P3.1 (Medical applications of physics) ( up to lenses) Flashcards
Relative to visible light, do X - rays have a short or long wavelength?
X- rays have a SHORT wavelength
only shorter waves = gamma rays
What type of waves are X-rays?
- TRANSVERSE WAVES
oscillations go up and down/ perpendicular to energy transfer
What is ionisation?
Adding or removing electrons from atoms
What are the useful properties of X-rays?
- 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
How can X-rays help identify broken bones and objects within the body?
- 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
How can X-rays be used to identify healthy and decaying teeth?
Decayed teeth do not absorb X-rays as well as healthy teeth so where the teeth are decayed, the paper will be darker
How do modern X-rays work without photographic paper?
Modern X-rays use CCDs (Charge Coupled Devices) in order to produce images electronically so they are more easily stored and shared
What are the benefits of CT scans over X-rays?
CT scans take multiple images to produce a 3D image that can be manipulated and viewed from more angles to identify further issues
What are negative side effects of X-rays?
- As they are IONISING, they can damage DNA in cells
- Although high doses of X-rays can kill cancer, low doses can cause it
How are X-rays used to treat cancerous cells in radiotherapy?
- High energy X-rays are directed at the cancerous cells
- This causes damage to the point of death of the cells
What substance can be used to protect radiographers from damage due to X-rays?
Lead
such as
Lead aprons
Lead barriers
What is the range of human hearing?
20 - 20,000 hz
Why can humans not hear ultrasound?
Ultrasound has a frequency of around 20,000 hz which is above the human range of hearing
How do ultrasounds produce images of inside the body?
- 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
What calculation measures the distance travelled by an ultrasound ray?
S = V x T
Distance (m) = Speed x Time
How can ultrasounds be used outside of medicine?
For quality control in products (eg metals) to check for cracks
How are ultrasounds used in medicine?
To monitor a baby’s growth
To treat kidney stones
What are kidney stones?
Solid crystals formed in urine that can pass into the ureter and block it causing immense pain
How can ultrasounds treat kidney stones?
A high frequency ultrasound is directed into the kidney stone causing it to vibrate and shatter into smaller pieces
How are X-rays and ultrasounds different?
- 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
What is refraction?
The change of direction of light as it passes through two substances of different densities
What happens to the speed of light when it enters a DENSER substance?
It SLOWS DOWN
Causing it to bend TOWARDS the normal
At what angle does refraction not happen?
If the light ray hits the object at 90degrees, it will not be refracted and will continue in a straight line
What is the refractive index?
The refractive index is the capability of an object to slow the speed of light
It is a RATIO rather than a measurement
How do you calculate the refractive index of a material?
Sin i (Angle of incidence) / Sin r (Angle of refraction)
Which direction does the glass bend in a CONVERGING lens?
The sides of the lens bend OUTWARD
It is represented by a line with arrows facing outwards
Which direction do converging lenses bend light?
Inwards to a focal point
How is the glass of a diverging lens arranged?
The glass bends INWARDS
It is represented with a vertical line with two arrows pointing inwards
What factors can be used to describe an image?
- Magnified / diminished
- Upright / inverted
- Real / Virtual
How do you calculate the ratio of magnification?
Magnification = Image height / Object height
