P3 1 - Medical applications of physics

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  • Created by: Natalia
  • Created on: 11-03-13 20:04
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  • P3 1 - Medical applications of physics
    • X-rays
      • Part of the electomagnetic spectrum.
      • Very short wavelength.
      • Cause ionisation.
      • They affect a photographic film in the same way as light.
      • Absorbed by metal and bone.
      • Transmitted by healthy tissue.
      • Their wavelength is of the same order of magnitude as light.
      • Can be used to diagnose and treat some medical conditions.
        • Using CT scans
        • Such as bone fractures and dental problems.
        • To kill cancer cells.
        • The use of charge-coupled devices (CCDs) allows images to be formed electronically.
      • Precautions must be taken when X-ray machines and CT scanners are in use.
    • Ultrasound
      • Can be produced by electronic systems.
      • 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.
      • 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.
        • Calculation of the distance between interfaces in various media: s = v X t  where 's is distance in metres, m'.     'v is speed in metres per second, m/s'.  't is time in seconds, s'.
      • Can be used in medicine.
        • Pre-natal scanning.
        • Removal of kidney stones.
    • Lenses
      • Refraction of light
        • Refraction is the change of direction of light as it passes from one medium to another.
        • A lens forms an image by refracting light.
        • Refractive index = (sin i) / (sin r). Where i is the angle of incidence and r is the angle of refraction.
      • Converging lenses
        • Thickest at the centre.
        • A converging lens can be used as a magnifying glass.
        • The image produced by the lens is real (on the other side of the lens), inverted and smaller (for distant objects) or magnified.
      • Concave lenses
        • The image produced is virtual (on the same side as the object) and upright (not inverted).
      • The magnification caused by a lens can be calculated using the equation: magnification= (image height) / (object height)
    • The eye
      • The structure of the eye
        • The retina contains the light receptors.
        • The lens focuses right onto the retina and provides further refraction.
        • The cornea refracts light - it bends it as it enters the eye.
        • The iris controls how much light enters the pupil.
        • The pupil adjusts the light intensity.
        • The ciliary muscles control the shape of the eye lens. This allows light from objects at different distance to be brought into focus.
        • The suspensory ligaments hold the lens in position and alter its shape in conjunction with the ciliary muscles.
      • Correction of image to produce an image on the retina:
        • Long sighted, caused by the eyeball being too short or the lens being unable to focus.
        • Short sighted, caused by the eyeball being too long, or the lens being unable to focus.
  • Calculation of the distance between interfaces in various media: s = v X t  where 's is distance in metres, m'.     'v is speed in metres per second, m/s'.  't is time in seconds, s'.
  • A lens forms an image by refracting light.

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