Waves - Y10 Flashcards
What are waves?
They transfer energy from 1 place to another without transferring any matter
Give an examples of a transverse wave
- Ripples on a water surface
- EM Waves
- Wave on a string
Give an examples of a longitudinal wave
- Sound waves
- Shock waves
What are transverse waves?
- Oscillations are perpendicular (90’) to the direction of the energy transfer
- Oscillations (vibrations) are up and down
- Energy transfer is sideways
What are longitudinal waves?
- Oscillations are parallel to the direction of energy transfer
- Consists of compressions & rarefactions
- Need a medium to travel in e.g air, solid, liquid
Amplitude
The maximum displacement of a point on the wave from its undisturbed point (height)
Wavelength
Distance between the same point on 2 adjacent waves
Frequency
Number of waves passing a point each second
What does 1 Hz mean?
1 wave per second
Period
Time (seconds) for one wave to pass a point
How do you find the period?
Period(s) = 1/ frequency (Hz)
What is the wave speed?
Speed at which energy is being transferred or speed the wave is moving at through the medium
Equation for speed (units)
v = λ f
wave speed (m/s) = wavelength (m) X frequency (Hz)
What 3 things can happen to a wave? What does this depend on?
- Absorbed by the material (transfers energy to the material’s energy stores)
- Transmitted (goes through the material, gets refracted and carries on moving)
-
Reflection
These depend on the wavelength and properties of the materials involved
What is the rule for all reflected waves?
Angle of incidence = angle of reflection
What degree is the normal always at in a ray diagram?
90’
What is specular reflection?
- Happens on a smooth surface
- Wave is reflected in a single direction
What is diffuse reflection?
- Happens on a rough surface
- Reflected rays are scattered in lots of different directions
- All have different mediums
What are EM waves?
Electromagnetic waves are:
* transverse waves
* they transfer energy from a source to an absorber
* They all travel at the same speed through air or a vacumm
* Dont need a medium to travel in
How does density affect the speed of a wave?
Higher density = slower wave travels through it
Low density = faster wave travels through it
Light travelling from a less dense material, into a more dense material, will bend ________ the normal.
towards
What happens when a wave slows down?
Include density
When it goes through a high density object, it will bend towards the normal
What happens when a wave speeds up?
Include density
When it goes through a low density object, it will bend away the normal
Ray diagrams: What happens if the 2nd material optically denser than the 1st?
Refracted ray bends towards normal - angle between refracted ray and normal is smaller than angle of incidence
Ray diagrams: What happens if the 2nd material is less optically dense than the 1st?
Angle of refraction is larger than angle of incidence (away from normal)
Electromagnetic spectrum in order
Describe the freq and wavelength
- Radio waves - Low freq, longer wavelength
- Micro Waves
- Infra Red
- Visible Light - only seen by human eye
- Ultra Violet
- X-Rays
- Gamma Rays - higher freq, shorter wavelength
What speed do EM waves travel at in a vacuum?
3 x 10⁸ m/s
How to you find the frequency?
Number of waves / time
How many Hz is 1MHz
1000000 (6)
2 types of waves formed from earthquake
Seismic waves called P and S waves
How do you detect waves from an earthquake
seisomemteres
What are P-waves?
- Longitudinal
- Travel through solids and liquids and gases (fastest in solids)
- faster than s waves
- pass through core
What are S waves?
- Transverse
- Travels only in solids
- Slower than P waves
- Travels in curved lines
What is the S wave shadow zone?
- Where no S waves can be detected
- Because S waves cant pass through a liqiud - tells us Earth has a liquid core
What is the P-wave shadow zone?
- Where waves cant be detected
- Because P waves travel faster in solids than in liquids - tells us P waves slow down as they enter the liquid outer core - caues them to refrcat
- They also refract when they leave outer core = outer core is liquid
Normal human ear frequency
20 - 20,000 Hz
What is ultrrasound
Soundwaves with higher frequency than upper limit of human hearing 20,000Hz
What happens with ultrasound waves and why?
- Get partially reflected at the boundary between 2 diff densities - partial reflection
Equation for distance using ultrasound
s = vt
(m) = (m/s) X (s)
How would you find out the depth using the ultrasound distance equation?
Substitute then divide by 2 so get depth, otherwise you would get the total + reflected distance
Uses for ultrasound
- Medical imaging eg pre-natal scaaning of a foetus
- Industrial imaging eg finding flaws in materials/ hidden defects/ problems with a weld
How does ultrasound work in medical imaging?
- Wves can pass through the body but when they reach a boundary between 2 diff media (womb fluid and skin of foetus), some wave is reflected back and detected
- Exact timing and distribution of these echoes are processed to make a video image
How is ultrasoud used in industrial imaging?
