P4 | waves Flashcards
what is sound with frequencies greater than 20,000Hz known as?
ultrasound
ultra = beyond
what is sound with frequencies less than 20Hz known as?
infrasound
infra = below
why does sound travel faster in liquids than in gases?
sound travels faster in liquids because the molecules are more tightly packed
wave speed formula
v = λ x f
what happens to frequency as sound waves travel from a less dense to more dense medium?
stays constant
what happens to wave speed as sound waves travel from a less dense to more dense medium?
increases
what happens to wavelength as sound waves travel from a less dense to more dense medium?
increases
why is it difficult to predict when an earthquake will happen?
movement of tectonic plates/release of energy in earth’s surface is sudden/random and it is difficult to measure when the release of energy will occur/plates will collide
order of earth’s structure (outer most to inner most)
crust (solid)
mantle (semi-solid)
outer core (liquid)
inner core (solid)
properties of p waves
primary waves (arrive first)
can travel through solids and liquids therefore they can pass through all of earth’s layers
longitudinal
shake the ground up and down
properties of s waves
secondary waves (arrive second)
can only travel through solids
transverse
shake the ground side to side
what should you always do to your answer for sonar pulse calculations?
divide by 2 at the end
how do scientists use seismic stations to locate where an earthquake happened?
work out the time between S and P waves to find out the time delay between them
d = s x t to calculate the distance the wave travelled
pick three stations and draw circles with the possible maximum distance
where they overlap is the epicentre (called triangulation)
what is S-P time
time difference between arrival of P waves and S waves
how is UV light used to check bank notes?
UV light absorbed by banknote which emits light into eye
uses of infrasound
- investigating the internal structure of earth
- communication between elephants/dolphins
uses of ultrasound
- foetal scanning
- animal communication
how does sound travel through air?
sound waves travel along vibrations of air particles parallel to the direction of energy transfer as longitudinal waves
how are sound waves detected by an ear?
- sound waves are collected by the outer ear (pinna)
- the waves travel along the ear canal
- the waves reach the eardrum and make it vibrate
- small bones called ossicles amplify the vibrations
- the cochlea turns these into electrical signals
- the auditory nerve takes the signals to the brain
how are ultrasounds used for foetal scanning?
- ultrasound waves pass through the body
- when they reach the boundary between fluid in the womb and the skin of the foetus, some of the wave is reflected back and detected
- the exact timing and distribution of the waves are processed by a computer to produce a video image of the foetus
