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Physics > P3 topic 1 > Flashcards

P3 topic 1 Flashcards

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0
Q

Pupil

A

The hole in the centre of the iris which allows light into the eye

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1
Q

Cornea

A

The curved surface at the front of the eye that refracts light towards the lens

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2
Q

Iris

A

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)

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3
Q

Lens

A

The part behind the iris which focuses the light onto the retina

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4
Q

Ciliary muscles

A

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.

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5
Q

Retina

A

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.

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6
Q

what happens when light travels from a more optically dense material to a less optic dense material?

A

it is refracted and reflected at the boundary

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7
Q

what happens when the angle of incidence equals the critical angle?

A

some light is refracted at 90 degrees to the normal (ie it goes along the boundary) and some light is internally reflected

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8
Q

total internal reflection

A

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

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9
Q

critical angle

A

the angle of incidence in a denser medium that gives an angle of refraction equal to 90 degrees

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10
Q

what does the critical angle depend on?

A

the type of material

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11
Q

optical fibres

A

thin, flexible rods of transparent material such as glass for transmitting light from one end to another

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12
Q

how is light transmitted along optical fibres?

A

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

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13
Q

what are optical fibres used for?

A

transmitting high-speed signals in broadband networks and computers

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14
Q

endoscope

A

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

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15
Q

how many bundles of optical fibres does an endoscope use?

A

2- one to illuminate the inside of the patient and one to reflect the image back to an eyepiece or camera

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16
Q

how is electricity generated and received?

A

using piezoelectric transducers

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17
Q

what frequency of ultrasound is used to form images of the in insides of our bodies in hospitals?

A

1.5 mHz

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18
Q

what happens the higher the frequency of the ultrasound used to form images?

A

the shorter the wavelength, and then smaller the detail of the image can be

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19
Q

how can a 3D image be created with ultrasound?

A

by linking it to computers

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20
Q

why are ultrasound scans safer than x-rays?

A

ultrasound is a non-ionising radiation

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21
Q

what can ultrasound scans be used to diagnose?

A

cysts, tumours, blocked arteries, kidney stones, foetal abnormalities

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22
Q

what will happen to ultrasound inside our bodies?

A

it will be reflected and refracted at the boundaries between different types of tissue

23
Q

how is ultrasound used to remove kidney and bladder stones?

A

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

24
Q

what are kidney and bladder stones?

A

hard mineral deposits which can cause blockages and severe pain- they can be as large as 1cm in diameter

25
Q

how can ultrasound be used for physiotherapy?

A

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

26
Q

what are the risks of using ultrasound?

A

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

27
Q

what type of ultrasound do medical uses always stick to?

A

low-intensity

28
Q

ultrasound

A

very high frequency sound waves which cannot be heard by the human ear- the frequency is greater than 20 kHz

29
Q

radiation

A

any form of energy which can travel through space as a wave or a particle

30
Q

ionising radiation

A

some radiations ionise the atoms of the material they pass through- these radiations are known as ionising radiations

31
Q

non-ionising radiations

A

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

32
Q

what do ionising radiations include?

A

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

33
Q

how does radiation travel away from the source?

A

in all directions

34
Q

intensity of radiation

A

power of the radiation per unit area and it has the unit Watts per metre squared (W/m squared)

35
Q

what happens to the intensity if radiation at a point a distance away from a source?

A

decreases with distance from the source; depends on the material from the radiation is travelling through

36
Q

what can travel in a vacuum?

A

all EM radiation, but sound waves can’t

37
Q

why is radiation spread evenly over the surface area of a sphere?

A

radiation usually spreads out in all directions from a source

38
Q

what is intensity inversely proportional to?

A

the area and the square of the distance

39
Q

converging lens

A

bends the light towards a focal point- it’s fatter in the middle and thinner at the edges

40
Q

diverging lens

A

bends the light away from a focal point- it’s thicker at the edges and thinner in the middle

41
Q

focal length

A

the distance between the principle focus and the centre of the lens

42
Q

what happens the fatter the converging lens?

A

the shorter its focal length

43
Q

optical power

A

the reciprocal of the focal length

44
Q

unit of power of a lens

A

dioptre

45
Q

what happens the greater the power of a lens?

A

the more it refracts or bends the light rays- a fatter converging lens will be more powerful than a thinner one

46
Q

what does a diverging lens have by convention?

A

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

47
Q

what’s the the total power of a combined lens system?

A

the sum of the powers of tie individual lenses

48
Q

when are real images formed?

A

when the rays actually cross in a rat diagram

49
Q

long sight

A

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

50
Q

how can long sightedness be caused?

A

by the eyeball being too short; cornea not being curved enough; lens not being fat enough

51
Q

how can long sightedness be corrected?

A

by wearing converging lenses

52
Q

short sight

A

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

53
Q

how can short sightedness be caused?

A

the eyeball being too long; the cornea being too curved; the lens being unable to become thin enough

54
Q

how can short sightedness be corrected?

A

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

55
Q

laser eye surgery

A

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

56
Q

what does most laser eye surgery do?

A

it changes the shape of the cornea which can correct mile eye defects

Physics (15 decks)

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