p5 Flashcards
which type of wave is transmitted through space where they all have the same velocity?
transverse waves
how are electro magnetic waves transfered?
from sources (sun/microwaves) to absorber (skin/food)
list the electromagnetic spectrum:
(increasing frequency)
- radiowaves
- microwaves
- infrared light
- visible light (red to violet)
- ultraviolet
- X rays
- Gamma rays
why can our eyes only detect visible light?
our eyes are only sensitive to the range of frequencies that we call visible light
visible light is not absorbed by the atmosphere
what type of wave is light?
an electromagnetic wave
give examples of some of the practical uses of the electro magnetic spectrumm
- radio=communication via TV and radio
- micro=microwave oven cooking food, statelite communications
- infrared=electrical heaters, cooking food in grill/oven,
- visible =fibre optics communication, lasers
- UV= makes vitamin D, forensics, detecting false bank notes
- Xray =medical imaging (radiography)
- gamma = medical treatment for cancer
how are gamma , X rays and ultraviolet waves hazardous ?
(ionises cells )
* UV, damages DNA in cells of skin, cells grow rapidly and cause skin cancer
* X rays
how can UV, X rays and gammaβs harzards be utlisied?
- UV : can kill bacteria and sterlise
- X rays: can kill skin cancers
- gama can kill cancer cells and bacteria on food
How are infrared waves used for medical imaging?
- thermal imaging camera produces a thermogram(shows regions of differnt tempratures)
- pixels inside a CCD (Couple charged device) absorb infrared and produce an image
- shows problems with blood flow and vessels
skin will emit more infrared if injury
how are X rays used for medical imaging?
- bones absorb X rays, but tissues, skin , muscle do not
- the photographic film darkens when it absorbs X rays (hence bones white as they absorbed the X rays)
How are CTs and CCDs used with X ray?
- CCD: absorb the x rays and colour depending on intensity. The more dense a material is the more X Rays they absorb/ This can then be used to produce computerised tomogrpahy
how are gamma rays used in medical imaging?
- radioactive substance (tracer) is injected into the body
- the kidneys will absorb the tracer
- the gamma rays are then emmited out of the body
- CCDs then produce an image
how are radio waves produced?
- ossilactions in electrical circuits
(chaning electric and magnetic field)
how do different substances react to electrmagnetic waves?
- absorb (depending on wavelength/frequency)
- transmit
- refract/ reflect
how does a prisim split white light into a continous spectrum?
- each frquency of light travles at slightly different speeds in glass
- so refract by different amounts (higher frequnecy = higher refraction)
what determines if a material can reflect or not?
if refelction is
* specular (sharp image)
* diffused
describe amplitude
distance from normal line to maximum displacement
describe wavelength
distance from one point on a wave to the same point on the next wave
describe frequency
the number of waves that pass a point in one second
describe the time period
the amount of time taken for one wave to pass
describe the realtionship between wavelength, frequency and wave velocity
(m/s)
describe the realtionship between time period and frequency
what are the differences between longitudinal and transverse waves?
- longitudunial: direction of energy transfer is parallel to direction of vibration
- transverse: the direction of energy transfer is perpendicular to direcrion of vibration
what happens to sound waves when they cross a boundary?
in terms of velocity, frequency and wavelength
when traveling from medium to another velocity and direction can change (refraction)
when travelling into a more dense region: (waves speed up)
* wavelength : moves away from normal, so wavelength increases
* velocity: increases due to chnage in medium (density)
* frequency: always stays the same
what three things can happen when a wave hits the boundary between 2 media?
- absorption
- transmitted (refracted)
- reflected
what is ultrasound and why is it useful?
- ultrasound operates above 20,00Hz,
- useful because it has a very small wavelngth and so can focus it into a beam
Describe the process of ultrasound
image of a foetus
- transmitter beams ultrasounds into the mother
- the waves reflect from the different boundaries
- the machine calculates the distances by using time and velocity to produce an image
what happens when a sound wave hits a solid?
- sound is absorbed making particles vibrate
- solid gets a bit hotter
describe how the ear detect sound?
- pinna and ear anal dircet the sound wave to the ear drum
- ear drum vibrates, making the ossicles vibrate
- the ossicles amplify the vibration and passes it on to the inner ear through oval window
- the cochlea contains afluid which transmits the vibration and makes amll hairs inside the cochlea vibrate
- the hairs are attached to sound detecting cells that release chemical substances
- makes nerves send a signal down auditory nerve to the brain
why does hearing change due to ageing?
you lose the shorter hairs and so it is more difficult to hear higher frequencies
human hearing= 20 - 20,000 Hz
how are ripples on water surfaces used to model transverse waves?
- the surface of the wave moves up and down
- the wave travels but the water does not
how do you calculate the speed of transverse waves?
wavespeed= frequnecy * wavelength
* wavelength: using a flashlight /ruler
* frequency: number of roatations of motor per second
how do you measure the speed of sound
speed= distance/ time
distance: ruler/ trundel wheel from wall to person
time: stopwatch from clap to when echo is heard
describe how oscilliscope practical works?
