Science- Physics - Waves - P6 Flashcards
what is a wave ?
an oscillation that transfers energy without transferring any matter, making the particles of the substance that it is travelling through oscillate
what is an oscillation ?
a vibration
what are the 2 types of waves ?
transverse
longitudinal
what are transverse waves ?
where the oscillations are perpendicular ( at 90 degrees) to the direction of energy transfer of the wave
where do waves transfer energy ?
in the same direction they travel
give an example of a transverse wave ?
light
other electromagnetic waves
what are longitudinal waves ?
waves with oscillations along the same line they travel with areas of compression and rarefaction, the oscillations are parallel to the direction of energy transfer of the wave
what is rarefaction ?
where the particles are spread out
what is compression ?
where the particles are bunched together
give an example of longitudinal waves ?
sound waves
a spring when you push the end
do waves transfer matter ?
no
what happens in waves ?
they travel through a medium and the particles of the medium oscillate and transfer energy between each other but overall the particles stay in the same place, only energy is transferred
what are crests and troughs ?
points of maximum positive and maximum negative displacement from the particles rest position
what is the amplitude ?
the maximum displacement of a point on the wave from its undisturbed position - the distance from the undisturbed position to a crest or trough
what is a wavelength ?
the distance between the same point on 2 adjacent waves
what is the frequency ?
the number of complete waves passing a certain point per second
what is frequency measured in ?
hertz
what is the period of a wave ?
the amount of time it takes for a full cycle of the wave to be completed - the length of time between 1 crest passing a point and the next crest passing the same point
what is wave speed ?
the speed at which energy is being transferred
how do you measure the speed of sound in air ?
find the frequency and the wavelength of a sound wave
how can you generate a sound wave ?
- using a specific frequency
- attach a signal generator to a speaker
- the sound wave can then be detected by microphones
- these convert it to a trace on an oscilloscope
describe the method of how to measure the speed of sound in air ?
- set equipment up with both microphones next to the speaker, the detected wave at each microphone can be seen as a separate wave on the oscilloscope
- slowly move the microphone away from the speaker, its wave will shift sideways on the oscilloscope keep moving until the 2 waves on the oscilloscope are aligned again, at this point the microphones will be exactly 1 wavelength apart so measure the distance between them
why are water ripples useful for investigating wave properties ?
they are visible
what do you use to produce waves ?
a signal generator
what equipment do you need when measuring the speed of water ripples ?
a ripple tank which is made of glass
why do you use a ripple tank ?
to show the properties of waves as the glass bottom of the tank means light can be shone onto the tank from above to project the wave pattern onto a screen below
how do you carry out the measuring the speed of water ripples experiment ?
- set up equipment
- fill ripple tank with water of a depth of 5mm
connect dipper to a signal generator and set it off at a known frequency - dim lights and turn on lamp to see wave pattern
- the distance between each shadow line = 1 wavelength
- measure the distance of 10 ripple waves and divide by 10 to get wavelength using a ruler
what do you need to observe waves on a string ?
- taut string
- vibration transducer
what is a vibration transducer ?
something that will convert an electrical signal from a signal generator into vibrations
how can you ensure the string is taut ?
by connecting one end of it to a vibration transducer and passing it over a pulley with masses hanging from the other end
how do you carry out the observing a wave on a string practical ?
set up equipment and turn on signal generator and vibration transducer
- string will start to vibrate
- adjust frequency of signal generator until there’s a clear eave on the string
- measure the wavelength of the waves created
best way to do this is measure the length of 4/5 waves and divide by 4/5 to get the average half- wavelength then double
-
what 3 things can happen when waves arrive at a boundary between 2 different materials ?
- absorption
- reflection
- transmission
what is absorption ?
- waves may be absorbed by the material
- the wave is trying to cross into this transfers energy into the materials energy stores
what is reflection ?
the waves may bounce back
what is transmission ?
waves may be transmitted which means they carry on travelling through the material however they often undergo refraction
what is refraction ?
when the wave reaches a boundary at an angle and changes direction
what is a ray ?
a straight line showing the path a wave travels along
how do you draw a ray diagram ?
