Unit 3 Flashcards
X-Rays are transmitted through healthy tissue, what are they absorbed by?
Denser materials like bones and metal
What can X-Rays be used for?
To see:
Bone fractures
Dental problems
How are X-Rays formed?
Electronically using charge-coupled devices (CCDs)
What are CCDs?
Silicon chip about the same size as a postage stamp, in which are divided up into a grid of identical pixels
What do CCDs produce?
They produce electronic signals which are used to form high resolution images
Define ‘CT’ scan
Computerised axial tomography
What does a CT scan do?
Creates a 3D image of the inside of the body
What does hight doses of X-Rays do?
Kill living cells
What X Ray is used to treat cancer?
Gamma radiation
How does the X-ray kill the cancer cell without the living cells being killed too?
The X-Rays have to be carefully focused at the right dosage to kill the cancer cells without damaging too many normal cells
How do they treat cancer?
1) the X-rays are focused on the tumour using a wide beam.
2) the beam is rotated round the patient with the tumour at the centre.
3) this minimised the exposer of the normal cells and changes of damaging the rest of the body.
What do radiographers have to wear for protection when doing a scan?
Wear a lead apron
Stand behind a lead screen or leave the room
What size is an X-Ray wavelength?
Roughly the same size as the diameter of an atom
What is done to protect the patient from the radiation?
A lead shield is put in place to protect the areas that aren’t being scanned
What is the range of a humans hearing?
20 Hz to 20 000 Hz
What is ultra sound?
Electrical oscillations of any frequency which is easily converted into mechanical vibrations to produce sound waves of a higher frequency than the upper limit of human hearing
Where do ultrasound waves get partially reflected?
At a boundary between media
How is ultrasound used in medicine?
Investigation blood flow
Heart problems
Check on fatal development
What causes refraction?
The waves change direction and speed
What are the 2 types of lens?
Converging
Diverging
What’s a converging lens?
A converging lens is convex (it bulges outwards) it causes parallel Rays of light to converge (move together)
What’s a diverging lens?
It’s concave (it caves inwards) it causes parallel Rays of light to diverge (spread out)
What’s the ‘axis’ of a lens?
The line passing through the middle
What’s the principal focus of a converging lens?
Where the light rays hitting the lens parallel to he axis all meet
What’s the principal focus of a diverging lens?
Where the rays hitting the lens parallel to the axis appear to come from - you can trace them back until they all appear to meet up behind the lens
What’s the principal focus of each side of the lens?
The distance from the centre of the lens to the principal focus is called the focal length
How is a ‘real image’ constructed?
Where the light from the object comes together to form an image on a ‘screen’ - like the image formed on an eyes retina
3 rules for refraction in a converging lens?
1) an incident Ray parallel to the axis refracts through the lens and passes through the principal focus on the other side
2) an incident Ray passes through the principal focus refracts through the lens and travels parallel to the axis
3) an incident Ray passing through the centre of the lens carries on in the same direction
The 3 rules for refraction in a diverging lens?
1) the incident Ray parallel to the axis refracts through the lens and travels in line with the principal focus
2) an incident Ray passing through the lens towards the principal focus refracts through the lens and travels parallel to the axis
3) an incident Ray passing through he centre of the lens carries on in the same direction
What uses a converging lens?
A magnifying glass
THE EYE
What is a cornea?
A transparent ‘window’ with a convex shape, and a high refractive index
THE EYE
What is the colourful part of the eye called and what is it controlled by?
The politic part is called the iris
It is made up of muscles that control the size of the pupil
What is a pupil?
A hole in the middle of the iris
What does the pupil do?
It controls the light intensity entering the eye
THE EYE
Why does the lens change shape?
To focus light from objects at varying distances
Where are images formed?
On the retina, which is covered in light sensitive cells
Whats the furthest distance the eye can focus on comfortably?
Infinity
What’s the shortest distance the eye can focus on comfortably?
Approx 25cm
THE EYE
Why does the lens change shape?
To focus light from objects at varying distances
Where are images formed?
On the retina, which is covered in light sensitive cells
Whats the furthest distance the eye can focus on comfortably?
Infinity
What’s the shortest distance the eye can focus on comfortably?
Approx 25cm
