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1.1 X-Rays
· X-Rays are part of the electromagnetic spectrum.
· They have a high frequency and a short wavelength.
· Properties of X-rays
· They affect a photographic film in the same way as light
· They are absorbed by metal and bone
· They are transmitted by healthy tissue
· X-Rays are used to form images of bones on photographic
film to check for fractures and dental problems.
· X-Rays can be used to diagnose and treat some medical
conditions e.g killing cancer cells, detecting bone fractures
· X-Rays may also be used for therapy. They can be used to
treat cancerous tumours at or near the body surface.…read more

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Precautions should be taken when X-Rays and CT Scanners are in use
·X-Rays cause ionisation and can damage living tissue when they pass
through it. The precautions that should be taken are:
·Workers should wear film bandages
·If possible use lead screens to shield workers from X-rays
·Charge- coupled devices(CCDs) can be used to form electronic images
of X-rays. CT scanners use X-rays to produce digital images of a cross-
section through the body. Some body organs made of soft tissue, such
as the intestines, can be filled with a contrast medium that absorbs X-
rays so that they can be seen on an X-ray image.…read more

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1.2 Ultrasound
· The human ear can detect sound waves with a frequencies between 20Hz
and 20 000Hz. Sound waves with a higher frequency than this are called
ultrasound waves.
· Electronic systems can be used to produce ultrasound waves.
· When a wave meets a boundary between two different materials, part of
the wave is reflected. The wave travels back through the material to the
detector. The time it takes to reach the detector can be used to calculate
how far away the boundary is. The results may be processed by the
computer to give an image.
· The distance travelled by an ultrasound pulse can be calculated using the
equation: s = v x t , where s is the distance travelled in metres(m), v is the
speed of the ultrasound wave in metres per second(m/s) and t is the time
taken in seconds(s).
· In the time between a transmitter sending out a pulse of ultra sound and it
returning to a detector, it has travelled from the transmitter to a boundary
and back, i.e twice the distance to the boundary…read more

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Ultra sound can be used in medicine for scanning
·It is non-ionising so is safer to use than X-rays
·It can be used for scanning unborn babies and soft tissue
such as the eye.
·Ultrasound may also be used in therapy, for example to
shatter kidney stones into small pieces.…read more

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1.3 Refractive Index
· Refraction is the change of direction of
light as it passes from medium to another.
· A lens forms an image by refracting light.
· Refraction takes place because waves
change speed when they cross a boundary.
The change in speed of the waves causes a
change in direction, unless the waves are
travelling along a normal.
· A light ray will refract when it crosses from
air into glass. It is refracted towards the
normal.
· The refractive index of a substance is a
measure of how much the substance can
refract a light ray.
· The refractive index is given by the
equation: n=Sin i/ Sin r, where n is the
refractive index of a substance, sin i is the
sine of the angle of incidence and sin r is
the sine of the angle of refraction.…read more

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