# P3.1 MEDICAL APPLICATIONS OF PHYSICS

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• Created by: Ellie
• Created on: 01-04-13 18:01

## P3.1.1 X-RAYS

a) X-rays are part of the electromagnetic spectrum. They have a very short wavelength and cause ionisation.

b) X-rays can be used to diagnose and treat some medical conditions.

c) Precautions to be taken when X-ray machines and CT scanners are in use.

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## P3.1.2 ULTRASOUND

a) Electronic systems can be used to produce ultrasound waves, which have a frequency higher than the upper limit of hearing for humans.

b) Ultrasound waves 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.

c) Calculation of the distance between interfaces in various media

s=vxt

(s is distance in metres, v is speed in metres per second, t is time in seconds)

d) Ultrasound waves can be used in machines.

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## P3.1.3 LENSES

a) Refraction is the change of direction of light as it passes from one medium to another.

b) A lens forms an image by refracting light.

c) In a convex or converging lens, parallel rays of light are brought to a focu at the principle focus. The distance from the lens to the principal focus is called the focal length

refractive index=sin i(angle of incidence)/sin r(angle of refraction)

d) The nature of an image is defined by its size relative to the object, whether it is upright or inverted relative to the object and whether it is real or virtual

e) The nature of the image produced by a coverging lens for an object placed at different distances from the lens. ]

f) The use of a coverging lens as a magnifying glass.

g) The nature of the image produced by a concave or diverging lens.

h) The construction of ray diagrams to show the formation of images by converging and diverging lenses.

i) The magnification produced by a lens is calculated using the equation:

magnification=image height/object height

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## P3.1.4 THE EYE

a) The structure of the eye. The structure of the eye is limited to: retina, lens, cornea, pupil/iris, ciliary muscle and suspensory ligaments.

b) Correction of vision using convex and concave lenses to produce an image on the retina: LONG SIGHT caused by the eyeball being too short, or the eye lens being unable to foucs, SHORT SIGHT caused by the eyeball being too long, or the eye lens being unable to focus.

c) Range of vision. The eye can focus on objects between the near point and the far point.

d) Comparison between the structure of the eye and the camera.

e) The power of a lens is given by:

P=1/f

(P is power in dioptres, f is focal length in metres)

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## P3.1.5 OTHER APPLICATIONS USING LIGHT

a) Total internal reflection and critical angle:

refractive index=1/sin c

(c is the critical angle)

b) Visible light can be sent along optical fibres.

c) The laser as an energy source for cutting, cauterising and burning.

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