waves Flashcards
what are the two types of waves?
-transverse
-longitudinal
what is a transverse wave?
a wave for which the oscillations are perpendicular to the direction of energy transfer
what is a longitudinal wave?
a wave for which the oscillations are parallel to the direction of energy transfer
give two examples of transverse waves
-electromagnetic waves
-seismic s-waves
give two examples of longitudinal waves
-sound waves
-seismic p-waves
what are the two parts of a longitudinal wave called?
compressions and rarefactions
what is a wave’s amplitude?
the maximum displacement of a point on a wave from its undisturbed position
what is wavelength?
-the distance from a point on a wave to the same position on the adjacent wave
-most commonly peak to peak or trough to trough
what is the frequency of a wave?
the number of waves that pass a given point each second
what is the unit used for frequency?
hertz, Hz
what is meant by a frequency of 200Hz?
200 waves pass a given point each second
what is wave speed?
the speed at which the wave moves or at which energy is transferred through a medium
what does a wave transfer?
energy
state the equation used to calculate wave speed. give appropriate units
wave speed = frequency x wavelength
speed (m/s), frequency (Hz), wavelength (m)
what word is used to describe when a wave bounces off a surface?
reflection
how do sound waves travel through a solid?
the particles in the solid vibrate and transfer kinetic energy through the material
what is the frequency range of human hearing?
20Hz - 20kHz
(1kHz = 1000Hz)
what are ultrasound waves?
waves which have a frequency higher than the upper limit of human hearing (20kHz)
give an example use for ultrasound waves?
medical or industrial imaging
what natural event causes seismic waves to be produced? what types are produced?
-earthquakes
-they produce both P-waves and S-waves
state a difference between the mediums that P-waves and S-waves can travel through
-P-waves travel through both solids and liquids
-S-waves only travel through solids (not liquids)
what technique is used to detect objects in deep water and measure water depth?
-echo sounding
-high frequency sound waves are emitted, reflected and detected
-time difference between emission and detection, alongside wave speed, are used to calculate distances
what type of spectrum do electromagnetic waves form?
a continuous spectrum
order the types of electromagnetic radiation from lowest to highest frequency
-radio waves
-microwaves
-infrared
-visible light
-ultraviolet
-x-rays
-gamma rays
how do the speeds of EM radiation differ in a vacuum and in air?
electromagnetic waves all travel at the same speed in a vacuum and in air
what property of waves in different mediums causes refraction?
-velocity
-wave speed is slower in denser materials, causing refraction
in which direction (relative to the normal) do waves refract when entering a denser medium?
-they bend towards the normal
-the angle of refraction is less than the angle of incidence
what type of waves can be produced by oscillations in an electrical circuit?
radio waves
how can radio waves create an alternating current in a circuit?
when radio waves are absorbed, they can induce oscillations in a circuit with the same frequency as the waves themselves
where do gamma rays originate from?
they originate from changes in the nuclei of atoms
what health effects can ultraviolet waves cause?
-they can cause the skin to age prematurely
-they can increase the risk of developing skin cancer
what health effects can x-rays and gamma rays cause?
-they are ionising radiation so can cause mutations in genes
-they can lead to increased risk of developing various cancers
give three practical uses for infrared radiation
-electrical heaters
-cooking food
-infrared cameras
give two practical uses for microwave radiation
-satellite communications
-cooking food
give two practical uses for radio waves
-television transmission
-radio transmission
what is a ripple tank?
a shallow glass tank with an oscillating paddle / needle to create waves. it is illuminated from above so the waves can be seen on the surface below the tank
outline the basic steps of observing water waves in a ripple tank
1) set up the ripple tank with a lamp above it and white card/paper below it
2) switch on the motor attached to the wooden rod
3) measure the wavelength of the waves being cast onto the card
4) count the number of waves passing a point in 10 seconds and calculate the frequency
5) calculate the wave speed
approximately how much water should you put into the ripple tank? what would the consequence of too much be?
the water should be poured to a depth of around 5 mm. if there is too much water the rod won’t produce clear waves and they will be less clearly projected onto the card below
how should the wooden rod be set up in the ripple tank?
the wooden rod should be placed into the tank so that it just touches the surface of the water
how should you measure the wavelengths of the waves on the card?
1) adjust the lamp position so that the waves are clearly projected onto the card
2) using a metre rule, measure across as many
waves as you can
3) divide the distance by the number of waves measured across
what units should you measured wavelength be in?
metres, m
(it may be easier to measure in cm, but wavelength must be in m for the wave equation)
why should you measure across more than one wave?
to reduce the uncertainty in the measurement and improve the accuracy of the value
how do you measure the frequency of the waves on the card?
1) count the number of waves passing a chosen point in 10 seconds
2) divide the number by 10, to produce a frequency in Hz
what equation is used to calculate wave speed?
wave speed = frequency x wavelength
when the frequency is in hertz and the wavelength is in metres, what is the unit for wave speed?
m/s
metres per second
outline the basic steps of observing waves in a solid
1) attach a piece of string to a vibration generator at one end and to a mass hanger suspended over a pulley at the other
2) place the wooden bridge under the string before it reaches the pulley
3) start the generator and alter the tension and bridge until it looks like the wave isn’t moving
4) measure the wavelength, and record the frequency
5) calculate wave speed
how do you measure the wavelength in a solid?
1) using a metre ruler, measure across as many loops as you can
2) each loop is a half wavelength
3) divide the distance by the number of loops and multiply by two to get the wavelength
what value is used for the frequency?
the value should be taken from the frequency generator settings
outline the basic steps of the radiation and absorption practical
1) place a leslie cube on to a heatproof mat and fill with hot water
2) use the infrared detector to measure the amount of radiation that is emitted from each side
3) draw a suitable chart to compare the results for each surface
what is a leslie cube?
a cube with different textured surfaces used to demonstrate the differing radiation emitted. typically it has a matt white, a shiny silver / gold, a matt black and a shiny black side
why is a heatproof mat used in the radiation and absorption practical?
boiling water is poured into the cube meaning the base can get hot and so a mat is used to protect the desk
what type of data is collected from the radiation and absorption experiment?
the four different surfaces being measured produces categorical data
give an example of a chart that may be used to display the data from the radiation and absorption practical
a bar chart with radiation intensity on the y-axis and the four surfaces on the x-axis
which surface would you expect to emit the most radiation?
the matt black surface since good absorbers of radiation are also good emitters. matt black surfaces are good emitters and poor reflectors
which surfaces would you expect to emit the least radiation?
the shiny surfaces, as they are good reflectors and poor emitters
what type of radiation is being emitted?
infrared radiation, which is part of the electromagnetic spectrum
what piece of apparatus is useful when filling the cube and why?
a funnel since the opening is very small and it will reduce the likelihood of spillages
what safety precaution should be taken when using a leslie cube?
avoid handling it with bare hands when filled with boiling water since the cube will be very hot
