Medical Physics Flashcards
why do doctors carry X-ray counters
X-rays are ionising and can kill healthy cells/cause damage to DNA/damage cells/ cause cancer
4 examples of medicinal uses of X-rays
- imaging bones
- imaging dental problems
- imaging the body
- killing cancer cells
describe ultrasound
a longitudinal wave above 20,000Hz which is way beyond our upper range of human hearing
how are images formed using ultrasound
waves are partially reflected when they meet a boundary between two substances. the time taken for the echo gives the distance of the boundary. reflected waves are collected and processed into an image by a computer
what is refraction
the bending of light moving from one substance(medium) to another
what is the name of the point which a convex lens makes light rays meet
the focal point
why is an image formed from a lens virtual
the real light rays do not meet to make the image, virtual light rays meet instead
why are some people short sighted
their eyeball is too long or the lens is unable to focus light rays on the retina
why are some people long sighted
their eyeball is too short or the lens can not focus light rays onto the retina
give the near point and far point of our vision
near point-20cm
far point-infinity
which two parts of the eye refract light before it arrives at the retina
the lens and the cornea
which part of the eye changes the shape of the lens to focus close by and far away objects
ciliary muscles
how can a lens be made thinner and flatter but still have the power needed to refract correctly
lens must have a higher refractive index
2 factors affecting power of a lens
the refractive index
thickness of the lens
what is an X-ray
a very high frequency electromagnetic wave
what is the distance from a lens to the principle focus or focal point called
the focal length
what does the power of a lens tell you
how much the lens bends light rays
3 things that affect a lenses power
thickness
curvature
refractive index
what type of lens is found in a magnifying glass
a convex lens- or converging lens
the nature of an image is described in three ways
- virtual or real
- inverted or upright
- magnified x?
why does the shape of the lens in the eye need to be changed
to allow light rays to focus on the retina from objects close by (thick lens) and far away (thinner lens)
what happens to a light Ray in an endoscope
light is totally internally refracted because it reflects from the optical fibre of an angle larger than the critical angle
medical usage of a laser
an energy source used for cutting skin tissue,burning cells and sealing blood vessels
why does light totally internally refract in an optical fibre
the light hits the edge of the fibre at an angle bigger than the critical angle and reflects rather than refracts
