Topic 6 - Waves Flashcards
What do
waves do?
they transfer energy from one place to another without transferring any matter
Define
amplitude.
the maximum displacement of a point on the wave from its undisturbed position
Define
wavelength.
the distance between the same point on two adjacent waves
Define
frequency.
the number of complete waves passing a certain point per second
this is measured in Hz, 1Hz is 1 wave per second
What is the
crest
of a wave?
the maximum positive displacement of a point on the wave from its undisturbed position
What is the
trough
of a wave?
the maximum negative displacement of a point on the wave from its undisturbed position
What is the
period
of a wave?
the time it takes for a full cycle of the wave
What equation allows you to calculate the
period
of a wave?
period = 1 / frequency
T = 1/f
T: s
f: Hz
What are the
two different types of waves?
transverse and longitudinal
What is the relationship between oscillations and direction in a
transverse wave?
the oscillations are perpendicular to the direction of energy transfer
What is the relationship between oscillations and direction in a
longitudinal wave?
the oscillations are parallel to the direction of energy transfer
What are some examples of
transverse waves?
(3)
- all electromagnetic waves (e.g. light)
- ripples and waves in water
- a wave on a string
(most waves are transverse)
What are some examples of
longitudinal waves?
(2)
- sound waves in air, ultrasound
- shock waves (e.g. some seismic waves)
What is
wave speed?
the speed at which energy is being transferred
(the speed the wave is moving at)
What wave equation links
frequency, speed and wavelength?
wave speed = frequency x wavelength
v = fλ
v: m/s
f: Hz
λ: m
Describe how you would use an
oscilloscope to measure the speed of sound.
(6 steps)
- Attach a signal generator to a speaker (so that you can generate sounds with a specific frequency).
- Set up the oscilloscope so the detected waves at each microphone are shown as separate waves.
- Start with both microphones next to the speaker.
- Slowly move on away until the two waves are aligned on the display (but have moved exactly one wavelength apart.
- Measure the distance between the microphones to find one wavelength.
- You can then use the wave formula to find the speed of the sound wabes passing through the air.
(the frequency is whatever you set the signal generator to)
around 1kHz is sensible
What is the
speed of sound in air?
around 330m/s
Describe how you would
measure the speed of water ripples usig a lamp.
(5 steps)
- Attach a signal generator to the dipper of a ripple tank in order to create water waves at a set frequency.
- Use a lamp to see wave crests on a screen below the tank. Make sure the size of the waves’ shadows are the same size as the waves.
- The distance between each shadow line is equal to one wavelength.
- Measure the distance between shadow lines that are 10 wavelengths apar, then divide this by 10 to find the average wavelength.
- Use the wave equation to calculate the speed of the waves.
If you’re struggling to measure the distance, you could take a photo of the shadows and ruler, and find the wavelength from the photo instead.
Describe how you would calculate the
speed of waves on string.
(7 steps)
- On one end of a bench, attach a signal generator to a vibration transducer.
- On the other end, attach a pulley.
- Attach a piece of string to the vibration transducer, over the pulley and attach some masses on the end.
- 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.
- You can find the speed of the wave using the wave equation.
(the frequency of the wave is whatever the signal generator is set to)
The best way to accurately measure the wavelength is to measure the lengths of four or five half-wavelengths in one go, then divide to get the mean half-wavelength. (You can then double this mean to get a full wavelength.)
What are the 3 things that can happen when
waves arrive at a boundary between two different materials?
- The waves are absorbed by the material the wave is trying to cross into (transferring energy to the material’s energy stores)
- The waves are transmitted (they carry on travelling through the new material
- The waves are reflected
What is the
rule for all reflected waves?
(to do with angles)
angle of incidence = angle of reflection
i = r
What is the
point of incidence?
the point where the wave hits the boundary
What is the
normal?
the imaginary line that’s perpendicular to the surface at the point of incidence
this is usually shown as a dotted line
What is the
angle of incidence?
the angle between the incoming wave and the normal
What is the
angle of reflection?
the angle between the reflected wave and the normal
What is
specular reflection?
and give an example.
when a wave is reflected in a single direction by a smooth surface
e.g. when light is reflected by a mirror
(resulting in a nice, clear reflection)
What is
diffuse reflection?
and give an example
when a wave is reflected by a rough surface and the reflected rays are scattered in lots of different directions
e.g. a piece of paper
What causes an object to appear
matte vs shiny?
