P5.2 Flashcards
What are electromagnetic waves?
They are transverse waves that are transmitted through space where all have the same velocity. They don’t need particles to travel.
What do electromagnetic waves consist of?
They consist of oscillating electric and magnetic fields. The fields are oscillating in a direction at 90 degrees to the direction of the wave. They are made of photons that travel through space until they interact with matter (some absorbed and some reflected)
What is the EM spectrum
It’s a continuous range of all possible frequency/ wavelength of EM radiation
Name the EM waves from the lowest to highest frequency/energy
- radio waves
- microwaves
- infrared waves (IR)
- visible light (red to violet)
- ultraviolet (UV)
- X-rays
- gamma rays
Rock Music Is Very Useful for eXperiments with Goats
What is the amplitude of an EM radiation the measure of?
It’s the measure of the light intensity (how much energy is arriving in a given time over a given area) (NOT ENERGY)
What does the frequency and wavelength of the light wave determine
It’s determines what colour of light wave it is
What do electromagnetic waves travel through and at what speed.
They travel through a vacuum at 3.0 x 10^8 m/s or 300,000,000 m/s
This is also the speed of light at light is part of the EM spectrum
What are sources and give some examples
Sources (such as the sun or microwave oven) emit EM waves
What do EM waves transfer?
EM waves transfer energy as radiation from sources to absorbers
Some waves like microwaves sent to satellites transfer information
How can you calculate wavelength?
Wavelength (m) = wave speed (m/s) / frequency (Hz)
What happens to the wavelength as you go from red to blue
Red = longest Blue = shortest
What is the spectrum like for white
It’s continuous
It’s part of a wider spectrum called the EM spectrum
What does is means by different waves in the spectrum
It means that there are different bands of frequencies called waves
Name the EM waves from the shortest to the longest wavelength
- gamma rays
- X-rays
- ultraviolet (UV)
- visible light (red to violet)
- infrared (IR)
- microwaves
- radio waves
How do you produce and detect radio waves?
They can be produced by or themselves induce, oscillations in electrical circuits. An oscillating p.d a across a wire makes the e- move back and forth, producing a changing electric and magnetic field which is emitted as a radio wave. When the fields field meet another piece of metal (e.g aerial) then the e- move producing an electrical signal
How are EM waves produced
They are made by the movement of the e- in the atoms. This happens by vibrating charged particles which create an oscillation electrostatic field, which create an oscillating magnetic field and transfer electromagnetic energy
Why can our eyes only detect a limited range of the EM spectrum
Our eyes are only sensitive to a narrow range of frequencies called visible light, which is NOT absorbed by the atmosphere
Why can EM waves travel through a vacuum but sound waves can’t?
Sound waves need particles to vibrate to transfer energy but EM waves don’t ( they travel via oscillating electrostatic and magnetic fields)
How can waving a charged balloon produce a radio wave
When you wave the ballon to give rise to charged particles oscillating at a given frequency. These charged electrons have electrostatic fields around them and oscillating the balloon produces oscillating electrostatic fields. Oscillating electrostatic feels produce a magnetic field and the frequency of oscillation is low enough to match that of a radio wave
How much is a nanometer in meters
10^-9 m
How are sound/ mechanical waves created?
They are created by vibration particles which collide with neighbouring particles and transfer kinetic energy.
Which electromagnetic waves are used for communication and how?
- microwaves are used to communicate with satellites, for Wifi and Bluetooth systems
- radio waves are used in radio and TV by adding sound and picture information to radio waves
- Infrared is used in remote controls and optical wastes
- visible light is used between ships to communicate
How does the microwaves oven heat up food?
The water and the fat in food absorb the microwaves and it can penetrate a few cm into the food. This heats up the inside of the food and then energy is transferred to the middle by conduction.(Faster than ovens/grills)
How do grills/ovens cook food?
Infrared radiation cooks food in a grill or an oven. Infrared from radiation is absorbed by the particles on the surface of the food and they can heat food up by transferring energy to a thermal store. (Slower than microwaves)
What type of electromagnetic wave is used as lasers in CDs/DVDs?
It uses visible light to read the discs
How can UV light be useful for our body and forensic investigations?
- body uses UV radiation from the sun to produce Vitamin D for strong bones
- it can be used in forensics as it can identify bodily fluids and forged bank notes
What three types of electromagnetic waves can damage or kill cells and why is this useful?
Ultraviolet radiation kills bacteria in water and sterilises it
X rays can kill skin cancer or other cancer cells and produce images of bones
Gamma rays can kill cancer cells and also kill bacteria on food we can’t heat up
How can microwaves be hazardous to humans?
It can heat up water and our brain has a lot o f water so you irritate your brain with microwaves when making a call.
How can UV rays be harmful?
It can damage DNA in skin cells. The cells can grow very rapidly and cause skin cancer. Exposing you eyes too much UV can cause you to develop cataracts, which make your corneas cloudy.
How can X- rays be harmful?
They can damage skin cells and cause cancer. A radiographer operating an X - ray machine stands behind a lead screen or in another when the machine is on.
How can gamma rays be harmful?
They can kill and damage healthy cells in the body.
Why can Blu - ray disks store more information that CD that uses red laser light to read it?
