Physics Unit 3

What are they?

Used to form images of bones on photgraphic films to check for fractures or dental problems.

Properties?

• They affect a photographic film in the same way as light
• They are absorbed by bone and metal
• They are transmitted by healthy tissue

Positive: X-rays and be used for therapy and can treat cancerous tumours that are near the body's surface.

Negative: Can cause ionisation and can damage living tissue.

Workers wear film badges and use lead screens to protect them from the x-rays.

Charge-coupled devices (CCD's) can be used to from electronic images of x-rays. 

CT Scanners use x-rays to produce digital images of a cross-section through the body

Human frequency boundaries: 20Hz - 20,000Hz

Above 20,000Hz is an ultrasound wave

Eletronic systems are used to produce ultrasound waves. When a wave meets a boundary between to different materials, a part of the wave is reflected. The reflected wave travels back to a detector.

THE TIME TAKEN TO TRAVEL BACK TO THE DETECTOR AND BE USED TO CALCULATE HOW FAR AWAY THE BOUNDARY IS.

The distance travelled by an ultrasound pulse can be calculated using:

s = v x t

• s is distance travelled in metres, m
• v is the speed of an ultrasound wave in metres per second, m/s
• t is the time taken in seconds, s

Ultrasounds are non-ionising, and is safer to use than x-rays.

Can be used to scan babies, can be used for therapy and can be used on soft tissues, e.g the eye.