Chapter 12 - Wave Properties Flashcards
What is a wave?
A wave is a transfer of energy from one point to another
What are the 2 types of wave?
not transverse and longitudinal
Mechanical waves
Electromagnetic waves
What is a mechanical wave?
Waves that vibrate through a medium (a substance)
What is an electromagnetic wave?
Waves which can travel through a vacuum (no medium needed)
Give an example of a mechanic and an electromagnetic wave
Mechanic - Sound
Electromagnetic - Light
What is a transverse wave?
The oscillations of a transverse wave are perpendicular to the direction in which the waves transfer energy
What is a longitudinal wave?
The oscillations of a longitudinal wave are parallel to the direction in which the waves transfer energy
‘from its undisturbed position’
What is the amplitude?
The maximum displacement of a point on the wave from its undisturbed position
What is the wavelength?
The distance from a point on the wave to the equivalent point on the adjacent wave
The bigger the amplitude…
the more energy the waves carry
What is frequency?
Frequency is the number of waves passing a fixed point every second
What is the equation linking frequency and time period?
Period (s) = 1/frequency (Hz)
What is the equation linking wave speed, frequency and wavelength?
Wave speed (m/s) = frequency (Hz) x wavelength (m)
The angle of incidence is…
equal to the angle of reflection
What can happen to a light wave when it reaches a boundary between 2 materials?
3 things can happen
Light can be:
- Reflected
- Transmitted (this includes being refracted)
- Absorbed
The human ear can hear between _______________ and _______________
20 Hz and 20kHz
What is ultrasound used for?
3 examples
- Pre-natal scanning (pregnancy)
- Cleaning jewellery
- Breaking down kidney stones
What happens when ultrasound waves are sent to scan organs with an ultrasound transducer?
-The transducer emits a signal
-After a short time it receives a signal back
-This is caused by the ultrasound reflecting off the front of the organ
If a signal from ultrasound is received after a longer time, what does that tell you about the object it reflected off?
It is further away, as the ultrasound has travelled further before being reflected
What is the equation linking speed, distance and time?
Speed = Distance/Time
What are disadvantages of X-rays?
-Ionising radiation (removal of electrons from atoms) could occur which may lead in some cases to mutations and cancers
-X-rays are not reflected at boundaries between different tissues, so are less good at scanning soft tissue and organs
Why do we use ultrasound rather than X-rays for prenatal scanning?
-Ionising radiation is particularly dangerous to a developing foetus
-Any mutations could duplicate during growth and lead to more serious complications than in fully grown adults
What are sound waves?
Sound waves are vibrations that travel through a medium
Why can’t sound travel through a vacuum?
-Sound needs particles to travel
-A vacuum has no particles to vibrate, so sound can’t travel through it
What is it called when a sound reflects off of a surface?
-An echo
-Echoes are better off flat surfaces
What happens to the amplitude if the sound is quieter?
The amplitude is smaller
What happens to the wavelength if the sound is higher pitch?
The wavelength decreases (waves are closer together)
How do you hear sound?
-The ear can detect sound waves
-Sound waves make the ear drum vibrate
-They travel through the solid at this frequency
-Signals are sent to the brain
-The conversion to the solid has a limited frequency range
-For humans this is 20Hz to 20kHz
Seismic waves are produced in an ______
earthquake
Where does the earthquake spread out from?
The epicentre
What is the epicentre?
-It is the nearest point on the surface to where the earthquake originates
-The actual origin is called the focus
What are the 2 types of wave caused by earthquakes (and their types)?
-> P-waves (longitudinal)
-> S-waves (transverse)
Where are P-waves capable of passing through?
Mantle and the outer core
Where are S-waves capable of passing through?
The crust and the mantle, not the outer core
What happens as the P-waves reach the boundaries between the mantle and the outer core?
-> P-waves refract due to different densities (change speed = change direction)