- Used to find flaws in pipes, wood, metal
- Waves entering a material will usually be reflected from the farside of the material
- If there is a crack, it would be reflected sooner
What is echo sounding?
- Uses high frequency sound waves
- Used by boats and submarines to find out the depth of water
- Or to locate objects in deep water
What are sound waves caused by?
Vibrating objects - vib. passes throught the surrounding medium as a sreies of compressions and rarefactions
Where does sound travel faster in?
In solids than liquids
In liquids than gases
What happens when a sound wave travels through a solid?
Causes particls to vibrate
Can sound travel in space, why?
No, mostly a vaccum, no particles to move/vibrate
How do you hear sound, steps?
- Sound waves reach ear drum, causes it to vibrate
- Vibrations -> ossicles (small bones) -> semicircular canals -> cochlea
- Cochlea turns vib. to electrical signals -> brain, allow yuo to sense the sound
Where will sound waves be reflected, what does that cause?
Refleted by hard flat surfaces = reflected sound waves = echoes
When do sound waves refract? What happens when they enter a dense thing, why?
When they enter diff media
Denser material = speed up because wavelength changes, but frequency stays the same, so speed must also change
What are radio waves used for?
used to transmit radio and terrestrial TV Signals
What is terrestrial TV?
Not satellite or cable TV, received using an aerial
Why are radiowaves used?
- Can travel long distances befroe being absorbed by buildings/trees
- Longer wavelength radio waves can also spread out between hills (diffraction)
- Can reflect off a layer of charged particles in the atmosphere (ionosphere) - allows us to send v long distances around the Earth
Uses of microwaves
Heating food, communication with satellites in space
Why are microwaves used for heating food?
- Most food contain water molecules
- Water molecules absorb the energy of microwaves
- Energy causes temp of food to increase
Why are microwaves used to com. with satellites in space?
- Can pass through Earths atmosphere without being reflected or refracted
Uses of infrared
- Emitted by electrical heaters
- Cook food in ovens
- Infrared cameras
Why is infrared used in heaters?
Energy of infrared is easily absorbed by the surface of the objects. Makes the room warmer as infrared is absorbed
Uses of visible light
- Com. using fibre optics (in telephones and cable TV signals)
How do optical fibres work?
- Transmit pulses of light down fibres and use pulses to carry info
Why is visible light used in optical fibres?
Short wavelength allows it to carry lots of info
Uses of UV
- Energy efficient lightbulbs
- Suntanning
How do energy efficient ligtbulbs work?
- UV light made in the bulb
- UV has a shorter wavelength, carries more energy than visible light
- Energy of UV is absorbed by the internal surface of the bulb and is converted to visible light
- This requires less energy than a normal light bulb
Negatives of UV
Premature skin aging, increases risk of skin cancer
Uses of gamma and x rays
- Medical imaging
- Med treatments eg cancer
- Gamma = detect cancer
X rays = visualise broken bones
Why are gamma and x-rays used in medical imaging?
Both rlly penetrative, can easily pass through body tissue
How do X-ryas work in MI?
Absorbed by bones
What do lenses do?
Refract light
What are convex lenses?
- Bulge outwards
- Thicker in the middle
- Produce real and virtual images
- Causes rays of light to converge at a focal point
What are concave lenses?
- Rays of light diverge
- Always produce virtual images because of light rays appear to come from the nearside focal point
- Lenses go inwards
Sign for convex?
↕
Sign for cancave?
Inward facing arrows
2 important facts about parallel rays of light passing through a convex lens
- Central ray passes through the lens without being refracted because this ray is passing directly along the normal, its passing along the principal axis
- All other rays refract and are focused on a point (Principal focus) - F
Principal focus
Where all other rays focus
What is the principal axis?
Centre of the lens
Focal length
Distance from centre of lens to principal focus
What is a real image? How is it diff to a virtual
Real = rays acc meet
Virtual = they dont, make a dashed line backwards
6 feautures an image can be on a ray diagram
- Diminished/Magnified
- Inverted/ right way up
- Real/Virtual
Object is more than 2 focal lengths from lens
- Image is dimished, inverted,real
Object between 1 and 2 focal lengths from lens
- Image is magnified, inverted, real
What surface is the best absorbers and emitters of infrared radiaiton?
Matt black surfaces
What 2 things depend on the temp of the object?
Wavelength and intenisty of radiation
What length wavelength do v hot objects emit?
Shorter
What happens to the radiation when temp increases?
Intensity of radiaiton
increases
What is a perfect black body?
