P3.1 Medicle Physics Flashcards
Proportions of x rays?
Short wavelength
Very ionising
What length are x-rays?
10^-10m
How does an x ray work?
It’s absorbed by more dense materials like bone and metal but is transmitted through soft tissue creating an imagine
Uses of x rays?
Diagnosis
Treatment
Plan treatment
How are x rays made?
An accelerating electron hits atoms in a heavy metal target which emits them
What precautions need to be taken with x rays?
DES
What are CT scans?
X rays of slices of the human torso at different angles
How do CT scanners have a high contrast?
Removes scattered rays and rays that aren’t absorbed
Why are CT’s less dangerous?
Only hit one place once
Why is an x ray machine covered in lead?
So they only go in one direction
How do CT scanners have a high resolution?
Smaller wavelength
Narrow beam
CCD not a film
What type of waves are ultrasound waves?
Longitudinal waves
What frequency are ultrasound waves?
Above hearing range
20-20000Hz
What wave length do ultrasound waves have?
1/10mm to 1mm in soft tissue
How does ultra sound work?
When waves pass through a different media they change speed
Some are reflected, transmitted or absorbed
They time how long it takes for the reflected rays the come back and create an image with them
How can ultra sound be used?
Look at babies
Break up kidney stones
What’s good about the resolution of ultra sound?
High without compromising strength of reflected signal
Which way to rays go from air to glass?
Towards the normal
How do lens form an image?
Refracting light
How do you find the refracted angles?
Sin I/ n x Sin r
The larger the refractive index, the _______ change in direction
Larger
Where do the rays go on a converging diagram?
Through the centre
Straight to the line then down to the F
Through the first F to the line then straight
For a object behind the focal point what are the properties of the image?
Inverted
Virtual
Magnified
What are the properties for an object in front of the focal point in a converging lens?
Magnified
Real
Upright
Where are the rays on a diverging rays diagram?
Through the centre
Straight across then up from the left focal point
Down to the right focal point then straight from the centre line
Properties of an image through a diverging lens?
Virtual
Diminished
Upright
What is a real image?
Light rays meet
How do you find magnification?
Height of image/ height of object
What does a lens do?
Focus’ light into the retina
What does the pupil do?
Takes light in so the eye can focus
What does the cornea do?
Main refractive power
Converged light to an image
What does the iris do?
Controls the amount of light entering the eye
What does the ciliary muscle do?
Controls accommodation
What does the suspensory ligament do?
Holds the lens in place
What does the retina do?
Contains light receptors
Cones for colour
Rods for dim light and black and white
What is adult vision?
25cm to infinity
What’s accommodation?
How the eye focus’ of objects at different distances
For an object that’s near what happens in the eye?
Ciliary muscle contracts
Suspensory ligament slacks
Muscle tension is low
Lens is fat
For an object that far away what is the eye like?
Ciliary muscle relaxes
Suspensory ligament stretches
Muscle tension is high
Lens is thin
How do you find the power of a lens?
Power = 1/ focal length
How is focal length determined?
Refractive index
Curvature of material
For a given focal length, the greater the refractive index, the _____ the lens?
Flatter
If your short sighted whats wrong?
Too much refraction
Eye too long
If your long sighted what’s wrong?
Eye too short
Not enough refraction
For short sighted people what lens are in glasses?
Diverging
For long sighted people what lens are in glasses?
Converging
What’s accommodation on a camera?
Lens moving in and out
What’s the retina in a camera?
Photographic film or CCD
What’s total internal refraction?
Angle going in is greater than the critical angle
More to less dense
How do you find the critical angle?
N=1/sin c
What are the uses of total internal refraction?
Binoculars
Optical fibres
Endoscopy ( first bundle are incoherent but second bundle are in order to form an image)
What 4 properties of laser are different to light?
Higher intensity
One frequency (monochromatic)
Beam is columated
Light emitted is coherent
What precautions need to be taken with lasers?
In a lab
Dark safety goggles
Work below eye level
No reflective surfaces
Uses of lasers?
Cutting things with no drag so it’s more precise
Heat sealing
Laser eye surgery to reshape the cornea
