# Physics 3 - Physics in Medicine

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

## X-Rays

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

1 of 16

## Ultrasound

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

2 of 16

## Refraction

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

3 of 16

## Refractive index

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

4 of 16

## Images

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

5 of 16

## Converging Lense

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

6 of 16

## Diverging Lense

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

7 of 16

## Magnification

Magnification = image height/object height

8 of 16

## 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.

9 of 16

## Short-sight

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

10 of 16

## Long-sight

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

11 of 16

## Camera

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

12 of 16

## Powerful lenses

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

13 of 16

## TIR

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

14 of 16

## Optical fibres

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

15 of 16

## Lasers

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.

16 of 16