Ch12 Wave properties Flashcards
Electromagnetic wave properties
All travel through a vacuum at 3x10^6 km/s
Transverse waves
The oscillations are perpendicular to the direction in which the waves transfer energy
Longitudinal waves
Oscillations of a longitudinal wave are parallel to the direction in which the waves transfer energy
Examples of transverse waves
- Waves on a rope
- Ripples in water
- Electromagnetic waves
- S-waves
Examples of longitudinal waves
- sound waves
2. P-waves
Wave speed
v = frequency x wavelength
Frequency equation
1/ period(T)
Amplitude of a wave
Maximum displacement of a point on a wave from its in disturbed position
Frequency
The amount of waves passing a fixed point per second
Period
The amount of time taken for each wave to pass a fixed point
Period equation
period = 1/ frequency
Speed of sound in air
340m/s at 15degrees
Ears range frequency
20Hz - 20KHz
Ultrasound waves
Sound wave that vibrates above 20KHZ
Non-ionising
How ultrasound machine works
- Transducer transmits and detects sets of ultrasound waves
- Waves are partially reflected back to device at boundaries between different types of mediums(tissues)
- If you know the speed of the wave and how long it takes to be reflected, can work out how far away boundary is (s = 1/2t x v)
- Scans internal structure(e.g organs) and is used to build up image of internal tissue
Uses of ultrasound
- medical imaging( e.g. prenatal scans)
- industrial imaging (e.g crack in supposed solid structure)
- echo sounding(e.g. sea floor)
Seismic waves
Produces by earthquakes
Primary waves
last about 1 minute
Push and pull on Earth’s material
Secondary waves
Slower than primary waves
Shake material that they pass through from side-side
L-waves
slowest
violent movement up-down and forwards-back
only occur in the crust
Shadow zone(liquid outer-core under the mantle)
- P-waves are refracted at boundary between mantle and outer core because speed changes abruptly at boundary
- S-waves can’t travel through liquid outer core because they are transverse
Boundary between crust and mantle
Discovered when found out speed of seismic wave changed at depth of 50km below surface
Core has solid inner part
Weak P-waves detected in shadow zone
Solid inner part refracts P-waves at boundary between outer core and inner core into the shadow zone