When light is reflected by a rough surface, the surface appears matte as you don’t get a clear reflection
(the opposite occurs with smooth and so shiny objects)
What are
electromagnetic waves?
transverse waves that come from vibrations of electrical and magnetic fields
this means that they can travel through a vacuum
What do
electromagnetic waves do?
and give an example.
they transfer energy from a source to an absorber
e.g. a hot object transfers energy by emitting infrared radiation, which is absorbed by the surrounding air
What are the
seven basic types of EM waves?
(in order of ascending frequency)
Rich - Radio Waves
Men - Micro Waves
In - Infra Red
Vegas - Visible Light
Use - Ultra Violet
Xpensive - X-rays
Gadgets - Gamma Rays
What is the range of wavelength of
radio waves?
10^4 m - 1m
What is the range of wavelength of
micro waves?
1m - 10^-2 m
What is the range of wavelength of
infra red?
10^-2 m - 10^-5 m
What is the range of wavelength of
visible light?
10^-5 m - 10^-7 m
What is the range of wavelength of
ultra violet?
10^-7 m - 10^-8 m
What is the range of wavelength of
x-rays?
10^-8 m - 10^-10 m
What is the range of wavelength of
gamma rays?
10^-10 m - 10^-15 m
Why is ther such a
large range of frequencies of EM waves?
because EM waves are generated by a variety of changes in atoms and their nuclei
this also explains why atoms can absorb a range of frequencies - each one causes a different change
When does
refraction occur?
when a wave crosses a boundary between materials at an angle and it changes direction
What affects how much a wave is
refracted?
how much the wave speeds up or slows down
(which usually depends on the density of the two materials)
usually the higher the density of the material, the slower a wav travels through it
What happens when a wave crosses a boundary an
slows down?
it will bend towards the normal
(and vice versa - a wave that speeds up will bend away from the normal)
What happens if the wave is travelling
across a boundary between materials along the normal?
it will change speed, but it’s NOT refracted
Describe an experiment that investigates
refraction through different materials.
(6 steps)
- Place a transparent rectangular box on a piece of paper and trace around it.
- Use a ray box or a laser to shine a ray of light at the middle of one side of the block.
- Trace the incident ray and mark where the light ray emerges on the other side of the block.
- Remove the block and, with a straight line, join up the incident ray and the emerging point to show the path of the refracted ray through the block.
- Draw the normal at the point where the light ray entered the block. Use a protractor to measure the angle of incidence and the angle of refraction
- Repeat this experiment using rectangular blocks made from different materials, keeping the incident angle the same throughout.
How can you produce
radio waves?
- EM waves are made up of oscillating electric and magnetic fields.
- Alternating currents are made up of oscillating charges. As the charges oscillate, they produce oscillating electric and magnetic fields (EM waves).
- Radio waves are produced using an alternating current in an electrical circuit.
How are
radio waves transferred?
(4 steps)
- The transmitter oscillates electrons to create the radio waves.
- When the transmitted radio waves reach a receiver, the radio waves are absorbed.
- The energy carried by the waves is transferred to the electrons in the material of the receiver.
- This energy causes the electrons to oscillate and (if the receiver is part of a complete electrical circuit) it generates an alternating current.
this current has the same frequency as the radio wave that generated it
What is the main use of
radio waves?
communication
What are the wavelengths of
radio waves?
long-wave radio?
short-wave radio?
radio: >10cm
long-wave: 1-10km
short-wave: 10-100m
How far can
long-wave radio be transmitted?
and why?
they can be transmitted halfway around the world because long wavelengths diffract (bend) around the curved surface of the Earth
What is the
ionsphere?
an electrically charged layer in the Earth’s upper atmosphere
How far can
short-wave radio signals be transmitted?
and why?
they can be transmitted large distances because they are reflected from the ionsphere
Why must you be in
direct sight of the transmitter to get reception for TV and FM radio?
because the transmissions have very short wavelengths that cannot bend or travel far through buildings
What types of wave does
communication to and from satellites use?
and why?
microwaves
they can pass easily through the Earth’s water atmosphere
What is the journey of a signal for
satellite TV?
(3 steps)
- The signal is sent from a transmitter into space.
- A satellite receiver dish orbiting thousands of kilometres above Earth picks this up. The satellite transmits the signal back to Earth in a different direction.
- A satellite dish receives this on the ground.
There is a slight time delay between the signal being sent and received because of the long distance the signal has to travel.
How do
microwaves work?
(3 steps)
- The microwave oven releases microwaves.
- These penetrate a few centimetres into the food before being absorbed and transferring the energy they are carrying to the water molecules in the food, causing the water to heat up.
- The water molecules the transfer this energy to the rest of the molecules in the food by heating - which quickly cooks the food.
