3a) Medical Applications of Physics Flashcards
How can X-Rays be used in medicine?
X-Ray Photographs to diagnose bone fractures or dental problems
Describe X-Rays
High frequency
Short wavelength (same as diameter of an atom)
EM waves
Transmitted though healthy tissue
Absorbed by denser materials like bones and metal
What are CCDs
Charge-coupled devices
Silicon chips divided into a grid of millions of identical pixels
Detect X-Rays and produce electronic signals used to form high resolution images
CT scans
Computerised axial tomography
Use X-Rays to produce high-resolution images if soft and hard tissue
Use more X-Rays that’s normal X-Ray photographs to distinguish small variations in tissue density
X-Rays to treat cancer
X-Rays focused in tumour using a wide beam
Beam is rotated
X-Rays cause ionisation which kills the cancer cells
Doesn’t damage normal cells
How do radiographers take precautions to minimise radiation dose?
Wear lead aprons
Stand behind lead screen
Leave the room during scans
Exposure time kept minimum
What is ultrasound
Sound with a higher frequency than we can hear (higher than the upper limit of human hearing)
What is partial reflection
Some of the wave reflected off the boundary between two media
Some is transmitted (and refracted) through the medium
How can ultrasound be used in medicine?
Breaking down kidney stones into sand like particles that pass out of the urine
Pre-natal scanning of a fetus - ultrasound is reflected back from the fetus and detected to form an image
Are ultrasound waves safe?
Yes
Non-ionising
What is the law of reflection?
Angle if incidence = angle of reflection
What causes refraction?
Change in direction of waves
Change in density of one medium to another medium
What happens if a wave hits a boundary at 90 degrees (along the normal)
Will not change direction (won't be refracted) Change speed (slow down)
What is the refractive index of a medium?
Ratio of speed oh light in a vacuum to speed of light in the medium
Refractive index = sin i / sin r
What happens when waves slow down?
They bend towards the normal
Describe the two main types of lenses
Converging lens - convex shape, causes parallel rays of light to converge at principal focus
Diverging lens - concave shape, causes parallel rays of light to diverge (spread out)
What is the axis of a lens?
Line passing through the middle of the lens
What is the focal length?
Distance from the principal focus to the centre if the lens
What is the principle focus for each type of lens?
Converging - where rays meet
Diverging - where the rays appear to come from
Describe real and virtual images
Real image - light from an object comes together to form an image of a ‘screen’
Virtual image - rays diverge so the light appears to come from a different place (e.g mirror, magnifying glass)
What is the word to describe an image that is upside down
Inverted
Laterally inverted - flipped from left to right
How can the nature of an image be described?
How big image is compared to object (magnified/diminished)
Upright or inverted (upside down)
Real or Virtual
What kind of image does a diverging lens produce?
Always virtual image
Describe how distance from the converging lens affects the image
Object at 2F - real, inverted image, same size as object, at 2F
Between F and 2F - real, inverted image, Bigger than object, Further away than 2F
Nearer than F - virtual image, upright, bigger than object, on same side as lens
How is short-sighted vision corrected?
Diverging lens
Causes image to move further back and form on the retina
How is long-sighted vision corrected?
Converging lens
Causes image to move forward and form on the retina