Absorbs all the radiation incident on it
* No radiation reflected or transmitted
* Best possible emitter of radiation
What happens if an object is warmer than its surroundings?
- Emit more radiation than it absorbs
- Temp of object decreases
What happens if an object is cooler than its surroundings?
- Absorb more radiation than it emits
- Temp increases
What happens if an object is at a constant temp to its surroundings?
- Absorbing rad. at the same rate as it is emitting rad.
How does the Earth lose/gain energy?
By absorbing or emitting rad
How does the Earth’s temp increase?
- Sun emits short wavelength rad (UV/ visible light)
- Travels to eaarth
- Some is reflected by clouds
- Remaining rad is absorbed by surface of earth
- Causes temp to increase
- EARTH EMITS INFRARED RAD BACK INTO SPACE
- Some energy of infrared is trapped by greenhouse gases
Why do very hot objects produce visible light?
Because as an object gets hotter, the wavelength becomes shorter
Which is warmer? Cloudy nights or clean nights? Why?
Cloudy - clouds can reflect infrared back to the Earth and prevent it being radiatied into space
What travels in both transverse and longitudinal waves?
The wave and not the water or the air
RP 8
What is a ripple tank used for?
to observe the feautrues of water waves
RP 8
Describe a ripple tank
- Shallow tray of water.
- In the water is a vibrating bar connected to a power pack.
- When bar vibrates, creates waves
- A lamp above ripple tank
Below ripple tank is white paper
RP 8
What happens when line shines through the water?
It produces an image of the waves on the paper
RP 8
What is the easiest way to record waves?
Using a mobile phone = you can play back the recording at diff speeds or freeze image
RP 8
Method
- Ruler on paper -> measure distance between one wave and 10 waves further (10 wavelength eg = 0.26m)
- Find one wavelength divide by number of waves counted for each wavelength
- Calc freq = place timer next to paper and count no of waves passing a point in 10 s then divide by 10
- Use v= f lambda
How calc freq?
no of waves / time
RP 8 Waves in a solid
Apparatus
- mass
- pulley on clamp
- wooden bridge
- string
- vibration generator
- signal genetator
What does the signal generator do?
allows us to change freq of vibration of string
RP 8 Waves in a solid
What is a standing wave?
Wave caused by resonance
RP 8 Waves in a solid
Method to measure wave speed of standing wave
- Measure wavelength using ruler from wooden bridge to vibration generator
- Read freq from signal generator
- Use v=f Lambda
RP 8 Waves in a solid
What happens in you increase the freq in a standing wave?
- More no of half wavelengths
How would you calculate wavelength of 3 1/2 wavelengths?
- Find total distance of the wavelengths by measuring ruler form wooden bridge to vibration generator
- Divide that by no of half wavelengths then X2
Does the wavespeed of the string depend on freq or wavelength?
no, it depends on taughtness of string and mass per cm
RP 9 Reflection and refraction
Apparatus
- Ray box
- lens
- slit
- glass box
RP 9 Reflection and refraction
Method
- Take piece of a4 paper and straight straight line down centre with ruler
- Use protractor to draw a line at right angles = normal
3.Place glass block against first line so normal is near centre of block
4.draw around glass block
5.turn lights off in room
6.use ray box to direct ray of light so it hits block at the normal = incident ray
7.Angle between incident ray and normal = angle of incidence
8.adjust ray box and change engle of incidence = at a certain angle, we can see ray reflect from surface of the block + transmitted ray leaviing block
9.Mark path of incident ray and relfected ray + transmitted ray with crosses
10.Remove block and turn on lights, draw and join trnasmitted ray to centre of block - Protractor and measure angles (incidene and reflection and refraction (between normal and transmitted ray))
- Repeat with diff material block
Why may we not be able to hear frequencies between 20 - 20,000 Hz
may not be able to cause eardrum to vibrate
Why does sound travel faster in solids?
Particles close togther = vibration can pass more easily between them than gases
What also changes when the wavespeed changes as waves pass from 1 medium to another?
wavelength eg is wavespeed up, wavelength up
What does not change when a wave changes medium?
freq cuz they would have to be destroyed/created at the boundary which isnt possible
How can we view the features of a sound wave?
Name a prob with this
- connecting a microphone to a cathode ray oscilloscope
- Represents sound waves as if they were transverse waves which they arent
High freq =
low freq =
high pitch
low pitch
small amplitude
large amplitude
quiet
loud
What can sound waves only move through and why?
A medium eg air or a solid beacuse sound waves move by particles vibrating so they cant pass through a vacuum
What do ultrasound only work on?
anything not surrounded by bone
Why is ultrasound safer than X rays?
