P3. 1 Medical Applications of Physics

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P3.1 Medical Applications of Physics
Physics has many applications in the field of medicine. These include the uses of
Xrays and ultrasound for scanning, and of light for image formation with lenses
and endoscopes.
P3.1.1 XRays
Xrays are part of the electromagnetic spectrum. They have a very short wavelength and cause ionisation.
Properties of Xrays include:
they affect a photographic film in the same way as light
they are absorbed by metal and bone
they are transmitted by healthy tissue
their wavelength is of the same order of magnitude as the diameter of an atom.
Xrays can be used to diagnose and treat some medical conditions. (Examples include CT scans, bone
fractures, dental problems and killing cancer cells. The use of chargecoupled devices (CCDs) allows
images to be formed electronically). Precautions to be taken when Xray machines and CT scanners are in
use because radiation can cause cancer.
P3.1.2 Ultrasound
Electronic systems can be used to produce ultrasound waves, which have a frequency higher than the
upper limit of hearing for humans. The range of human hearing is about 20 Hz to 20 000
Hz.Ultrasound waves are partially reflected when they meet a boundary between two different media. The
time taken for the reflections to reach a detector can be used to determine how far away such a boundary
is. The greater the speed of a vehicle the greater the braking force needed to stop it in a certain distance.
Calculation of the distance between interfaces in various media: s= v x t
s is distance in metres, m
v is speed in metres per second, m/s
t is time in seconds, s
Ultrasound waves can be used in medicine. Examples include prenatal scanning and
the removal of kidney stones.
P3.1.3 Lenses
Refraction is the change of direction of light as it passes from one medium to another. A lens forms an
image by refracting light. In a convex or converging lens, parallel rays of light are brought to a focus at
the principal focus. The distance from the lens to the principal focus is called the focal length.
Refractive Index = Sin i/ Sin r (i =is the angle of incidence) (r = is the angle of
reflection) The nature of an image is defined by its size relative to the object, whether it is upright or
inverted relative to the object and whether it is real or virtual. The nature of the image produced by a
converging lens for an object placed at different distances from the lens. The nature of the image is
produced by a concave or diverging lens. The magnification produced by a lens is calculated
using the equation: Magnification = image height/object height
P3.1.4 The Eye
The structure of the eye is limited to:
pupil /iris
ciliary muscle

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P3.1 Medical Applications of Physics
suspensory ligaments.
Correction of vision using convex and concave lenses to produce an image on the retina:
Long sight, caused by the eyeball being too short, or the eye lens being unable to focus
Short sight is caused by the eyeball being too long, or the eye lens being unable to focus.
Range of vision: The eye can focus on objects between the near point and the far point.…read more


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