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P3 Revision
Medical
Why are X-rays dangerous?
They are ionising
Medical
Aside form X-ray pictures how else are X-rays
used medically?
Used to destroy
cancerous tumours
Medical
What happens to the X-rays when a ‘picture’ of
a broken bone is taken?
Bones and teeth absorb the X-rays
whilst soft tissue allows it to pass
through
Medical
What is the range of human
hearing?
20 – 20 000 Hz
Medical
What happens to the ultrasound wave at the
boundary of each tissue boundary?
It is partially reflected
Medical
What is the name of the device that produces
and receives the ultrasound waves?
Transducer
Medical
What are the advantages of ultrasound over X-rays?
Non-ionising and can be used to
scan organs and soft tissues
Medical
How do you calculate the distance travelled by
an ultrasound wave?
Distance = speed x time
Medical
How do you calculate the distance between the
transducer and the tissue boundary?
Distance = speed x time
2
Medical
Aside from scanning how can ultrasound be
used medically
Ultrasound waves can be used to
break up a kidney stone
Medical
Where does refraction occur?
At the boundary of air and a
transparent substance (glass or
water)
Medical
What is Snell’s Law
Refractive Index = sini /sin r
Medical
What is the refractive index?
A measure of how much a
substance can refract a light ray.
Increasing
Refractive Index
Medical
Speed away… slow toward what?
The normal
Medical
When does total internal reflection occur?
When angle of incidence of a
light ray in a transparent
substance is greater than the
critical angle.
Medical
How does an endoscope work?
Two bundles of optical fibres,
one to carry the light the other
to carry light back to the
camera/eye. Light is totally
internally reflected.
Medical
What is the relationship between the critical and
gle and the refractive index?
Refractive index = 1/critical angle
Medical
What is the critical Angle ?
Angle of incidence of a light ray
in a transparent substance that
produces refraction along the
boundary.
Medical
Draw how light rays behave when they strike a
converging ( convex) lens
One ray through centre of lens the
other to the lens and through the
focal point.
Medical
Draw how light rays behave when they strike a
diverging ( concave) lens
One ray through centre of lens the
other to the lens and traced back
through the focal point.
Medical
What is the difference between a real image and
a virtual image?
Real images produced where real
light rays meet
Medical
Which three ways do we describe an image
Real/virtual, magnified/
diminished, upright/inverted
Medical
How do you calculate the magnification?
Image height / object height
Medical
What are the units for magnification?
There are none.
Medical
How is a camera like the eye
Both converging lenses, eye lens is
variable, camera lens fixed but changes
position, image formed on retina, camera
uses film, iris in eye and aperture for
control of light
Medical
Draw the eye and label as many structures as
you can
Cornea, lens, pupil, cliliary
muscles, retina, blind spot, optic
nerve, eye muscles
Medical
Draw how a short sighted eye sees
Medical
Draw how a long sighted eye sees
Medical
How do you calculate the power of a lens?
Power of a lens = 1/focal length
in metres
Medical
If a lens has a power with a positive value this
means it is which type of lens?
Converging ( convex)
Medical
If a lens has a power with a negative value this
means it is which type of lens?
Diverging ( concave)
Medical
What is the unit of power of a lens?
Dioptre
Medical
What is the range of human vision?
25cm (near point) and infinity (far
point)