- draw the boundary between the 2 materials and then add inthe normal
- draw an incoming incident ray that meets the normal at the boundary, the angle which is between the ray and the normal is the angle of incidence
- draw the refracted ray on the other side of the boundary the angle that the refracted makes with the normal is called the angle of refraction
- the angle of refraction could be smaller than the angle of incidence or bigger
what is the angle of incidence ?
the angle between the ray and the normal
what is the angle of refraction ?
the angle that the refracted ray makes with the normal
when is the angle of incidence greater than the angle of refraction ?
when light moves from air into a glass block
when is the angle of incidence smaller than the angle of refraction ?
when light moves from glass into the air
if the ray passes along the normal and hits the boundary at 90 degrees what happen ?
it will pass through without changing direction, the angles of incidence and refraction will be at 0 degrees
why does refraction occur ?
waves travel faster in some materials than others so the speed of a wave can change as it crosses a boundary
when a wave refracts what happens to it speed and frequency and wavelength ?
its speed changes but its frequency stays the same
wavelength increases/decreases with speed
what is the optical density of a material ?
how quickly light travels through it, the higher the optic density, the slower the light travels
what are wavefronts ?
imaginary lines drawn through certain points on waves, e.g through each crest and are perpendicular to the direction where the wave is moving
when are wavefronts closer together ?
in more optically dense materials, showing the decrease in wavelength
why are wavefront diagrams useful ?
to explain why refraction happens
how do waves refract ?
- when a wave crosses a boundary into a new substance at an angle to the normal one end of it enters the new material before the rest of the wave
- this means that end of the wave enters the enw material before the rest of the wave and changes speed before the rest of the wave causing the wave to change direction and refract
what does which way the wave bends depend on ?
- whether it moves faster or slower in the new medium
if the wave slows down at a boundary, what happens ?
it bends towards the normal
if a wave speeds up at a boundary what happens ?
it bends away from the normal
as well as being refracted, what could also happen to a wave between 2 materials ?
it could be reflected
how do you show reflection in a ray diagram ?
draw the incoming ray and the reflect ray as well as the normal
what is the law of reflection ?
angle f incidence = angle of reflection
what is the angle of reflection ?
the angle between the reflected wave and the normal
what is specular reflection ?
when parallel waves are reflected in a single direction by a smooth surface
give an example of specular reflection ?
when light is reflected by a mirror
what is diffuse reflection ?
when parallel waves are reflected by a rough surface and the reflected waves are scattered in lots of directions
in diffuse reflection, what is the angle of incidence and why ?
equal for the angle of reflection for each ray, however the tiny bumps on the surface mean the normal ray is different so the angle of incidence is different for each ray
when light is reflected by a rough surface what happens ?
the surface appears matt and unclear
what conditions are experiments of light best in ?
a dim room
why are ray boxes or lasers used ?
to produce thin rays of light so you can see the middle of the ray when tracing it and measuring angles from it
how do you carry out the investigating refraction practical ?
- place a transparent rectangular block on a piece of paper and trace around it
- use a ray box to shine a ray of light at the middle of 1 side of the block
- trace the incident ray on the paper and do the same for the light ray that emerges on the other side of the block
- remove the block and with straight lines join up the lines of the incident and emerging ray this shows the path of the refracted ray
- draw the normal point where the ray entered the block
- use a protractor to measure the angle between the incident ray and the normal and the angle between the refracted ray and the normal
- repeat this using blocks from different materials keeping the incidence angle the same throughout
why do we carry out the investigating refraction practical
to see how the boundaries of different substances refract light by different amounts
why do we carry out the investigating reflection practical ?
to see how surfaces reflect light in different ways depending on how smooth they are
how do you carry out the investigating reflection practical ?
- take a piece of paper and draw a straight line across it
- place straight edged object on the paper so it lines up with this line
- shine a ray of light at the objects surface and trace the incoming and reflected light beams
- add in a normal line which meets the surface at the point of incidence
- draw and label the incident and reflected rays
- use a protractor to measure the angle of incidence and the angle of reflection and record these values in a table
- also measure the length of the reflected ray and how bright it is
- repeat with a range of objects
what should the results of the investigating reflection practical be ?
smooth surface like mirrors give clear reflections whereas rough surfaces cause diffuse reflection where the reflected beams are wider and dimmer
how do lenses form images ?
lenses form images by refracting light and changing its direction
what are the 2 type of lenses ?
convex (converging)
concave ( diverging)
what is a convex lens ?
a lens which bulges outwards, it causes rays of light which are parallel to the axis of the lens to converge (come together) at the principle focus
what is the axis of the lens ?
a line passing through the middle of the lens, perpendicular to the lens
where is the principle focus of a convex lens ?
where rays hitting the lens parallel to the axis all meet
what is the focal length ?
the distance from the center of the lens to the principle focus
where is there a principle focus ?
on each side of the lens
where will rays from convex lenses parallel to the axis focus ?
on the principle focus on the far side of the lens in relation to where the rays are coming from
what are the 3 main rules for convex lenses ?
