P3 topic 1 Flashcards
Pupil
The hole in the centre of the iris which allows light into the eye
Cornea
The curved surface at the front of the eye that refracts light towards the lens
Iris
The coloured part of the eye which is the muscle that changes the size of the pupil (and therefore the amount of light entering it)
Lens
The part behind the iris which focuses the light onto the retina
Ciliary muscles
The muscles to change the shape of the lens. A thin lens is needed to view distant objects and a fatter lens is needed for objects closer up. This is called accommodation.
Retina
The inside surface at the back of the eye which contains many light sensitive cells that send messages along the optic nerve to the brain.
what happens when light travels from a more optically dense material to a less optic dense material?
it is refracted and reflected at the boundary
what happens when the angle of incidence equals the critical angle?
some light is refracted at 90 degrees to the normal (ie it goes along the boundary) and some light is internally reflected
total internal reflection
a phenomenon where 100% of the light is reflected back into a material, where the ray hits the boundary at an angle greater than the critical angle
critical angle
the angle of incidence in a denser medium that gives an angle of refraction equal to 90 degrees
what does the critical angle depend on?
the type of material
optical fibres
thin, flexible rods of transparent material such as glass for transmitting light from one end to another
how is light transmitted along optical fibres?
by being totally internally reflected all the way along- it can’t escape as it always hits the boundary at an angle greater than the critical angle
what are optical fibres used for?
transmitting high-speed signals in broadband networks and computers
endoscope
a medical instrument used to see inside the human body- it used optical fibres and can be equipped with other surgical instruments to carry out keyhole surgery
how many bundles of optical fibres does an endoscope use?
2- one to illuminate the inside of the patient and one to reflect the image back to an eyepiece or camera
how is electricity generated and received?
using piezoelectric transducers
what frequency of ultrasound is used to form images of the in insides of our bodies in hospitals?
1.5 mHz
what happens the higher the frequency of the ultrasound used to form images?
the shorter the wavelength, and then smaller the detail of the image can be
how can a 3D image be created with ultrasound?
by linking it to computers
why are ultrasound scans safer than x-rays?
ultrasound is a non-ionising radiation
what can ultrasound scans be used to diagnose?
cysts, tumours, blocked arteries, kidney stones, foetal abnormalities
what will happen to ultrasound inside our bodies?
it will be reflected and refracted at the boundaries between different types of tissue
how is ultrasound used to remove kidney and bladder stones?
they can be destroyed using high frequency ultrasound- pulses of ultrasound waves are focused onto the stones and this high frequency vibration causes the stones to break up into small fragments which can easily pass out of the body naturally in the urine
what are kidney and bladder stones?
hard mineral deposits which can cause blockages and severe pain- they can be as large as 1cm in diameter
how can ultrasound be used for physiotherapy?
high frequency ultrasound in human tissue causes fluctuations in pressure, which leads to heating in the body- in physiotherapy, ultrasound can be used to produce localised heating in damaged muscle tissue, which increased the rate of healing
what are the risks of using ultrasound?
very intense ultrasound can cause dissolved gases (oxygen and carbon dioxide) to form tiny bubbles in the blood- when the bubbles collapse, they can damage tissue in the body
what type of ultrasound do medical uses always stick to?
low-intensity
ultrasound
very high frequency sound waves which cannot be heard by the human ear- the frequency is greater than 20 kHz
radiation
any form of energy which can travel through space as a wave or a particle
ionising radiation
some radiations ionise the atoms of the material they pass through- these radiations are known as ionising radiations
non-ionising radiations
radio waves from a transmitter; microwaves from a mobile phone; infrared radiation from a heater; light from a lamp or laser; ultrasound radiation used in hospitals for ultrasound scans
what do ionising radiations include?
ultraviolet radiation from the sun; x-rays from an x-ray machine; gamma radiation from a radioactive isotope; alpha or beta particles from radioactive isotopes
how does radiation travel away from the source?
in all directions
intensity of radiation
power of the radiation per unit area and it has the unit Watts per metre squared (W/m squared)
what happens to the intensity if radiation at a point a distance away from a source?
decreases with distance from the source; depends on the material from the radiation is travelling through
what can travel in a vacuum?
all EM radiation, but sound waves can’t
why is radiation spread evenly over the surface area of a sphere?
radiation usually spreads out in all directions from a source
what is intensity inversely proportional to?
the area and the square of the distance
converging lens
bends the light towards a focal point- it’s fatter in the middle and thinner at the edges
diverging lens
bends the light away from a focal point- it’s thicker at the edges and thinner in the middle
focal length
the distance between the principle focus and the centre of the lens
what happens the fatter the converging lens?
the shorter its focal length
optical power
the reciprocal of the focal length
unit of power of a lens
dioptre
what happens the greater the power of a lens?
the more it refracts or bends the light rays- a fatter converging lens will be more powerful than a thinner one
what does a diverging lens have by convention?
a diverging lens has a virtual principal focus (the rays of light don’t actually meet at the principal focus, they appear to be coming from it), so by convention it has a negative focal length and a negative power
what’s the the total power of a combined lens system?
the sum of the powers of tie individual lenses
when are real images formed?
when the rays actually cross in a rat diagram
long sight
long-sighted people can see distant objects clearly but cannot focus on close objects; their near point for a long sighted person will be greater than 25cm and the image of a closer object will be formed behind the retina
how can long sightedness be caused?
by the eyeball being too short; cornea not being curved enough; lens not being fat enough
how can long sightedness be corrected?
by wearing converging lenses
short sight
they can see close objects, but cannot focus on distant objects; the far point for short sighted people is less than infinity and the image of more distant objects will be in front of the retina
how can short sightedness be caused?
the eyeball being too long; the cornea being too curved; the lens being unable to become thin enough
how can short sightedness be corrected?
may be corrected by wearing diverging lenses; corrective lenses may be worn as spectacles or contact lenses but the power of the lenses will not be the same, as the lenses are worn at different distances from the eyes
laser eye surgery
can be used as a permanent by alternative to wearing glasses or contact lenses- laser eye surgery can be painful for a few days and like with any surgical procedure there is a possibility of infection
what does most laser eye surgery do?
it changes the shape of the cornea which can correct mile eye defects