Doesnt cause mutations and doesnt increase risk of cancer
Layers of the earth and their state
- Inner core (solid)
- Outer core(liquid)
- Mantle(solid but upper mantle can flow)
- Crust (thin solid)
How do scientists know the structure of the earth?
Earthquakes
* Sudden movement between tectonic plates in crust
* causes seismic waves which carry energy away from earthquake
* these pass through earth and be detected by seismometres in diff countries
* patterns of these waves gives info about interior
Why do seismic waves travel in curved paths?
due to density changes in the earth
How do scientists know that the Earth has a solid inner core?
Sometimes faint P waves can be detected in shadow zone = solid inner core
What type of spectrum is the EM spectrum?
- continous spectrum
- cut-off point between one type of wave and other is not always clear
When do waves change direction (refract)?
when they change speed, moving from 1 medium to another
When do wave not refract?
when waves enter/leeave medium at right angles to the surface/along normal
What is the wavefront?
imaginary line that connects all the same points in a set of waves
rp 10
What 4 diff surfaces does the Leslie cube have?
- shiny metallic
- white surface
- matt black
- shiny black
rp 10
Method
- Fill Leslie’s cube with hot water
- Point an infrared detector at each of the 4 surfaces and record amount of infrared emitted
- Same distance between the 2 = makes measurements repeatable
rp 10
Leslie Cube results
- Matt black surface releases the most infrared emission
- then shiny black
- then white
- least = shiny metallic
rp 10 - leslie
Method but without an infrared detector
- Use a thermometer with the bulb painted black
- however, resolution (smallest change that can be detected) of thermometer is less than infrared detector
- infrared more likely to detect a diff
rp 10
How would you measure the absorbence of infrared aparatus
- 2 Metal plate - 1 painted shiny metallic and one matt black paint
- On the other side of each plate, use vaseline to attach drawing pin
- Infrared heater between 2 plates
Method: How would you measure the absorbence of infrared aparatus
- Swithc on heater and timer
- temp of metal plates increases as they absorb infrared
- record time it takes for vaseline to melt and drawing pins to fall off
- we see that the drawing pin falls of the matt black plate first as they absorb more infrared
- matt black better at absorbing and emitting infrared
- shiny metallic reflects infrared
What happens when EM waves are generated or absorbed?
changes take place in atoms or in the nuclei of atoms
What happens when we heat atoms? What causes it to generate an EM wave
- electrons move from energy level to a higher one (outwards)
- When it returns to its original energy level it generates em wave (light)
How can a change in the nucleus produce em waves?
- gamma rays can be emitted from nucleus from radioactive atoms
- when emitted, nucleus has less energy than start
How are radiowaves produced?
- produced when electrons oscillate in electrical ciruits
- these radiowaves can be absorbed eg by electrical circuit in an aerial
- when this happens, electrons in circuit oscillate
- creates an ac w/ same freq as radiowaves
what happens when light waves move from air to glass?
slow down as glass is denser, bend towards normal
When is the only time a convex lens produces a virtual image
used as a magnifying glass
If you made light go through a green filter, what colour would you see and why?
Green because all the other colours are absorbed apart from green which is transmitted
Why do white objects appear white?
Because the reflect all the wavelength of visible light equally
Why do black objects appear black?
They absorb all the wavelength of visible light
Why do red objects appear red?
red object absorbs all the colour of white light except red which is reflected
What colour would appear if with red filter and green object?
black as it reflecting no light
What happens to X rays whent hey enter a bone?
They are absorbed
State one use of infrared and microwaves
infrared = fibre optics
microwaves = satelltie com.
What waves need a medium?
All longitudinal
some transverse
What speed do all EM waves travel at in a vacuum?
3 X 10 8 m/s
What can Em waves, in particular which one, can be used to generate smth?
They can generate AC when absorbed by a conductor, especially radiowaves
How do radiowaves generate AC?
What does it allow us to do?
- Transmitter connected to oscilloscope - allows us to see AC
- Its the freq of the AC that determines the freq of the wave that will be produced
- Radio wave generated by transmitter
- Detected by receiver - absorbs enegry and generates an AC - attached to another oscilloscope where its displayed
Allows us to transfer info
3 types of radiowaves
- long waves - huge distances - they bend around curved surface
- short waves - long distances - reflect on atmosphere
- very short waves - short distances - bluetooth - tv
*
As the temp of an object increases, what happens to the wavelength of radiaiton emitted by the object
it decreases
What are ultrasound waves?
Waves which have a freq higher than the upper limit of human hearing 20,000 Hz
Do EM waves travel at the same speed in air?
Yes