- an incident ray travelling parallel to the axis refracts through the lens and passes through the principle focus on the other side
- an incident ray passing through the centre of the lens carries on in the same direction
- an incident ray passing through the principal focus before meeting the lens refracts through the lens and travels parallel to the axis
what is a concave lens ?
a lens which caves inwards , it causes parallel rays to diverge (spread out)
what is the principle focus of a concave lens ?
it is the point where rays hitting the lens parallel to the axis appear to all come from
what are the 3 rules for concave lenses ?
- an incident ray travelling parallel to the axis refracts through the lens and travels in line with the near side principle focus
- an incident ray passing through the centre of the lens carries on in the same direction
- an incident ray passing through the lens towards the far side principal focus refracts through the lens and travels parallel to the axis
what are the 2 types of images ?
real
virtual
what is the type of image produced dependent on ?
whether the 2 light rays coming from the same point on an object will eventually meet
how is a real image formed ?
when the light rays from a point on an object come together to form an image
the light rays actually pass through the same point
what can a real image be captured on ?
a screen - like the image formed on an eyes retina
how is a virtual image formed ?
when the light rays from a point on an object are diverging after they have left the lens so the light from the point on the object appears to be coming from a completely different place
in virtual images do light rays pass through the point >
?
no, they just appear to
give an example of a virtual image ?
a mirror
where can you get a virtual image ?
when looking at an object through a magnifying lens as the virtual image looks bigger than the object actually is
what do you need to say when describing an image ?
how big it is compared to the object
whether its upright or inverted, relative to the object
whether its real or virtual
what is a ray diagram ?
a diagram showing the paths taken by light rays through a lens
what do ray diagrams help with ?
work out what an image formed by the lens will be like
how do you draw a ray diagram for convex lenses ?
- draw a ray form the top of the object that passes straight through the centre of the len without changing direction at all
- draw a second ray from the top of the object that travels parallel to the axis, the ray should refract at the lens so it passes through the principal focus of the lens, the rays may or may not meet
- repeat to check
- draw the image, the point where the 2 rays from the top of the object meet is where the top of the image is formed. The point where 2 rays from the bottom of the object meet is where the bottom of the image is formed
when the bottom of the object is on the axis, what is also on the axis ?
the bottom of the image
what does the type of image formed by a convex lens depend on ?
where the object is placed in relation to the principal focus
what will an object beyond 2F produce ?
a real, inverted image that is smaller than the object, it will sit between F and 2F on the far side of the lens
what will an object placed at 2F produce ?
a real, inverted image that is the same size of the object, it will sit at 2F on the far side of the lens
what will an object placed between F and 2F produce ?
a real, inverted image that is bigger than the object, it will sit beyond 2F on the far side of the lens
what will an object placed between the lens and F produce ?
a virtual image that is the right way up but bigger than the object and the same side of the lens as the object
how do you draw ray diagrams for concave lenses ?
- draw a ray from the top of the object that passes straight through the centre of the lens without changing direction at all
- draw a 2nd ray from the top of the object that travels parallel to the axis, the ray should refract at the lens so that it appears to have to come from the near side principal focus , draw a virtual ray from that principal focus to where that ray meets the lens
- repeat the process
- draw the image , where the real and virtual rays from the top of the object meet is where the top of the image is formed, where the real and virtual rays from the bottom of the object meet is where the bottom of the image is formed
what does a concave lens always produce ?
a virtual image, the right way up, smaller than the object and on the same side of the lens as the object
convex lenses converge light wheras concave lenses …
diverge light
where do rays parallel to the axis converge onto on a convex lens ?
principal focus, but diverge so that they appear to have come from the principal focus of a concave lens
what can convex lenses produce ?
real and virtual images
what can concave lenses produce ?
virtual images
what type of lenses do magnifying glasses use ?
convex lenses
how do magnifying glasses work ?
by creating a virtual, upright image that is larger than the object and is on the same side of the lens as the object for this to happen the object being magnified must be closer to the lens than the focal length
in magnifying glasses, why don’t the light rays come from the place where the image appears to be ?
as it is a virtual image
why doesn’t magnification have a ratio ?
it is a ratio so as long as the units are the same for both you can measure heights in whatever lengths you like
what are sound waves ?
longitudinal waves of vibrating particles caused by vibrating objects