Physics 3 - Physics in Medicine

  • Created by: Alice
  • Created on: 07-04-15 18:18


X-Rays are electromagnetic waves with a short wavelenth.
They are ionising, so potentially dangerous.

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Ultrasound waves are sound waves with a frequency above 20,000 Hz.
Ultrasound reflects off boundaries between materials.

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Refraction is the bending of light when it moves from one medium to another.
Lenses use refraction to form an image.

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Refractive index

Refractive index is a measure of the speed of light through a material compared with the speed of light in a vacuum.

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The nature of an image is determined by its distance from the lens, its size, its orientation, and wheter it is real or virtual.

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Converging Lense

The image produced by converging lenses is real and inverted, or virtual, upright and magnified.

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Diverging Lense

The image produced by diverging lenses is virtual, upright, and diminished.

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Magnification = image height/object height

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Human Eye

The human eye has a range of vision from 25cm to infinity.
Features of the eye:  retina; cornea; iris; pupil; ciliary muscles; suspensory ligaments.

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Short-sight is inability to focus on far away objects.
Corrected by diverging lenses.

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Long-sight is inability to focus on near objects.
Corrected by converging lenses.

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In a camera a converging lens focuses light onto photographic film or a charge-coupled device (CCD) to produce a real image.

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Powerful lenses

More powerful lenses have shorter focal lengths.
Lens power is measures in dioptres.
Power = 1/focal lenght.

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If the angle of light travelling from a denser medium towards a less dense medium exceeds the critical angle, total internal reflection (TIR) occurs.

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Optical fibres

Optical fibres channel light through total internal reflection, and are used for communication and in endoscopes.

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Laser beams remain very narrow even over long distances.
Their intensity means they can be used to cut, etch, or cauterise objects - including in laser eye surgery.

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