Medical Applications

Medical Applications

1. X-rays

   • Very short wavelength, high frequency
   • Causes ionisation --> Damage living tissue
     • Workers wear lead aprons and film badges
       • Badges shows exposure to radiation
   • Can be used to diagnose and treat medical conditions
     • To diagnose
       • CT Scanner
         • Gives photograph of the soft and hard TISSUE
           • DOES NOT PASS THROUGH SOFT TISSUE
     • To treat
       • Radiation treatment for cancer
         • The x-rays kill the cancer cells
           • A beam of x-rays is focused on the tumour and destroys it
             • Can burn skin --> Given cream
   • Gives photograph of the BONES
     • E.g. Dental x-rays, Bone fractures
       • They PASS THROUGH SOFT TISSUE and are absorbed by bones and metal

2. Ultrasound

   • A sound with a higher frequency than we can hear (we can hear 20Hz - 20,000Hz)
   • Ultrasound get partially reflected at a boundary between media (substances)
     • When the ultrasound wave travels from one medium to another, some is reflected and some is refracted
       • Partial reflection
         • The time it takes for the reflection to reach detector --> measures how far away the boundary is
           • Ultrasound image (photo)
           • Oscilloscope trace
             • Time between reflected pulses measured on the screen (t)
               • The distance between the boundaries can be measured (s)
                 • You need to know the speed of sound in the medium (v)
                   • s = v x t
                     • Reflected pulses have travelled there and back (twice the distance between boundaries) so s is halved
   • A sound wave
   • Non-ionising and very safe
     • Used on pregnant women to get image of baby
     • Remove kidney stones

3. Lenses

   • Concave
     • Diverging lens
       • Light rays spread out (diverge)
         • Principal focus (F) is point behind the lens where the rays all appear to come from
     • Curves inwards
   • Refraction is the change of direction of light as it passes from one medium to another
     • Refractive index (n) = sin i/sin r
       • A lens forms an image by refracting light
         • my mums poop
       • RI of a transparent material
         • The angle of refraction depends on the refractive index of the material
   • Convex
     • Converging lens
       • Light rays move together (converge)
         • Light rays meet at principal focus (F)
     • Curves outwards
   • The centre of the lens is called the axis
     • Focal length is the distance from the centre of the lens to the principal focus
       • Principal focus = along axis
       • P = 1 / f
   • Virtual image - upright
     • Image is formed behind the object
       • The image is magnified - lens acts as a magnifying glass
         • To describe image:
           • If its real or virtual
           • If its upright or inverted
           • How big it is compared to object
         • Magnification = image height / object height
   • Real image - inverted
     • Where the light from an object converges to form an image on a screen