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Physics (P3) Revision…read more

Slide 2

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Medical application of physics…read more

Slide 3

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X-rays
· X-rays are part of electromagnet spectrum ­ high frequency and very short
wavelength (wavelength = same as diameter of atom)
· Properties of an x-ray
Affect photographic film in the same way as light
Are absorbed by metal and bone
Are transmitted by healthy tissue
· Charge-coupled devices (CDD's) can be used to from electronic images of x-rays,
CT scanners use x-rays to produce digital images of cross section through the
body. Some body organs made of soft tissue, e.g. intestines can be filled with
contrast medium that absorbs x-rays so they can be seen on x-ray image
· X-rays cause isolation and can damage living tissue when they pass through it
therefore precautions must be taken when using them. Workers should wear film
badges and when possible use lead screen to shield them from x-rays
· X-rays may also be used for therapy ­ they can be used to treat cancerous
tumours at or at the surface of the body.…read more

Slide 4

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Ultrasound
· Human ear can detect sound waves with frequencies between 20Hz and 20,000Hz ­ sound
waves of higher frequencies than this are called ultrasound waves
· Electronic systems can be used to produce ultrasound waves ­ when a wave meets a
boundary between 2 different materials, part of wave is reflected, wave travels back through
material to detector. Time taken to reach detector can be used to calculate how far away
boundary is ­ results may be processed by a computer to give image
· Distance travelled by ultrasound pulse be calculate s = v x t
S = distance travelled in m
V = speed of ultrasound wave in metres per second
T = time taken in s
· In the time between a transmitter sending out pulse of ultrasound and it returning to
detector, it has travelled from transmitter to boundary and beck, i.e. twice distance of
boundary
· Ultrasound can be used in medicine for scanning, it is non-ionising so is safer than x-rays to
use. Can also be used for scanning unborn babies and soft tissues such as eye. Ultrasound
may also be used in therapy, e.g. to shatter kidney stones into smaller pieces.…read more

Slide 5

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Refractive index
· Refraction is the change of direction of light as it passes from 1 transparent substance to
another
· Refraction takes place because waves change speed when they cross a boundary ­
change in speed of the waves caused a change in direction ­ unless waves ae travelling
along normal
· Light ray will refract when it crosses from air into glad ­ it is refracted towards normal
· Refractive index of substance is measure of how much substance can refract a light ray
· Refractive index given by equation…read more

Slide 6

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The endoscope
· Light ray will refract when it crosses from glass · An endoscope is device used to look inside a
to air, it is refracted away from normal. A patient's body without cutting it open or when
partially reflected ray is also seen, if angle of
incidence in the glass gradually increases, angle preforming keyhole surgery. The endoscope
of refraction increases until refracted ray contains bundles of optical fibres (very thin,
emerges along boundary. This angle of flexible glass fibres) visible light can be sent
incidence is called critical angle, c. along the fibres by total internal reflection.
· If angle of incidence is increased beyond c light
ray undergoes total internal reflection ­ when · Laser light ay be used as energy source in an
total internal reflection occurs, the angle of endoscope to carry some surgical procedures
refraction = angle of incidence such as cutting, cauterising and burring. The
colour of laser light is matched to type of
tissues to produce maximum absorption. Eye
surgery on retina in eye can be carried out by
using laser light that passes straight through
cornea at front of eye but is absorbed by retina
at back
· Refraction and total internal reflection…read more

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