P3 1 - Medical applications of physics
- 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)
- Refraction of light
- 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.
- The structure of the eye
- X-rays
- 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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