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Medical Imaging ­ X-rays
CCDs (charged coupled devices) are silicon chips
made up of millions of pixels that detect X-rays/light
and produce electronic signals to form high
resolution image. Used in digital cameras.
CT stands for Computerised axial Tomography ­ it's
used for planning complicated surgery.
For treating cancer X-rays are focused on the
tumour using a wide beam which is rotated round
the patient.…read more

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Medical Imaging - Ultrasound
Ultrasound can be used in industry to find cracks
in metal or to clean jewellery.
Ultrasound is partially reflected, partially
We use Distance = Speed x Time to find out the
distance between boundaries, but the result
must be halved as the ultrasound has gone there
and back.…read more

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The change of speed of a wave is what causes
refraction when it enters a new medium.
When a wave slows it bends towards the normal.
If a wave hits a boundary at 90º it will not change
When light hits a different medium some is reflected.
Refractive index of a medium is the ration of speed of
light in a vacuum to speed of light in that medium.…read more

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Magnification & Power
Magnified objects produce a virtual image. The object
Magnification = image height ÷ object height
A powerful lens has a short focal length because Power (in
dioptres) = 1 ÷ focal length (m).
Converging lens: power positive +
Diverging lens: power negative ­
The focal length is determined by the refractive index of
the lens material and the curvature of the lens material.…read more

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The Eye
Cornea and lens do most of the focusing
Iris and pupil sort out light intensity
Retina has light-sensitive cells which detect light
and sends a signal to the brain
A camera and eye produce real, inverted,
diminished images. The CCD in the camera is
the equivalent of the retina.…read more

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