P3.1 Medical applications of physics Flashcards
What are x-rays part of?
The electromagnetic spectrum
What do x-rays have?
A very short wavelength
What do x-rays cause?
Ionisation
X-rays are absorbed by…
Metal and bone
X-rays are transmitted by…
Soft tissue
What can x-rays be used to diagnose and treat?
Some medical conditions, e.g. CT scans, bone fractures, dental problems and killing cancer cells
Do precautions need to be taken when x-ray machines and CT scanners are in use?
Yes
What is the range of human hearing?
20 Hz to 20 000 Hz
What can electronic systems be used to produce?
Ultrasound waves, which have a frequency higher than the upper limit of hearing for humans?
What happens to ultrasound waves when they meet a boundary between two mediums?
They are partially reflected
What can the time taken for reflections to reach a detector determine?
How far away the boundary is
What is the equation for distance between interfaces in various media?
s = v x t
What does the s stand for?
Distance
What does the v stand for?
Speed
What does the t stand for?
Time
Ultrasound waves can be used in…
Medicine, e.g. pre-natal scanning and the removal of kidney stones
What is refraction?
The change of direction of light as it passes from one medium to another
How does a lens form an image?
By refracting light
What happens in a convex or converging lens?
Parallel rays of light are brought to a focus at the principal focus
What is the distance from the lens to the principal focus called?
The focal length
What is the calculation for refractive index?
sin i
Refractive index = ———
sin r
What is the nature of an image defined by?
Its size relative to the object, whether it is upright or inverted relative to the object and whether it is real or virtual
What is the nature of an image produced by a converging lens at 2F?
Same size, inverted, real
What is the nature of an image produced by a converging lens further than 2F?
Diminished, inverted, real
What is the nature of an image produced by a converging lens close than 2F?
Magnified, upright, vitrual
What can a converging lens be used as?
A magnifying glass
What is the nature of an image produced by a concave lens?
Virtual, upright and diminished
How is magnification calculated?
image height
Magnification = ———————
object height
What is the function of the cornea in the eye?
Refracts light as it enters the eye
What is the function of the iris in the eye?
Controls how much light enters the pupil
What is the function of the pupil in the eye?
Allows light to pass through as it enters the eye
What is the function of the lens in the eye?
Refracts light and focuses it onto the retina. The amount of refraction can be adjusted by altering the thickness and curvature of the lens
What is the function of the ciliary muscles in the eye?
Adjust the shape of the lens to make it more or less curved, so as to increase or decrease the refraction of light
What is the function of the suspensory ligaments in the eye?
Slacken or stretch as the ciliary muscles contract or relax, to adjust the thickness and curvature of the lens
What is the function of the retina in the eye?
Contains the light receptors, which trigger electrical impulses to be sent to the brain when light is detected
What does correction of vision use?
Convex and concave lenses to produce an image on the retina
What is long-sightedness caused by?
The eyeball being too short or the eye lens being unable to focus
What is short-sightedness caused by?
The eye ball being too long or the eye lens being unable to focus
The eyes can focus on objects between the…
Near point and the far point
What is the near point?
Approximately 25 cm
What is the far point?
Infinity
What is the structure of the eye similar to?
A camera
What is the camera’s version of the retina?
The film or the CCD’s
What equation is the power of a lens given by?
1
P = —–
f
What does the p stand for?
Power in dioptres, D
What does the f stand for?
Focal length in metres, m
What is the power of a converging lens?
Positive
What is the power of a diverging lens?
Negative
What is the focal length of a lens determined by?
The refractive index of the material from which the lens is made and the curvature of the two surfaces of the lens
For a give focal length, the greater the refractive index…
The flatter the lens. This means that the lens can be manufactured thinner
What is the total internal reflection?
Beyond the critical angle, when all waves reflect back into the glass
What is the critical angle?
When the angle of incidence is equal to 90 degrees
What is the equation for total internal reflection and the critical angle?
1
refractive index = ———–
sin c
What does the c stand for?
Critical angle
What can visible light be sent along?
Optical fibres
What can a laser be used for?
Cutting cauterising and burning
An endoscope uses optical fibres, what is an endoscope used for?
Internal imaging
