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Physics > P3.1 > Flashcards

P3.1 Flashcards

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1
Q

Why is the handle for a door in the position that it is?

A

It’s the biggest distance from the hinges

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2
Q

What can turning effects also be called?

A

Moments

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3
Q

What does a lever do?

A

Changes the size of a force

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4
Q

What is the effort?

A

The force you exert on the lever

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5
Q

What is the load?

A

The force that the object being moved exerts on the lever

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6
Q

What is the pivot / fulcrum?

A

The point the lever turns about

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7
Q

What is the frequency and wavelength of X-rays?

A

~ High frequency

~ Very short wavelength (about the size of an atom)

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8
Q

What does the high frequency of X-rays mean?

A

They have a high energy and can cause ionisation

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9
Q

What is the high ionising power of X-rays used for?

A

Killing cancer cells in radiotherapy

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10
Q

X-rays are transmitted by healthy tissue, what is this property used for?

A

CT scans to detect soft tissue problems (eg disease, tumours, embolisms and haemorrhages)

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11
Q

X-rays are absorbed by bones and metals, what is this property used for?

A

Taking shadow pictures of bones to detect breaks and fractures

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12
Q

X-rays affect photographic film, what is this property used for?

A

Forming an image on an X-ray plate or with a CCD

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13
Q

What precautions are taken when using X-rays?

A

~ Use a focused beam so other parts of the body aren’t exposed
~ Technicians should take the X-ray from behind a screen or wear las clothing
~ Use as low a power as possible

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14
Q

What is the range of human hearing?

A

20Hz-20,000Hz

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15
Q

What happens as ultrasonic waves pass from one substance into another?

A

They’re partly reflected at the boundary (the time taken for these reflections is a measure of how far away the boundary is)

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16
Q

Reflected ultrasonic waves are usually processed to produce what?

A

A visual image on a screen

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17
Q

What is ultrasound used for?

A

~ Prenatal scans and other scans (eg detection of testicular cancer)
~ To break up kidney stones

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18
Q

How is ultrasound used in prenatal scans?

A

~ An ultrasound pulse is sent into the body and reflected back at different changes of density
~ These reflected waves are detected and used to form a picture of the foetus

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19
Q

What causes some of the ultrasound waves to be reflected?

A

Cracks within structures (the time taken for the reflected wave to return is used to calculate the location of the crack)

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20
Q

What can the vibrations caused by the ultrasonic waves be used for?

A

Cleaning delicate objects

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21
Q

What is the image quality and radiation exposure of CT scans?

A

~ Very good image quality

~ Longest exposure to ionising radiation

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22
Q

What is the image quality and radiation exposure of X-rays?

A

~ Good image quality

~ Short exposure to ionising radiation

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23
Q

What is the image quality and radiation exposure of ultrasound scans?

A

~ Good quality image depending on equipment

~ No exposure to ionising radiation

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24
Q

What is the process of bending light which is used in lenses?

A

Refraction

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25
Q

What are the 2 types of lens?

A

Diverging (concave) and converging (convex)

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26
Q

What is the difference between diverging and converging lenses?

A

They have a different curvature, so parallel rays of light pass through them differently

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27
Q

What is the focal length?

A

The distance from the lens to the principal focus

28
Q

What is a diverging (concave) lens like at its centre?

A

It’s thinnest

29
Q

What is a converging (convex) lens like at its centre?

A

It’s thickest

30
Q

What do the rays of light do in a double concave lens?

A

Refract outwards at the 2 curved boundaries so that they appear to come from one point, the focus

31
Q

What does only the middle ray in both diverging and converging lenses do?

A

Enters the lens at 90 degrees and passes straight through

32
Q

What do the rays of light do in a double convex lens?

A

They’re refracted inwards at the two curved boundaries to meet at one point called the focus

33
Q

What is the image produced by a converging (convex) lens like if the distance from the object to the lens is MORE than the distance from the lens to the focal point?