What is
infrared radiation?
radiation that is given out by all hot objects
the hotter the object, the more IR radiation it gives out
How do
electric heaters work?
(3 steps)
- Current flows through a long piece of wire that heats up.
- This wire emits a lot of infrared radiation.
- The emitted IR radiation is absorbed by objects and the air in the room - energy is transferred by the IR waves to the thermal energy stores of the objects, causing their temperature to increase.
What are
optical fibres?
and how do they work?
they are thin glass or plastic fibres that can carry data over long distances as pulses of visible light
the light rays are bounced back and forth by reflection until they reach the end of the fibre
What is
fluorescence?
a property of certain chemicals where UV radiation is absorbed and then visible light is emitted
How do
fluorescent lights work?
and why are these good?
- The lights generate UV radiation.
- This is absorbed and re-emitted as visible light by a layer of phosphor (on the inside of the bulb)
they’re very energy-efficient
How is an
x-ray image created?
It’s the amountof radiation that’s not absorbed that gives you an X-ray image.
X-rays pass easily through flesh but no so easily through denser material like bones or metal.
What are
two uses of x-rays?
- seeing if someone has any broken bones
- treatment for cancer
What are the effects of each type of radiation when it
enters living tissue?
(categorised by frequency)
- Low frequency waves (e.g. radio waves) mostly pass through soft tissue without being absorbed
- High frequency waves (UV, x-rays, gamma rays) transfer lots of energy and so can cause lots of damage
What are the effects of
UV radiation enterring living tissue?
(general + 4 consequences)
It damages surface cells.
This can lead to:
- suburn
- skin aging prematurely
- blindness
- increased risk of skin cancer
What are the effects of
x-rays or gamma rays enterring living tissue?
(general + 3 consequences)
It can knock electrons off atoms.
This can lead to:
- gene mutation
- cell destruction
- cancer
What is
radiation dose?
and what is this measured?
a measure of the risk of harm from the body being exposed to radiation
this is measure in sieverts (Sv)
What is the
axis of a lens?
a line passing through the middle of the lens
What does a
convex lens do?
It bulges outwards, causing rays of light parallel to the axis to be brought together (converge) at the principal focus.
What does a
concave lense do?
It caves inwards, causing rays of light parallel to the axis to spread out (diverge).
What is the
principal focus?
(in both concave and convex lenses)
conex lens - where rays hitting the lens all meet
concave lens - where rays hitting the lens appear to all come from
Define
focal length.
the distance from the centre of the lens to the principal focus
What are the three key things to mention when
describing an image?
- How big it is compared to the object.
- Whether it’s upright or inverted relative to the object.
- Whether it’s real or virtual.
How is a
convex lens represented in ray diagrams?
a y-axis
(vertical line with arrow heads on either side)
How would you
draw a ray diagram for an image through a convex lens?
(6 steps)
- Pick a point on the top of the object.
- Draw a ray going from the object to the lens parallel to the axis of the lens.
- This ray is refracted through the principal focus (F) on the other side of the lens.
- Draw another ray from the top of the object going right through the middle of the lens. (This ray doesn’t bend.)
- Mark where the rays meet. That’s the top of the image.
- Repeat the process for a point on the bottom of the object.
How does
distance from the lens affect the image for a convex lens?
(an object at 2F, between F and 2F and nearer than F)
- an object at 2F will produce a real, inverted image the same size as the object, and at 2F (on the other side of the lens
- an object between F and 2F will make a real, inverted image bigger than the object, and beyond 2F
- an object nearer than F wil make a virtual image the right way up, bigger than the object, on the same side of the lens
How is a
concave lens represented in ray diagrams?
a vertical line with an arrow head pointing inwards on each side
How would you
draw a ray diagram for an image through a concave lens?
(6 steps)
- Pick a point on the top of the object.
- Draw a ray going from the object to the lens parallel to the axis of the lens.
- This is refracted so that it appears to have come from the principal focus. Draw a ray from the principal focus. Make it dotted before it reaches the lens.
- Draw another ray from the top of the object going right through the middle of the lens. (This lens doesn’t bend.)
- Mark where the refracted rays meet. That’s the top of the image.
- Repeat the process for a point on the bottom of the object.
What are the rules surrounding the
image produced by a concave lens?
A concave lens always produces a virtual image. The image is the right way up, smaller than the objet and on the same side of the lens as the object.
The further an object is from the lens, the smalle the image produced.
What is the
formula for magnification?
magnification = image heigth / object height
I = AM
What are the three
primary colours of light?
red
green
blue
What are
opaque objects?
objects that do not transmit light
they absorb some wavelengths and reflect others
transparent and translucent objects transmit light
What wavelengths of light are reflected for an object that is
not a primary colour?
