3a) Medical Applications of Physics

Question 0

How can X-Rays be used in medicine?

Answer 0

X-Ray Photographs to diagnose bone fractures or dental problems

Question 1

Describe X-Rays

Answer 1

High frequency
Short wavelength (same as diameter of an atom)
EM waves
Transmitted though healthy tissue
Absorbed by denser materials like bones and metal

Question 2

What are CCDs

Answer 2

Charge-coupled devices
Silicon chips divided into a grid of millions of identical pixels
Detect X-Rays and produce electronic signals used to form high resolution images

Question 3

CT scans

Answer 3

Computerised axial tomography
Use X-Rays to produce high-resolution images if soft and hard tissue
Use more X-Rays that’s normal X-Ray photographs to distinguish small variations in tissue density

Question 4

X-Rays to treat cancer

Answer 4

X-Rays focused in tumour using a wide beam
Beam is rotated
X-Rays cause ionisation which kills the cancer cells
Doesn’t damage normal cells

Question 5

How do radiographers take precautions to minimise radiation dose?

Answer 5

Wear lead aprons
Stand behind lead screen
Leave the room during scans
Exposure time kept minimum

Question 6

What is ultrasound

Answer 6

Sound with a higher frequency than we can hear (higher than the upper limit of human hearing)

Question 7

What is partial reflection

Answer 7

Some of the wave reflected off the boundary between two media
Some is transmitted (and refracted) through the medium

Question 8

How can ultrasound be used in medicine?

Answer 8

Breaking down kidney stones into sand like particles that pass out of the urine
Pre-natal scanning of a fetus - ultrasound is reflected back from the fetus and detected to form an image

Question 9

Are ultrasound waves safe?

Answer 9

Yes

Non-ionising

Question 10

What is the law of reflection?

Answer 10

Angle if incidence = angle of reflection

Question 11

What causes refraction?

Answer 11

Change in direction of waves

Change in density of one medium to another medium

Question 12

What happens if a wave hits a boundary at 90 degrees (along the normal)

Answer 12

Will not change direction (won't be refracted)
Change speed (slow down)

Question 13

What is the refractive index of a medium?

Answer 13

Ratio of speed oh light in a vacuum to speed of light in the medium

Refractive index = sin i / sin r

Question 14

What happens when waves slow down?

Answer 14

They bend towards the normal

Question 15

Describe the two main types of lenses

Answer 15

Converging lens - convex shape, causes parallel rays of light to converge at principal focus
Diverging lens - concave shape, causes parallel rays of light to diverge (spread out)

Question 16

What is the axis of a lens?

Answer 16

Line passing through the middle of the lens

Question 17

What is the focal length?

Answer 17

Distance from the principal focus to the centre if the lens

Question 18

What is the principle focus for each type of lens?

Answer 18

Converging - where rays meet

Diverging - where the rays appear to come from

Question 19

Describe real and virtual images

Answer 19

Real image - light from an object comes together to form an image of a ‘screen’
Virtual image - rays diverge so the light appears to come from a different place (e.g mirror, magnifying glass)

Question 20

What is the word to describe an image that is upside down

Answer 20

Inverted

Laterally inverted - flipped from left to right

Question 21

How can the nature of an image be described?

Answer 21

How big image is compared to object (magnified/diminished)
Upright or inverted (upside down)
Real or Virtual

Question 22

What kind of image does a diverging lens produce?

Answer 22

Always virtual image

Question 23

Describe how distance from the converging lens affects the image

Answer 23

Object at 2F - real, inverted image, same size as object, at 2F
Between F and 2F - real, inverted image, Bigger than object, Further away than 2F
Nearer than F - virtual image, upright, bigger than object, on same side as lens

Question 24

How is short-sighted vision corrected?

Answer 24

Diverging lens

Causes image to move further back and form on the retina

Question 25

How is long-sighted vision corrected?

Answer 25

Converging lens

Causes image to move forward and form on the retina