P3

P3

1. Medical applications of physics

   • X rays
     • X rays are used to make CT scans and to destroy tumours at or near the body surface
     • X rays can damage living tissue that they pass through
     • X rays are absorbed more by bones and teeth than by soft tissue
     • CT scans show the boundries between different types of soft tissue
   • Ultrasound
     • Ultrasound waves are sound waves above 20000Hz
     • Ultrasound is used for scanning and the destruction of kidney stones
     • Ultrasound is partially reflected at a boundry between types oftissue
     • Safer than X rays
   • Refractive index
     • Refractive index is a measure of how much a substance can refract a light ray
     • Refractive index = sin angle of incidence / sin angle of refraction
   • Endoscope
     • The critical angle is the angle of incidence of a light ray in a transparent substance that causes refraction along the boundry
     • Total internal reflection happens when the angle of incidence is greater than the critical angle
     • An endoscope is used to directly see inside the body
   • Lenses
     • A convex lens focuses parallel rays to the principal focus
     • A concave lens makes parallel rays spread as if they came from the principal focus
     • A real image is formed by the convex lens if the object is further away than the principal focus
     • A virtual image id formed by the concave lens and if the object is closer than the principal focus from a convex lens
   • The eye
     • Light is focused on the retina by the cornea and the lens
     • The normal human eye has a range of 25cm to infinity
     • Short sighted people can only see near objects clearly

2. Using magnetic feilds to make things work

   • Elecromagnets
   • The motor effect
   • Electromagnetic induction
   • Transformers
   • Case study

3. Using physics to make thingss work

   • Moments
     • A moment is the turning force of an object
     • To increase the moment, increase the force or increase the distance from the pivot
   • Center of mass
     • The center of mass of an object is the point where the mass may be thought to be concentrated
     • When an object is suspended at equilibrium, the center of mass is directly below the point of suspension
     • The center of mass of a symetrical object is along it line of symmetry
   • Moments in balance
     • For an object in equilibrium, the anticlockwise moment and the clockwise moments are equal
   • Stability
     • A wider base increases stability
     • Lower center of mass increases stability
   • Hydraulics
   • Circular motions
   • Pendulums