P3- Medical applications of physics Flashcards
How are X-rays used?
- Broken/fractured bones.
- Security.
- Telescopes.
- Destroy tumours at or near the body surface.
What are X-rays?
- Part of electromagnetic spectrum.
- High frequency and very short wavelength.
How are X-rays produced?
By fast moving electrons, which smash into a metal plate causing x-rays to be emitted.
How are low intensity X-rays dangerous?
They can damage cells and cause cancer (ionsiation).
How are high-intensity X-rays dangerous?
They kill cells straight away.
Name 3 properties of X-rays.
- They affect a photographic film in the same way as light.
- They are absorbed by metal and bone.
- They are transmitted by healthy tissue.
Why do bones look like this in X-rays?
Denser objects such as bones absorb more x-rays than soft tissue so show up more on x-ray images.
What precautions do workers using X-rays take?
- Wearing film badges which monitor exposure.
- Use lead screens or stand in lead rooms to shield themselves from X-rays.
- Wearing lead aprons.
What is a CT scan?
A ‘computed tomography’ scan is an advanced technique that uses X-rays and CCDs.
X-rays are fired through the patient and a series of images, like slices, are produced which are processed by a computer to give a 3D image.
What are CCDs?
Charge-coupled devices can be used to form electronic images of X-rays.
How can body organs made of soft tissues be seen on an X-ray image?
Some body organs such as the intestines can be filled with a contrast medium that absorbs X-rays so they can be seen on an X-ray image.
What are ultrasound waves?
Ultrasound waves are sound waves above the frequency of 20,000 Hz (higher than the human ear can detect).
How can ultrasound waves be used to produce an image?
The waves travel back through the material to a detector. The time it takes to reach the detector can be used to calculate how far away the boundary is. The results can be processed by a computer to give an image.
When ultrasound passes through the body, some of it is reflected back. Why?
Because of the change in density as it passes from one medium to another.
What is sound?
Sound is vibrations, compressions and decompressions of air that the human ear can detect.
What is the speed of sound in air?
340m/s.
Name 5 uses of ultrasound.
- Scanning unborn babies.
- Navigation underwater (SONAR).
- Finding and breaking kidney stones.
- Used by animals for navigation & communication.
- Purification of water.
How can the distance travelled by an ultrasound pulse be calculated?
s = v x t
s= Distance travelled (m).
v= Speed of ultrasound (m/s).
t= Time (s).
*Remember: In the time between the transmitter sending out a pulse of ultrasound and it returning to the detector it has travelled twice the distance to the boundary.*
How can the depth of boundary below the surface be calculated?
1/2 x distance travelled.
Identify the disadvantages and advantages of using X-rays.
✅Fast- images available the same day or within the hour.
✅Painless & non-invasive.
✅Doesn’t require any special preparation.
✅Requires no recovery time.
❌Slower than ultrasound.
❌Not recommended for pregnant women.
❌Exposure to radiation= increased risk of developing cancer.
Identify the disadvantages and advantages of using ultrasound.
✅Non-invasive.
✅Accurate.
✅Considered risk-free as it doesn’t damage cells.
✅’Real-time’ video therefore image available immediately.
❌Images from deeper into body have progressively poorer resolution.
❌Relies on expertise of sonographer.
❌After 18 weeks pregnancy, scans are unlikely to show anything but major problems.
How does light refract from a less denser to a denser material?
Light slows down and bend towards the normal.
How does light refract from a denser material to a less dense material?
Lights speeds up and bends away from the normal.
What is refractive index?
Refractive index (n) is a measure of how much a substance can refract a light ray.
A measure of the speed of light through a material compared to the speed of light in a vacuum.
How can refractive index be calculated?
n= sini/sinr
n= refractive index.
sini= sine of the angle of incidence.
sinr= sine of the angle of refraction.
Why doesn’t refractive index have a unit?
Because it is a ratio.
Total internal reflection only occurs when…
- The angle of the light is above the critical angle.
- The light is travelling from a more dense to a less dense material.
What is the critical angle?
The critical angle is when the angle of incidence emerges along the boundary between the two materials.
How is light refracted when the angle of incidence is below the critical angle?
Light refracts, a little is reflected.
How is light refracted when the angle is above the critical angle?
Total internal reflection.
What shape is a converging lens and how does this refract rays?
A converging lens is always convex. Converging lenses make the rays that are coming in parallel converge to a point.
What shape is a diverging lens and how does this refract rays?
A diverging lens is always concave. Diverging lenses make parallel rays coming in diverge away from a point.
What symbol may be used in a ray diagram to represent a converging lens?
What symbol may be used in a ray diagram to represent a diverging lens?
What type of image is formed by a converging lens when the object is beyond 2F?
- Real.
- Inverted.
- Diminished.
- Between F and 2F.
What type of image is formed by a converging lens when the object is on 2F?
- Real.
- Inverted.
- Same size as object.
- On 2F.
What type of image is formed by a converging lens when the object is between 2F and F?
- Real.
- Inverted.
- Magnified.
- Further than 2F.
What type of image is formed by a converging lens when the object is on F?
No image formed.
What type of image is formed by a converging lens when the object is infront of F?
- Upright.
- Virtual.
- Magnified.
- Same side as object.
What type of image is always formed by a diverging lens?
- Virtual.
- Upright.
- Diminished.
- Closer to lens than object.
What is the principal axis in a ray diagram?
The line through the centre of the lens and at right angles to it.
How do you draw a ray diagram for a converging lens?
A) A ray parallel to principal axis is refracted through the principal focus.
B) A ray through the centre of the lens travels straight on without refraction.
C) A ray through the principal focus is refracted parallel to the principal axis.
What is label 1-6?
1- Cornea.
2- Pupil.
3- Iris.
4- Lens.
5- Retina.
6- Ciliary muscle.
How is long sight caused?
1) The eyeball (distance between lens and retina) is too short.
2) Loss of elasticity in the lens so it cannot become fat enough to focus.
How do you draw a ray diagram for a diverging lens?
1) Draw a ray passing parallel to the principal axis and being refracted away from the principal axis.
2) Draw a ray directed at the principal focus behind the lens, but being refracted by the lens so that it runs parallel to the principal focus after leaving the lens.
3) Draw a ray passing in a straight line through the centre of lens without being refracted.
