Physics Revision

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  • Created by: Théa
  • Created on: 14-05-13 17:35

What are X-rays?

-X-rays are part of the electromagnetic spectrum

-Very short wavelength (about the width of an atom)

-Can cause ionisation (knock off electrons from cells)

-Ionisation of atoms in DNA can lead to cancer

-X-rays can be used to treat cancer

-Can affect photographic film in the same way light does

-Can be absorbed by metal and bone

-Can be therefore used to diagnose broken bones

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Medical Uses of X-rays

-Diagnosis of chest conditions (e.g. Pneumonia)

-Detection of foreign objects

-Diagnose fractures

-Diagnose dislocations

-Diagnosis of bone or joint conditions (e.g. Arthritis)

-Surgical tool

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CT Scans

-Can show a person through 360 degrees

-Connected to charge-coupled device (CCD) which converts X-rays into light, to produce a 3D digital image 

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CT Scanner vs. X-ray Machine

CT Scanner:

-3D image

-More expensive

-Distinguish between hard and soft tissue

-Higher dose of X-rays

X-ray Machine:

-Lower dose of X-rays

-2D image


-Cannot distinguish between hard or soft tissue, only bones

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-Such a high frequency, humans cannot hear it. The human hearing range is 20Hz to 20,000Hz

-Speed of sound = wavelength x frequency

-Longitudinal waves (wave direction is same as wave motion, like a slinky, so it moves back and forth)

-Can be refracted, reflected and diffracted

-Requires a medium to travel through

-Speed of sound is affected by the medium. The higher the density, the higher the speed, as there are more particles.

-The shorter the wavelength of the wave on the oscilloscope, the higher the pitch and the longer the wavelength, the lower the pitch.

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Uses of Ultrasound

-Scanning unborn babies

-Scanning the heart

-Finding and treating kidney stones

-Communication between animals

-Navigation in boats or submarines (SONAR)

Calculating distance using ultrasound:

- Distance = speed x time/2 

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Ultrasound Scans And Kidney Stones

Ultrasound Scans:

-The wave is partially reflected when it meets a boundary between two different media (e.g. muscle, bone, liquid, fat, etc.) These reflections are collected and interpreted as a picture.

-Use a frequency of between 2MHz and 20MHz 

Kidney Stones:

-Ultrasound can also be used to treat kidney stones

-A high powered ultrasound is used for this

-Stones vibrate until they break apart and are easily passed out of the body via the urethra

-Advantageous as you do not have to have surgery and it is pain-free.

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Advantages and Disadvantages of Ultrasound


-Non-invasive (no surgery)

-'Real time' video

-Image is available immediately


-Considered risk-free, as it doesn't damage cells


-Images from deeper into the body result in progressively poorer resolution

-Relies on expertise of sonographer

-After 18 weeks of pregnancy, scans aren't to show anything but major problems with the baby, so smaller, more minor problems are not always detected.

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Ultrasound vs. X-rays


-Uses high frequecy sound waves

-Reflects off different tissues in the body and so can show soft and hard tissue and liquid

-The result is a 'real time' video

-Considered safe, as it uses non-ionising waves


-Uses high frequency electomagnetic waves

-It's blocked mainly be bone and is mainly used for looking at broken bones

-The result is an image developed later

-Too many X-rays could lead to cell damage as it is ionising radiation

-Image is made by a film on the other side of the object.

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