Medical Applications Of Physics Flashcards
What are the properties of X-rays
They affect a photographic film in the same way as light
They are absorbed by metal and bone
They are transmitted by healthy tissue
What are X-rays used for
To form images of bones on photographic film to check for fractures and dental problems
What do X-rays have
High frequency and a very short wavelength
What are charged coupled devices used for
Forming electronic images of X-rays
What do ct scanners do
Use X-rays to produce digital images of a cross section through the body
How cansoft tissue be seen on a X-ray machine
Some body organs made of soft tissue such as the intestines can be filled with a contrast medium that absorbs X-rays so they can be seen on n X-ray image
Why can X-rays damage living tissue
They are ionising
How can workers protect themselves from X-rays
Wear film badges
Use lead screens to shield themselves
What can X-rays be used to treat
They can be used to treat cancerous tumours or near the body’s surface
What is the range that a human ear can hear
20-20000 hz
What are ultrasound waves
Sound waves with a higher frequency than 20000 hz
How can electronic systems produce ultrasound waves
When a wave meets a boundary between two different materials part of the wave is reflected. The wave travels back through the material to a detector. The time it takes to reach the detector can be used to calculate how far away the boundary is. The results may be processed by a computer to give an image
In the time between sending out a pulse of ultrasound and it returning to a detector……….
It has travelled from the transmitter to a boundary and back, ie twice the distance to the boundary
Why are ultrasound Ray’s safer than X-rays
They are non ionising
How are ultrasounds used
Scanning unborn babies
Soft tissue such as the eye
Used in therapy eg to shatter kidney stones into small pieces
What is refraction
The change in direction of light as it passes from one transparent substance into another
Why does refraction take place
Waves change speed when they enter a boundary. The change in speed causes a change in direction
When does refraction not take place when crossing a boundary
When the wave travels along the normal
When a light Ray crosses from air into glasss……..
It is refracted towards the normal
What is the refracted index
Is a measure of how much the substance can refract a light Ray
Where are the angles I and r measured from
Between the Ray and the normal
What way will a light Ray refract when it crosses from glass to air
Away from the normal
WhAt is seen as a light Ray crosses from glass to air
A partially reflected Ray
What happens if the angle of incidence is increased
The angle of refraction increases until the refracted Ray emerges along the boundary
What is the angle of incidence also called when it is increased to the point where The angle of refraction increases until the refracted Ray emerges along the boundary
Critical angle
What happens if the angle of incidence goes beyond the critical angle
The light Ray undergoes total internal reflection
What happens when total internal reflection occurs
The angle of reflection is equal to the angle of incidence
What is an endoscope
A device used to look inside a patients body without cutting it open or when performing keyhole surgery
What does the endoscope contain and what are they
Optical fibres, very thin flexible glass fibres
How is visible light sent along optical fibres
By total internal reflection
What may be used as an energy source for endoscopy
Laser light
What can endoscopy procedures do
Cut, cauterise, burn
Why is the colour of light matched to the tissue in endoscopy
To produce maximum absorption
How does endoscopy eye surgery work
Using a laser light that passes straight through the cornea at the front of the eye but is absorbed by the retina at the back
What happens when parallel Ray’s of light pass through a converging convex lens
They are refracted so that they converge to a point
What is the principal focus point
The point where light rays parallel to the principal axis of a lens are focuses or in the case of a diverging lens, appear to diverge from
What is the focal length
The distance from the centre of the lens to the principal focus
Why is there a principal focus on either side of the lens
Because light can pass through the lens in either direction
When is a real image formed
If the object is further away from the lens than the principal focus
What is a real image
An image formed where light rays meet
What does the size of the real image depend on
The position of the object, the nearer the object to the lens the larger the image
When is a virtual image formed
If the object is further away from the lens than the principal focus
What is a virtual image
An image seen in a lens of mirror from which light rays appear to come after being refracted by the lens or reflected by the mirror
If the object is further away from the lens than the principal focus and a virtual image is created what happens
The image is magnified, the lens acts as a magnifying glass
How Is magnification calculated
Image heigh divided by object height
What happens when parallel light rays pass through a diverging concave lens what happens
They are refracted so that they diverge away from a point. This point is called the principal focus
What is the focal length
The distance from the centre of the lens to the principal focus
What is the image produced by diverging concave lenses always
Virtual
What is a Ray diagram
A diagram can be drawn to find the position and nature of an image formed by a lens
What is the principal axis
A straight one that passes along the normal at the centre of each lens surface
What are the 3 construction rays from a single point on the object used to locate the corresponding point on the image
A Ray parallel to the principal axis is refracted through the principal focus
A Ray through the centre of the lens travels straight on, without refraction
A Ray through the principal focus is refracted parallel to the principal axis
Is the image formed in a camera real or virtual?
A camera uses a converging lens to form a real image of an object on a film or an array of CCDs
What does light enter the eye through
Cornea
What do the cornea and lens work to do
Focus the light on to the retina
What does the iris adjust
The size of the pupil
Why does the iris adjust the size of the pupil
To control the amount of light entering the eye
What do the ciliary muscles do
They alter the thickness of the lens to control the fine focus ing of the eye
What are the ciliary muscles attached to the lens with
Suspension ligaments
What is the retina
The light sensitive cells around the inside of the eye
What is the blind spot
Region where the retina is not sensitive to light (no light sensitive cells present)
What does the optic nerve do
Carries nerve impulses from the retina to the brain
What is the iris
Coloured ring of muscle that controls the amount. Of light entering the eye
What is the cornea
transparent layer that protects the eye and helps to focus light onto the retina
What is the pupil
The central hole formed by the iris. Light enters the eye through the pupil
What is a near point
the nearest point to an eye at which an object can be seen in focus by the eye.
What is the near point of a normal human eye
25cm
What is a far point
the furthest point from an eye at which an object can be seen in focus by the eye
What is the far post. Of a normal human eye
Infinity
What is the human range of vision
25cm to infinity
What does it mean to be short sighted
A person who can see close objects clearly, but distant objects are blurred because the I corrected image is formed in front of the retina
What is short sighted ness caused by
The eyeball being too long or the eye lens being too powerful
How is short sight corrected
Diverging lenses
What does it mean to be long sighted
They can see distant objects clearly, but close objects are blurred because the I corrected image is formed behind the retina
What is long sighted ness caused by
The eyeball being too short or the eye lens being too weak
How is long sightedness corrected
Converging lenses
What is the focal length determined by
The refractive index of the material from which the lens is made
The curvature of the 2 surfaces of the lens
For a lens of a given focal length the greater the refractive index of the lens material,
The flatter and thinner the lens can be manufactured