A

~ Real image
~ Inverted
~ Diminished
(the type of lens used in cameras)

34
Q

What is the image produced by a converging lens like if the distance from the object to the lens is LESS than the distance from the lens to the focal point?

A

~ Virtual image
~ Upright
~ Enlarged
~ Seems to be formed on the same side of the lens (the type of lens used in magnifying glasses)

35
Q

What is the frequency?

A

The number of waves passing a point per second

36
Q

What is ultrasound?

A

Sound waves of frequencies greater than 20,000Hz

37
Q

Why is ultrasound safer than using X-rays?

A

Ultrasound is non-ionising

38
Q

What is the image produced by a diverging (concave) lens like?

A

~ Virtual
~ Upright
~ Diminished

39
Q

What lens is used to correct short sightedness?

A

Diverging (concave) lens

40
Q

What do the ciliary muscles in the eye do?

A

Pull the lens for focusing

41
Q

What does the cornea in the eye do?

A

Lets light into the eye and begins focusing

42
Q

What does the iris in the eye do?

A

Controls the amount of light entering the eye

43
Q

What does the lens in the eye do?

A

Focuses light onto the retina

44
Q

What does the optic nerve in the eye do?

A

Sends signals to the brain

45
Q

What does the pupil in the eye do?

A

Let’s light through to the lens

46
Q

What does the retina in the eye do?

A

It’s a light sensitive layer that sends signals to the optic nerve

47
Q

What do the suspensory ligaments in the eye do?

A

Holds the lens in place

48
Q

How do you know whether the image produced through lenses is virtual or real?

A

Virtual images are formed from imaginary, dotted lines and are on the same side of the lens as the object

49
Q

How does ultrasound work through a transducer?

A

~ Ultrasound waves partially reflected when they meet different media
~ Time taken for reflections is measured
~ Each boundary distance is measured
~ Image formed on screen

50
Q

What does it mean if you’re short sighted?

A

~ The eyeball is too long or the lens is too fat

~ Close objects are in focus but distant objects are focused in front of the retina

51
Q

What does it mean if you’re long sighted?

A

~ The eyeball is too short or the lens is too thin

~ Distant objects are in focus but close objects are focused behind the retina

52
Q

What lens is used to correct long sightedness?

A

Converging (convex) lens

53
Q

How do eyes and cameras both allow light to enter?

A

~ Eyes use the pupil

~ Camera uses the aperture

54
Q

How do eyes and cameras both focus light?

A

~ Eye uses cornea and lens

~ Camera uses convex lens

55
Q

How do eyes and cameras both adjust focuses for different distances?

A

~ In the eye muscles and ligaments alter shape of lens

~ In cameras the lens moves closer to or further from the film/CCB chip

56
Q

How do eyes and cameras both control the amount of light entering?

A

~ In the eye the iris changes the pupil size

~ In cameras the diaphragm/aperture stop changes the aperture size

57
Q

How do eyes and cameras both form the images?

A

~ Eye uses the retina

~ Camera uses photographic film or CCD chip in digital cameras

58
Q

What is similar about the images produced by eyes and cameras?

A

They’re real, inverted and diminished

59
Q

What are lasers used for in medical physics?

A

~ Burning and cutting things
~ Cauterising (sealing off) things, such as damaged blood vessels
~ Reshaping cornea in laser eye surgery to enhance the bending of light that glasses would do

60
Q

What can total internal reflection be used for?

A

~ Sending light along optical fibres, which can be used for telephone calls and the Internet
~ With an endoscope for internal examinations which stops the need for surgery to look in the patients body. The optical fibre illuminates by shining a light through the fibre

61
Q

What is total internal reflection?

A

When all the rays are reflected and none are refracted

62
Q

When does total internal reflection happen?

A

When the angle of incidence is bigger than the critical angle

63
Q

How can the focal length be changed?

A

~ A more curved lens has a higher power and shorter focal length
~ A material with a high refractive index has a higher power and shorter focal length

64
Q

How can lenses be made flatter but with the same focal length?

A

By having a higher refractive index

65
Q

What is the unit for moments?

A

Nm

Physics (13 decks)

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