Waves Flashcards
properties of longitudinal waves
- the oscillations are parallel to the direction of energy transfer
- all longitudinal waves require a medium to travel in
examples of longitudinal waves
sound waves in air
- ultrasound
- P waves
properties of transverse waves
- the oscillations are perpendicular to the direction of energy transfer
- not all transverse waves require a medium to travel in
examples of transverse waves
- electromagnetic waves
- ripples and waves in water
- a wave on a string
- S waves
what is the amplitude of a wave
the maximum displacement of a point on the wave from its undisturbed position
what is the wavelength
the distance between the same point on two adjacent waves
what is the frequency
the number of complete waves passing a certain point per second
period equation
1/frequency
- measured in seconds
wavespeed calculation
frequency x wavelength
all waves transfer….
energy but not matter
what can waves do at boundaries
- Be absorbed
- Be transmitted
- Be reflected
what is the law of reflection
angle of incidence = angle of reflection
what types of waves are EM waves
transverse
properties of EM waves
- all travel at the same velocity through a vacuum or air (300 million metres per second)
- transfer energy as radiation from the source of the waves to an absorber
- can travel through a vacuum such as in space
- transverse waves
what are EM waves
transverse waves that transfer energy
from the source of the waves to an absorber
order of EM waves going from shortest wavelength/ frequency to longest
radio, microwave, infrared, visible light (red to violet), ultraviolet, Xrays and gamma rays
uses of radiowaves
- used for communication such as television and radio.
- terrestrial tv
properties of radiowaves that make it suitable for its uses
- transmitted easily through air
- do not cause damage if absorbed by the human body
- they can be reflected to change their direction
what happens when radiowaves are absorbed
When radio waves are absorbed they may create an
alternating current with the same frequency as the radio wave itself,
so radio waves can themselves induce oscillations in an electrical
circuit
microwaves uses
Microwaves are used for cooking food and for satellite communications.
properties of microwaves that make it suitable for its uses
- pass easily through the atmosphere without being reflected or refracted
- so they can pass between stations on Earth and satellites in orbit
how do microwaves heat food
High frequency microwaves have frequencies which are easily absorbed by molecules in food. The internal energy of the molecules increases when they absorb microwaves, which causes heating
infared uses
electrical heaters, cookers for cooking food, and by infrared cameras which detect people in the dark
how does infared cause heating
- infrared light has frequencies which are absorbed by some chemical bonds
- the internal energy of the bonds increases when they absorb infrared light, which causes heating
visible light use
fibre optic communications
Ultraviolet uses
– energy efficient lamps, sun tanning
what do waves do
they transfer energy from one place to another, but do not transfer any matter
what can happen to a wave at a boundary
- can be reflected, absorbed or transmitted
how to find out the wavelength on a longitudinal wave
measure from one compression to another, or from one rarefaction to another
what is a period
the time for one wave to pass a point
what is the wavespeed
the speed at which the wave moves through the medium
how to measure sound waves in air
- Get one person to hold cymbals and get the other to hold a timer
- Get the person to start timing when the other person clashes the cymbals together
- Stop timing when she hears the sound of the cymbals
- calculate the speed of the sound waves by dividing distance travelled by the time taken
problems with measuring sound waves in air experiment and how they can be fixed
- everyone has a different reaction time, can be reduced by having a large number of observers with timers, take all of their results and discard any anomalies
- the time between seeing the cymbals clash and hearing the sound is very short, making it difficult to press the timer at the correct time, can b fixed by increasing the distance between the two people as the longer the distance, the longer the time
what happens when sound waves move through the air
the air particles vibrate from side to side, and these vibrations can pass through one medium to another
how does a microphone work in terms of sound waves
- when sound waves hit the paper cone, it vibrates
- the microphone converts these vibrations to electrical signals
how do sound waves in the ear work
- sound waves are funnelled into the ear where they hit the eardrum (the eardrum is a thin membrane)
- the sound waves cause the eardrum and other inner parts of the ear to vibrate and this causes the sensation of sound
what is the frequency range of human hearing
20HZ to 20,000HZ
why do sound waves travel faster in solids
because the particles in solids are much closer together, meaning vibrations can pass more easily between them
what happens to the wavelength as the wavespeed changes from one medium to another
it changes also
why doesnt the frequency change when a wave changes medium