How do sound waves travel in the different states of matter?
Least in gas, highest in solids
This is because the particles are closer together
What is the normal line?
The mean position of a particle, about which it vibrates and oscillates
What are compressions?
Particles squashed together
High pressure
PEAKs
What are rarefactions?
Particles spread far apart
Low pressure
Troughs
What is the formula for wave speed?
Wave speed = frequency βοΈwavelength
C= f βοΈΔ― (iambs)
Wave speed =m/s
Frequency =hertz (Hz)
Wavelength = m
What is the time period?
The time taken to produce 1 wave,
The equation is 1/ frequency = TP
1/TP= frequency
What is the only variable that can change the velocity of a wave?
The medium it is travelling , not the energy transferred
What does amplitude correspond to in sound?
The larger the amplitude, the larger the volume
How are electro magnetic waves created?
Vibrating charged particles
What is the difference between sound waves and EM waves?
Sound = vibrating particles
Transfer kinetic energy
EM= vibrating charged particles
Transfer electromagnet energy
What is the speed of light?
3 βοΈ10^8
All EM waves travel at this speed
How are sound waves produced?
vibrating particles,
colliding with neighbouring particles,
transferring energy
how are electromagnetic waves produced?
vibrating charged particles,
oscillating electrostatic field,
moving magnetic filed
transfers electro magnetic energy
What is an ultrasound wave?
A wave that operated above 20,00Hz and so cannot be heard by humans , harmless to babies
How are ultrasound scans produced?
- (Def) a transducer is a device that produces ultrasound waves by causing a crystal to vibrate rapidly.
- (Process) the transducer emits a pulse of ultrasounds
These waves are partially reflected every time they cross a boundary between different media.
The reflected ultrasound waves return to the transducer as a series o pulses which are deciphered to form an image.
Why are ultrasounds used to produce an image of motherβs womb?
Non -ionising (harmless to Fetus )
Reflected easily at boundaries, can clearly image soft tissue
Describe the following oscilloscope trace
What is reflection?
When a wave reverses direction upon meeting the boundary between two media
What is the law of reflection?
The angle of incidence is equal to the angle of reflection, when the surface is smooth
Why use ultrasound instead of X rays
ultrasound waves are harmless sound waves which operate at a frequency above 20,000Hz (non -ionising)
X rays are a type of electromagnetic wave , with a high frequency that is ionising. This means that it could kill or damage some of the babies cells.
Ultrasound waves are easily reflected at boundaries, allowing some of the soft tissue and internal organs of the baby to be shown.
What is refraction?
When a wave changes direction, upon crossing the boundary between two media
In which media does light travel the fastest , and slowest
What is refraction ?
As a wave crosses the boundary between two media itβs speed and direction changes
(Observed to the eye to bend)
Draw a reflection diagram
Draw how an image is formed in a mirror
What is the difference between an inverted and upright image ?
A inverted image is upside down
What is the difference between a virtual and real image?
A virtual image is basically imaginary, it is an image produced by a mirror that appears to be present , but cannot be seen on a screen.
However a real image is an image that you can put on a screen
rule of refraction
When a wave is travelling from a less dense to more dense medium?
The ray slows down and so moves towards the normal
rule of refraction
When a wave is travelling from a more dense to more less medium?
Speeding up , and so move towards the normal
Complete the diagram
What happens to the wave length of waves as they enter a more dense medium
why are the shapes of concave and convex lenses ?
what do concave lenses do ?
What do convex lens do ?
describe short sightedness
Diverging rays which enter the ray are too converged
So are focussed before the retina
describe long sightedness
Cannot focus parallel rays from far away as lens is too weak to converge
Focused behind the retina
What is a real image
An image that is formed where the light rays meet.
The object is outside the focal length of a converging lens
What is a virtual image ?
An image that is formed where the light rays appear to come from.
The image formed inside the focal length for a converging lens.
When does an image appear magnified?
When an object is placed inside the focal Lemgo of a converging lens
Draw an object placed outside the principal focus for a convex lens
Draw an object placed inside the principle focus for a convex lens
Draw an object placed outside the principal focus for a concave lens
What is dispersion?
The separation of white light into itβs constditutent wavelengths .
This occurs because the different EM radiation have different frequencies and travel and different speeds , and so the angle of refraction differs. (The higher the frequency ,the higher the angle of refraction )
How do you perceive a colour ?
Eg this blue π¦
The object is absorbing all other frequencies , but is then only reflecting that frequency (blue ). For this to be seen
What are filters ?
Eg a blue filter π¦
Will absorb all frequencies but will transmit others (blue )
*filters must be transparent
What colour light will be shown at the end ?
Diverging
Separates the light rays, further away from each other
(concave lenses)
Converging
Bring the rays closer together
(convex lenses)
What are the primary colours?
