from the air to the solid
How do we hear things?
- Sound waves enter the ear canal
- Eardrum is a thin membrane and sound waves make it vibrate
- Vibrations passed on to tiny bones (ossicles) which amplify the vibrations (make them bigger)
- Passed on to the liquid inside the cochlea
- Tiny hairs inside the cochlea detect these vibrations and create impulses which are electrical signals
- Impulses travel along neurones in the auditory nerve and reach the brain
What is the cochlea?
A coiled tube containing a liquid
What does the cochlea to detect different sounds best?
Different thickness of the membrane at different parts of the cochlea, as different sound waves are detected best at different frequencies
What is ultrasound?
Sounds made by waves with higher frequencies above 20,000 Hz (20 kHz)
What do sonar equipment do?
They are carried on ships or submarines that find the depth of the sea or detect fish using a loudspeaker that emits a pulse of ultrasound which spreads out through the water and some of it is reflected by the sea bed. A special mic detects the echo and the equipment measures the time between the sound being sent out and the echo returning. The distance is then calculated by speed X time
What is the gel in ultrasound scans for babies used for?
To stop the ultrasound just reflecting from the skin of the mother
What is infrasound?
Sounds with a frequency less than 20 Hz
What are the vibrations caused by earthquakes called?
Seismic waves
How can seismic waves be detected?
By longitudinal P waves and transverse S waves using a seisometer
What can P waves travel through?
Liquids and gases
What can S waves travel through?
Solids
What is the S wave shadow zone?
A large area of Earth on the opposite side to the earthquake where no S waves are detected
Why does the shadow zone of S waves occur?
Because part of the interior of the Earth is liquid, which S waves cannot travel through