(2 options)
- the wavelengths of liht corresponding to that colour are reflected
- the wavelengths of the primary colours that can mix together to make that colour are reflected
What wavelengths of light do
white objects reflect/absorb?
they reflect all of the wavelengths of visible light equally
What wavelengths of light do
black objects reflect/absorb?
they absorb all of the wavelengths of visible light
your eyes see black as the lack of any visible light
What is a
transparent or translucent object’s colour related to?
the wavelengths of light transmitted and reflected by it
How does
temperature affect how much IR radiation an object emits and absorbs?
- an object that’s hotter than its surroundings emits more IR radiation han it absorbs as it cools down
- an object that’s cooler than its surroundings absorbs more IR radiation than it emits as it warms up
- objects at a constant temperature emit IR radiation at the same rate that they are absorbing it
How do
colour and surface finish affect how well at absorbing and emitting radiation an object is?
black + matte - better at absorbing and emitting radiation
white + shiny - worse at absorbing and emitting radiation
Describe a practical that
investigates IR radiation emission with a Leslie cube.
(6 steps)
- Place an empty Leslie cube on a heat-proof mat.
- Boil water in a kettle and fill the Leslie cube with boiling water.
- Wait for a while for the cube to warm up, then hold a thermometer against each of the four vertical faces of the cube. (These should all be at the same temprature.)
- Hold an infrared detector a set distance away from one of the cube’s vertical faces, and record the amount of IR radiation it detects.
- Repeat this measurement for each of the cube’s vertical faces.
- Do this experiment more than once, to make sure your results are repeatable.
Define
perfect black body.
an object that absorbs all of the radiation that hits it
no radiation is reflected or transmitted
these are also the best possible emitters of radiation
What is the relationship between
temperature and intensity of wavelengths emitted by an object?
as the temperature of the object increases, the intensity of every emitted wavelength increases
the intensity increaes more rapidly for shorter wavelengths
What happens to
radiation from the sun that reaches Earth’s atmosphere?
- some radiation is reflected by the atmosphere, clouds and the Earth’s surface
- some radiation is absorbed by the atmosphere, clouds and the Earth’s surface
- some radiation is also emitted from each surface
What type of wave are
sound waves?
longitudinal waves
sound waves are caused by vibrating objects
Describe how you
hear sound?
(when your ear drum vibrates)
- Sound waves reach yourm ear drum and cause it to vibrate.
- These vibrations are passed on to tiny bones in your ear called ossicles, through semicircular canals and to the cochlea.
- The cochlea turns these vibrations into electrical signals which get sent to your brain and allow you to sense the sound
What is the range of frequencies a
human ear can hear?
20Hz - 20kHz
When are
sound waves reflected?
when they hit a hard flat surface
When are
sound waves refracted?
when they enter different media
as they enter denser material, they speed up
What is
ultrasound?
sound with frequencies higher than 20 000Hz
What is
partial reflection?
when a wave passes from one medium into another and some of the wave is reflected off the boundary and some is transmitted
What are
three uses of ultrasound?
- medical imaging
- industrial imaging
- echo sounding
How can ultrasound be used in
medical imaging?
(2 steps)
- Ultrasound waves can pass through the body, but whenever they reach a boundary between two different media (e.g. fluid in the womb and the skin of the foetus) some of the wave is reflected back and detected.
- A computer can process the exact timing and distribution of these echoes to produce video image of the foetus.
How can ultrasound be used in
industrial imaging?
(2 steps)
- Ultrasound waves entering a material will usually be reflected byt the far side of the material.
- If there is a flaw such as a crack inside the object, the wave will be reflected sooner.
this helps to find flaws in objects
What is
echo sounding?
the use of ultrasound to find out the depth of the water a boat or submarine is in
What are the
two different types of seismic waves?
(that you need to know)
P waves and S waves
How are
seismic waves created?
when there’s and earthquake somewhere, it produces seismic waves which travel through the Earth
How are
seismic waves detected?
using seismometers
What are the key characteristics of
P-waves?
(4)
- type of wave?
- types of substances they can travel through?
- relative speed?
- can they travel through the Earth’s core?
- they are longitudinal
- they travel through solids and liquids
- they travel faster than S-waves
- they can travel through the Earth’s core
What are the key characteristics of
S-waves?
(4)
- type of wave?
- types of substances they can travel through?
- relative speed?
- can they travel through the Earth’s core?
- they are transverse
- they can’t travel through liquids or gases
- they’re slower than P-waves
- they cannot travel through the Earth’s core
