P3.1 (Medical applications of physics) ( up to lenses)

Question 1

Relative to visible light, do X - rays have a short or long wavelength?

Answer 1

X- rays have a SHORT wavelength

only shorter waves = gamma rays

Question 2

What type of waves are X-rays?

Answer 2

• TRANSVERSE WAVES

oscillations go up and down/ perpendicular to energy transfer

Question 3

What is ionisation?

Answer 3

Adding or removing electrons from atoms

Question 4

What are the useful properties of X-rays?

Answer 4

• Absorbed by metal and bone (hard tissue)
• Pass through healthy / soft tissue
• Atom sized wave length (VERY SHORT)
• Affect photographic film (turns black) just like visible light

Question 5

How can X-rays help identify broken bones and objects within the body?

Answer 5

• White photographic film is placed behind patient
• When the x-rays are passed through area of concern, rays are absorbed by bones and hard tissue
• The remaining rays pass through and turn the paper black
• This leaves white area where broken bones can be identified

Question 6

How can X-rays be used to identify healthy and decaying teeth?

Answer 6

Decayed teeth do not absorb X-rays as well as healthy teeth so where the teeth are decayed, the paper will be darker

Question 7

How do modern X-rays work without photographic paper?

Answer 7

Modern X-rays use CCDs (Charge Coupled Devices) in order to produce images electronically so they are more easily stored and shared

Question 8

What are the benefits of CT scans over X-rays?

Answer 8

CT scans take multiple images to produce a 3D image that can be manipulated and viewed from more angles to identify further issues

Question 9

What are negative side effects of X-rays?

Answer 9

• As they are IONISING, they can damage DNA in cells

- Although high doses of X-rays can kill cancer, low doses can cause it

Question 10

How are X-rays used to treat cancerous cells in radiotherapy?

Answer 10

• High energy X-rays are directed at the cancerous cells

- This causes damage to the point of death of the cells

Question 11

What substance can be used to protect radiographers from damage due to X-rays?

Answer 11

Lead
such as
Lead aprons
Lead barriers

Question 12

What is the range of human hearing?

Answer 12

20 - 20,000 hz

Question 13

Why can humans not hear ultrasound?

Answer 13

Ultrasound has a frequency of around 20,000 hz which is above the human range of hearing

Question 14

How do ultrasounds produce images of inside the body?

Answer 14

• The ultrasound rays enter the body
• When the ray meets a boundary of two different densities, some of it is reflected back
• A device receives these reflected rays and produces an image from them

Question 15

What calculation measures the distance travelled by an ultrasound ray?

Answer 15

S = V x T

Distance (m) = Speed x Time

Question 16

How can ultrasounds be used outside of medicine?

Answer 16

For quality control in products (eg metals) to check for cracks

Question 17

How are ultrasounds used in medicine?

Answer 17

To monitor a baby’s growth

To treat kidney stones

Question 18

What are kidney stones?

Answer 18

Solid crystals formed in urine that can pass into the ureter and block it causing immense pain

Question 19

How can ultrasounds treat kidney stones?

Answer 19

A high frequency ultrasound is directed into the kidney stone causing it to vibrate and shatter into smaller pieces

Question 20

How are X-rays and ultrasounds different?

Answer 20

• X-rays have a shorter wavelength allowing them to provide more detailed imagery in order to identify small fractures
• CT scans also produce extremely detailed imagery
• Ultrasound waves are non ionising and safe to be exposed to a number of times

Question 21

What is refraction?

Answer 21

The change of direction of light as it passes through two substances of different densities

Question 22

What happens to the speed of light when it enters a DENSER substance?

Answer 22

It SLOWS DOWN

Causing it to bend TOWARDS the normal

Question 23

At what angle does refraction not happen?

Answer 23

If the light ray hits the object at 90degrees, it will not be refracted and will continue in a straight line

Question 24

What is the refractive index?

Answer 24

The refractive index is the capability of an object to slow the speed of light
It is a RATIO rather than a measurement

Question 25

How do you calculate the refractive index of a material?

Answer 25

Sin i (Angle of incidence) / Sin r (Angle of refraction)

Question 26

Which direction does the glass bend in a CONVERGING lens?

Answer 26

The sides of the lens bend OUTWARD

It is represented by a line with arrows facing outwards

Question 27

Which direction do converging lenses bend light?

Answer 27

Inwards to a focal point

Question 28

How is the glass of a diverging lens arranged?

Answer 28

The glass bends INWARDS

It is represented with a vertical line with two arrows pointing inwards

Question 29

What factors can be used to describe an image?

Answer 29

• Magnified / diminished
• Upright / inverted
• Real / Virtual

Question 30

How do you calculate the ratio of magnification?

Answer 30

Magnification = Image height / Object height