P12 Wave properties Flashcards
what are the categories for waves?
transverse
or
longitudinal
what do waves do?
transfer energy from one place to another
what are transverse waves?
a wave where the oscillations are perpendicular to the direction of energy transfer
what are rarefractions?
regions in a longitudinal wave where particles are spread out
what is a longitudinal wave?
a wave which has oscillations parallel to the direction of energy transfer
what do all longitudinal waves need to travel?
a medium
what travels, the medium or the wave?
the wave
the medium does not travel along the wave
what is the amplitude of a wave?
the maximum displacement of a point on a wave from its undisturbed position
what is the wavelength of a wave?
the distance from a point on one wave to the equivalent point on the adjacent wave
what does lambda mean?
wavelength
what is frequency?
the number of wave passing a point each second
what is the unit of frequency?
the Hertz (Hz)
what is the period of a wave?
the time (in seconds) for one wave to pass a point
what is wave speed?
the speed at which a wave moves through a medium
what is the equation of wave speed?
v = frequency (Hz) x wavelength (m)
how can you investigate the speed of sound waves?
two people stand 500m apart, one is holding cymbals (person A) while the other is holding a timer (person B).
person B starts the timer when they see person A crash the cymbals and stop it when they can hear the sound.
then they divide the distance by the time taken to work out the speed
what are some problems with the method of investigating the speed of sound waves?
every person has a different reaction time - can be reduced with multiple observers with timers
time between seeing and then hearing the cymbals is very short - increase distance between people
what is the easiest way to measure different properties of a water wave?
the ripple tank using a phone so that you can watch it at different speeds or freeze the image
how do you measure the wavelength of water waves in a ripple tank?
freeze the image taken on a phone
measure the distance of 10 waves in total using a ruler
divide the result by 10 to get 1 wavelength
how do you calculate the frequency of water waves in a ripple tank?
use a time and count the number of waves passing a point in 10 seconds.
then divide the result by 10 to get the number of waves passing a point in 1 second
what is another way to work out the wave speed of water waves in a ripple tank?
select a wave and measure the time it takes for it to move the length of the tank.
then divide the distance travelled by the time taken to work out the speed
how do you measure the wavelength of a standing wave?
measure from the wooden bridge to the vbration generator
how do you know the frequency when investigating waves in a solid?
you know the frequency from the signal generator
what can you see from the investigation of wave speed in solids?
the wave speed is not dependent on the frequency or wavelength
it depends on the taughtness of the string and the mass/cm of the sting
what could happen when a wave hits a boundary with a different material?
- it could be transmitted through the material
- the energy of the wave could be absorbed by the material
- it could be reflected off the surface of the material
what is the incident ray?
the ray of light which strikes the surface of the reflective material
what is the normal?
the line drawn perpendicular to the surface of the mirror or other material
what is the angle of incidence?
the angle between the incident ray and the normal
what is the rule of reflection?
the angle of incidence equals the angle of reflection
what is used to investigate reflection and refraction of light rays?
a ray box, lens and slit
in the investigation of reflection and refraction of different materials, what will you find about the angles of reflection and refraction of different materials?
the angles of incidence and reflection are the same for each material investigated
this is because these angles do not depend on the material
the angle of refraction will be different for each material
this is because the angle of refraction is different for different materials
what can sound waves in air do to a solid?
trigger vibrations in a solid
this only works for a limited range of frequencies
what is the frequency range of human hearing?
20 Hz to 20 000 Hz
why can frequencies outside the human frequency range not be heard?
they may not be able to make the human ear drum vibrate
what happens when waves move from one medium to another?
the speed can change
the wavelength also changes
what does not change when a wave changes medium?
the frequency of the wave
this is because the wave would have to be destroyed or created at the boundary for the frequency to change and that is not possible
what does the frequency mean about a sound wave?
the frequency is the pitch of the sound
a high frequency has a high pitch
a low frequency has a low pitch
what does the amplitude mean about a sound wave?
the volume of the sound depends on the amplitude
a small amplitude has a quiet sound
a large amplitude has a loud sound
why can sound waves not pass through a vacuum?
sound waves need a medium to travel as they move by vibrating particles
in a vacuum, there are no particles so the sound wave cannot pass through
what is an echo?
a reflected sound wave
what is ultrasound?
sound waves with a frequency higher than the upper limit of human hearing
what do ultrasound waves do do at boundaries of two different densities?
they partially reflect
what does ultrasound scanning work for?
organs not surrounded by bone
what is the formula for distance when using ultrasound?
s (distance) = v (speed) x t
what is the structure of the earth?
outer crust
solid mantle with some parts that can flow
liquid outer core
solid inner core
when does an earthquake happen?
when there is a sudden movement of the earth’s tectonic plates
what are the properties of P waves?
they are longitudinal
they can pass through liquids and solids
they are faster than S waves
what are the properties of S waves?
they are transverse
they can only travel through solids
why do seismic waves travel in curved paths?
the density changes in the earth
what is the area of the earth where S waves cannot be detected?
the S wave shadow zone
why is there an S wave shadow zone?
S waves cannot pass through liquids (the liquid outer core!)
what causes the P wave shadow zone?
P waves travel faster in solids than they do in liquids
this means the P waves slow down as they enter the outer core and refract
they also refract when they leave the outer core
how did scientists know there was a solid inner core?
faint P waves could be detected in the P wave shadow zones
how can the amount of infrared radiation emitted from different surfaces be measured?
using a leslie’s cube
how can you use a Leslie’s cube to investigate infrared radiation?
fill the cube with hot water
point the infrared detector at the four surfaces and record the amount of infrared radiation
keep the detector at the same distance for each measurement to keep it repeatable
list the amount of infrared radiation the surfaces on a Leslie’s cube emit from most to least?
matt black
shiny black
white
shiny metallic
how do you measure the absorbance of different surfaces of infrared radiation?
use an infrared heater with metal plates on either side
each plate has been painted with different surfaces (e.g. matte black on one and shiny on the other)
attach a drawing pin with vaseline on to each plate and turn on the heater
start timing
record the time it takes for the vaseline to melt and the pin to fall off
what can happen when waves move from one medium to another?
they can change direction when the change speed
what happens when waves slow down?
they bend towards the normal
what happens when waves speed up?
they bend away from the normal
when do waves not change direction through a medium?
when the waves enter or leave the medium at right angles to the surface
what is a wavefront?
an imaginary line which connects the same points on a set of waves
why do waves change direction when they enter another medium?
only part of the wavefronts slow down/speed up, causing them to bend towards or away from the normal
