Medical Applications of Physics

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X-rays are part of the electromagnetic spectrum.  They have a high frequency and a very short wavelength.  They affect a photographic film in the same way as light and 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.  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 that are made of soft tissue, such as the intestines, can be filled with a contrast medium that absorbs X-rays.  They can then be seen on an X-ray image.

However, X-rays cause ionisation and can damage living tissue when they pass through it. Workers should wear film badges and when possible use lead screens to shield them from the X-rays.  X-rays can also be used for therapy.  They can be used to treat cancerous tumours near the body surface.  So although X-rays can cause cancer, they can also be used to treat it.


The human ear can detect soundwaves with frequencies of between 20-20,000 Hz.  Sound waves of a higher frequency are called ultrasound waves.  Electronic systems can produce ultrasound waves.  When a wave meets a boundary between two different materials, part of the wave is reflected back.  The wave travels back through the medium to a detector.  The time it takes to reach the detector can be used to work out how far away the boundary is.  The results can be processed by a computer to produce an image.

The distance travelled by an ultrasound wave can be found using the equation:

s = vt, where s= the distance travelled in m, v= speed of the ultrasound wave in m/s and t is the time taken in s.

In the time between the transmitter sending out…


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