Blue has a shorter wavelength than red. This means that the Blu- ray is more precise and so more pits can be closer together, meaning it can store more information.
Why can waves be used for medical imaging?
- wave + boundary = absorb, transmit,refract,reflect
- what happens depends on wave type + media making boundary
- waves can be used to study hidden things -organs
- diff waves = behave diff in body = imaging things
What can X - rays image?
Bones
How can X - rays image bones?
- X- rays = mostly transmitted to soft tissue but absorbed by denser material (bones and metal) + photographic film darkens it
How do CT scans work?
Computerised Tomography
- mostly transmitted by soft tissue, a little bit of X ray is also absorbed = how much X ray is absorbed by soft tissue varies on tissue
- use lots of X -rays = produce high resolution images in 2D and 3D of soft and hard body tissue
- higher density = more X-rays absorbed
What can Gamma rays be used for in the body?
To see how things move through the body
How can gamma rays be used for imaging?
- gamma rays = transmitted by skin, soft tissue and bone
- so if gamma rays are produces inside a patients body they can be detected outside the body
How can gamma rays be detected outside the body?
- radiotracers (radioactive isotopes) that patient swallow/is injected with
- as they move around body = emit gamma rays
- gamma rays are detected by gamma camera to form an image
How do tracers show problems with organs?
- tracers = often part of a molecule that the body uses (glucose containing radioactive carbon 14) so by looking where it send up, doctors can see how the body is working
- cancerous tumours use more energy than healthy tissue to they will absorb more glucose containing the radioactive carbon and show up as bright red spots on image
How can tracers be used in underground pipes?
- find leaks
- detect more gamma rays from a point above the leak than the rest of the pipe
What can Infrared waves tell you about the body?
- injuries and infections
- problems with blood flow in blood vessels
How can Infrared waves show injuries and infections and how is it useful?
- injured/infected areas = hotter than other areas so give off more IR waves
- IR cameras can detect these differences in temp to create image
- useful for taking lots of temp quickly ( used to check people at airports for signs of infection/ fever)
What does a thermal imaging camera produce ?
- image called thermogram = regions of diff temp
- pixels inside charged coupled device (CCD)- phone camera = absorb IR and produce image
- colours added to computer
Why do compromises need to made in medical imaging?
- some waves = dangerous = make compromises
- need good enough image whilst putting as low risk as possible
How are compromises made in ultrasound?
- completely safe
- give fuzzy images
- can only be used for images of soft tissue (not bones)
How are compromises made in X-rays?
- ionising so can cause damage to cells
- give clear images of bones
- CT scans = high resolution images that you can’t get from ultrasound
How are compromises made in gamma rays?
- ionising = cause damage to cells
- can be used to get information on how the body works
How are compromises made in IR radiation?
- completely safe
- don’t tell us much = only temperature
How does Infrared imaging works?
- thermal imaging cameras use IR to produce thermograms
- A CCD absorbs the IR radiation and displays it as a visible colour
- diff colours of visible light are used to indicate the diff intensities of IR
- hotter = emits more IR
How does X-ray imaging work?
- X-rays produce images by showing the contrast (diff in shades) between diff media
- in hospitals - X-rays are used to irradiate a person’s body
- X-rays will pass through soft tissue (low-density medium) but are absorbed by bone (high-density medium)
- X-rays pass through the body and darkens the photographic film
- film is white were X-rays were absorbed by the body and don’t reach the film
How does gamma imaging work?
- radioactive tracer = radioactive compound of an element
- radioactive tracers emit gamma rays usually
- ingested/ injected into the patient and quickly enters the bloodstream
- intensity of gamma radiation emitted is monitored on camera outside
- poor blood flow inside body = less gamma radiation there = possible health problem
What does it mean by ionisation?
- gamma/ beta/ alpha absorbed by molecules
- becomes unstable and have too much energy
- ionises the cells in the body = reactive so they react with the molecules = kills or damages cells
- cancer if continues mutation
How are X-rays different from gamma and IR?
- ## X-rays = not naturally found but gamma (rocks) and IR (anything that’s hot)
What frequency does a warmer object give?
- warmer = higher Hz
- so sun = seems white as it goes from red to white
- if equal no of all frequencies = seems white
What are the safety measures used for X-rays?
- only part of the body that is hurt and keep the rest covered with thick lead
- exposure badge
- lead apron
- lead lining on walls and lead shields
Why do darker skins have a lower chance of getting skin cancer?
- absorb UV
- thus less UV reaches underlying tissue
- more melanin
What waves are reflected by the ionosphere?
Waves under 30GHZ
How should you cook food in a microwave?
- microwaves penetrate few cm into food and absorbed by food and water, which gains ke and heats up
- stir so inner particles redistributed toward the surface so can be reached by microwaves
- standing time = allows time for more conduction or convection to the centre of the food to
Why does a mirror show your image but not a piece of paper?
- Mirror carries out specular reflection and thus it follows the law of reflection of law of incidence=law of reflection
- Paper doesn’t follow the law of reflection and instead scatters light which leave at a different angle from the paper to which they approach the paper
Why does a blue box appear blue?
- white light irradiates the object and absorbs every frequency of light in the EM spectrum except the frequency corresponding to the colour blue
- our brain then perceives this colour as blue
What is black?
- an absence of colour