because waves would have to be destroyed or created at a boundary, and this isnt possible
how can we view the features of sound waves
by connecting a microphone to a cathode ray oscilloscope
problems with cathode ray oscilloscope
they represent sound waves as if they were transverse waves
why do sound waves require a medium to travel through
because sound waves move by particles vibrating, they cant pass through a vacuum as there are no particles
what is a reflected sound wave
an echo
what is ultrasound
sound waves with a frequency higher than the upper limit of human hearing
what do ultrasound do at a boundary
it partially reflects at the boundaries between two different densities
uses of ultrasound
can produce images of internal organs such as a kidney and heart, or any organ that isnt surrounded by bone
- can produce images of foetus
- used in industrial imaging
why is ultrasound safer than x rays
- doesnt cause mutations
- doesnt increase risk of cancer
what equation would we use to determine distance using ultrasound
s (distance) = v (speed) x t (time)
what is the speed of ultrasound in water
1600 m/s
properties of the earths crust
thin, max depth 50km
why do earthquakes happen
because of sudden movements between tectonic plates and the earths crust
how can scientists study the internal structures
- earthquakes cause seismic waves which carry energy away from the earthquake
- these seismic waves then pass through the earth and they can be detected by seismometers in different countries
properties of P waves
- longitudinal
- can pass through solids and liquids
- travel faster than s waves
properties of S waves
- transverse waves
- can only travel through solids
why do seismic waves travel in curved paths
because of density changes in the earth
what is the S wave shadow zone
the parts of the earth where no S waves can be detected
why is the S wave shadow zone so big and what does it tell us
because S waves cant travel though liquids, so this tells scientists that the Earth must contain a liquid core
why are there P wave shadow zones
- because P waves travel faster in solids than in liquids, meaning that P waves slow down as they enter the liquid outer core, causing them to refract (change direction)
what do faint p waves tell us
the inner core is solid
colours of light going from low to high frequency
red,orange,yellow,green,blue,indigo,violet
acronym to remember em spectrum
raw meat is very unsanitary except giraffe
when do waves refract
when they change medium
what happens when electromagnetic waves are generated or absorbed
- changes take place in atoms or in the nuclei of atoms
- eg electrons can change energy levels
what happens when an atom emits gamma radiation
the nucleus has less energy than it had at the start
risks of UV waves
- increase risk of skin cancer
- cause skin to age prematurely
risks of X rays and gamma rays
- ionising radiation
- can cause the mutations of genes and increase the risk of cancer
what dies the damage caused by radiation depend on
the type of radiation and the dose
how are radiowaves produced
- produced when electrons oscillate in electrical circuits
- these radiowaves can be absorbed
- when this happens, they now cause electrons in the circuit to oscillate
- This can create an alternating current with the same frequency as the radio waves
properties of visible light that make it suitable for its uses
- short wavelength to carry a great deal of info
properties of UV that make it suitable for its uses
shorter wavelength than light, can carry more energy than light
x rays and gamma rays uses
used for medical imaging
- x rays used to detect broken bones
- gamma used to detect cancers
- can be used in medical treatment
properties of x and gamma rays that make them suitable for their uses
they can pass easily through body tissues
- x rays are absorbed by bone
why does sound travel faster in solids
because sound travels via air particles vibrating and colliding, and because the particles in solids are close together and connected by bonds
what are rarefactions
regions where the air particles are far apart
how do longitudinal waves work
the compressions move from side to side and energy is transferred
no particles are transported along the wave
instead they move backwards and forwards between compressions as the wave in transmitted through a medium
how are radiowaves produced
- by oscillations in electrical circuits
- when radiowaves are absorbed by a conductor, they create an alternating current, and this current has the same frequency as the radiowaves
- information is coded in the wave before transmissions, which can then be decoded when the wave is received
what are uv light, x rays and gamma rays all examples of
ionising radiation
what is radiation dose
a measure of the risk of harm caused by exposing the body to ionising radiation
examples of background radiation
- radioactive rocks in the earths crust
- cosmic rays from space
- man made sources such as nuclear weapon fallouts and nuclear accidents
compressions are what
regions where particles are close together
what is a period
the time take for one wave to pass a point
What happens when we heat atoms?
we cause electrons from one energy level to a higher one
What happens when an electron returns to its original energy level
It generates an electromagnetic wave
