P6 - waves Flashcards
what is transferred in a wave?
Energy
how are waves transferred through a medium?
the particles of the medium oscillate and transfer energy between each other
do waves transfer particles?
no
what is the amplitude of a wave?
the maximum displacement of a point on the wave from its undisturbed position
what is wavelength?
the distance between the same point on two adjacent waves
what is frequency?
the number of complete waves passing a certain point per second
what is frequency measured in?
hertz
what is 1 Hz
one wave per second
what is the formula to find the period of the wave from the frequency?
T = 1/f
what is the period of a wave?
the amount of time it takes for a full cycle of the wave
what are the two types of wave?
transverse and longitudinal
are there any waves that aren’t either transverse or longitudinal?
no
what are transverse waves?
waves where the oscillations (vibrations) are perpendicular to the direction of energy transfer
are most waves longitudinal or transverse?
transverse
what are three examples of transverse waves?
- all electromagnetic waves (e.g. light)
- ripples and waves in water
- a wave on a string
what are longitudinal waves?
waves where the oscillations are parallel to the direction of energy transfer
what is an example of a longitudinal wave?
sound waves
what is the equation for wave speed?
wave speed = frequency x wavelength
what is wave speed?
the speed at which energy is being transferred (or the speed the wave is moving at)
what can you use to measure the speed of sound?
an oscilloscope
how can you use an oscilloscope to measure the speed of sound?
by attaching a signal generator to a speaker you can generate sounds with a specific frequency. you can use two microphones and an oscilloscope to find the wavelength of the sound waves generated
what are the 5 steps of using an oscilloscope to measure the speed of sound?
- set up the oscilloscope so the detected waves at each microphone are shown as separate waves
- start with both microphones next to the speaker, then slowly move one away until the two waves are aligned on the display, but have moved exactly 1 wavelength apart
- measure the distance between the microphones to find one wavelength
- you can then use the formula wavespeed = frequency x wavelength to find the speed of the sound waves passing through the air - the frequency is whatever you set the signal generator to (around 1 kHz is sensible)
- the speed of sound in air is around 330m/s, so check your results roughly agree with this
what piece of equipment do you need to measure the speed of water ripples?
a ripple tank
what are the 6 steps to measuring the speed of water ripples using a ripple tank
- using a signal generator attached to the dipper of a ripple tank you can create waver waves at a set frequency
- dim the lights in the lab and turn on the lamp. you should see the wave crests as shadows on the screen below the tank
- the distance between each shadow line is equal to one wavelength. measure the distance between shadow lines that are 10 wavelengths apart, and then divide this distance by 10 to find the average wavelength
- this is a good method for measuring the wavelength of moving waves of small wavelengths
- use the formula wave speed = frequency x wave length to calculate the speed of the waves
- this set-up is suitable for investigating waves, because it allows you to measure the wavelength without disturbing the waves
describe the set-up of a ripple tank
a signal generator creates small waves in a shallow tank of waver. there is a lamp above this tank, shining through the water onto the white screen below, causing the crests of the waves to show up as shadows. there is a ruler on the white screen to measure the length of the waves
what set-up do you need when measuring the speed of waves on a string?
a string stretched in the air over the end of a bench, attached to a vibration transducer on one side, and going over a pulley and off the end of the bench on the other side. the vibration transducer is attached to a signal generator, and the end of the string going off the bench is pulled down by weights.
what are the 5 steps to finding the speed of a wave on a string?
- set up the equipment right, then turn on the signal generator and vibration transducer. the string will start to vibrate
- adjust the frequency of the signal generator until there’s a clear wave on the string.
- you need to measure the wavelength of these waves. the best way to do this accurately is to measure the lengths of as many half-wavelengths as you can in one go, then divide to get the mean half-wavelength. you can double this mean to get a full wavelength
- the frequency of the wave is whatever the signal generator’s set to
- you can find the speed of the wave using wave speed = frequency x wavelength
what will the frequency you need to get a clear wave on the string depend on?
the length of the string between the pulley and the transducer, and the masses you’ve used
what waves can be absorbed, transmitted or reflected?
all waves
what are the three things that can happen when a wave meets a boundary between two materials?
- the wave is absorbed by the second material
- the wave is transmitted through the second material
- the wave is reflected
what happens when a wave is absorbed?
the wave transfers energy to the material’s energy stores. Often, the energy is transferred to a thermal energy store, which leads to heating (this is how a microwave works)
what happens when a wave is transmitted through a material?
the wave carries on travelling through the new material. this often leads to refraction and can be used in communications as well as in the lenses of glasses and cameras
what happens when a wave is reflected?
where they incoming ray is neither absorbed nor transmitted, but instead is ‘sent back’ away from the second material. this is how echoes are created
what determines what actually happens when a wave meets a boundary between two materials?
the wavelength of the wave and the properties of the materials involved+
are electromagnetic (EM) waves transverse or longitudinal?
transverse
what do EM waves do?
transfer energy from a source to an absorber
how does a camp fire transfer energy to its surroundings?
it emits infrared radiation. these infrared waves are absorbed by objects and transfer energy to the object’s thermal energy store, causing the object to warm up
how are radio waves used in radios?
radio waves transfer energy to the kinetic energy stores of electrons in radio receivers, which generates an electric current
do EM waves travel at the same speed through air and a vacuum?
yes
what speed do ALL EM waves travel at?
300,000,000 (3 x 10^8) m/s
do EM waves travel at different speeds in different materials?
yes - this can lead to refraction
How much do EM waves vary in wavelength?
from around 10^-15m to more than 10^4m
how are EM waves grouped?
based on their wavelength and frequency
how many basic types of EM waves are there?
7
what type of spectrum do the different groups of EM waves merge to form?
a continuous spectrum
how much of the EM spectrum can our eyes detect?
only the small section of visible light
what are the 7 types of EM wave in order of longest wavelength to shortest wavelength?
- Radio waves
- microwaves
- infrared
- visible light
- ultra-violet
- X-rays
- Gamma rays
do microwaves have a high or low frequency?
low
do infra-red waves have a high or low frequency?
low
do X-rays have a high or low frequency?
high