P3 Flashcards
What are X rays like
They are part of the electromagnetic spectrum
They have a high frequency and a very short wavelength
They have high energy and can cause ionisation
What are the uses of X rays
Can form an image on an X Ray plate or with a CCD (electronic image)
Can take shadow pictures of bones to detect breaks and fractures
Can scan to detect problems with soft tissue e.g. Disease
Used for killing cancer cells in radiotherapy
What are the precautions
Only use if necessary and use as low a power as possible
Use a focuses beam during treatments so as not to expose areas of the body not being treated or examined
Technicians should take the X rays from behind a screen or wear lead clothing
Technicians should wear detection badges, which measure their exposure over time
What is ultrasound
Sound waves of frequencies greater than 20 000Hz
What happens when and ultrasonic waves pass from one medium into another
They are partly reflected at the boundary. The reflected waves are usually processed to produce a visual image on a screen
How do you measure how far away the boundary is
The time taken for the ultrasonic waves to be reflected
What is the use of ultrasounds in medicine
The mains use is in prenatal scans but it can also be used for other scans e.f. Detection of gesticulating cancer
It can also be used to break up kidney stones which can then be passed out of the body in urine. This saves having to operate on their patients kidneys
How does an ultrasound on a baby work
An ultrasound pulse is sent into the body and gets reflected back at different changes of density. These reflected waves are detected and used to form a picture of the foetus. Because ultrasound is non ionising it is safer to use use than X rays
How do you locate a flaw or crack in a block of metal
Some ultrasound waves are reflected back by the flaw or crack within the structure. The time taken for the reflected wave to return is used to calculate the location of the crack
Best to worse image quality of scanning methods
CT scans
X rays
Ultrasound
Most to least radiation exposure
CT scans
X rays
Ultrasounds
What is refraction
What does it depend on
The change of direction of light as it passes from one medium to another
The refractive index of the material and the angle of incidence
What is a lens
What are the two types of lens
A piece of transparent material that refracts light rays
Diverging
Converging
What is the focal length
The distance from the lens to the principal focus
What is a diverging (concave) lens like
Thin at the centre
The rays of light are refracted outwards so that they appear to have came from one point, the focus
The image produced by a diverging lens is virtual and upright
What is a converging (convex) lens like
Thick at the centre
The light rays are refracted inwards to converge at one point called the focus
What does the image produced by a converging lens depend on
The distance of the object from the lens
What is the image like if the distance from the object to the lens is longer than the distance from the lens to the focal point in a converging lens
When is this type of lens used
Real image
Inverted
In cameras
What is the image like if the distance from the object to then lens is less than the distance from the lens to the focus point in a converging lens
When is this type of lens used
Virtual image
Upright
Enlarged
Seems to be formed on the same side of the lens
In magnifying glasses
What does the adjustable convex lens do
Focuses on the image
Why does someone need glasses
Their lenses are unable to focus the image correctly on the retina
What does the retina do
What do lenses do
What does the cornea do
What does the pupil do
Why does the iris do
Focuses images
Focuses the images
Protects the eye and begins to focus the light
Light enters the eye here
Adjusts to alter the amount of light entering the eye
What do suspensory ligaments do
What do ciliary muscles do
Connect the lens to the ciliary muscles
Contract and relax to alter the shape of the lens so the eye can focus on objects at different distances
In a camera:
What allows light to enter
What focuses the light
Adjusts focus for different distances
Controls amount of light entering
Forms the image
Aperture
Convex lens
Lens moves closer or further away from the film
Diaphragm/ aperture stop changes the aperture size
Photographic film or CCD chip
What so the range of vision in a normal eye
Between the near point ( around 25cm) and the far point (infinity)
What is the eye like if it’s short sighted
How do you correct short sightedness
The eyeball is too long or the lens is too fat. This means that near object are in focus, but distant objects are focused in front of the retina
Diverging lens
What is the eye like if it’s long sighted
How do you correct long sightedness
The eyeball is too short or the lens is too thin. This means that distant objects are in focus, but near objects are focuses behind the retina
What does the focal length and power depend on
The curvature- a more curved lens has a higher power and shorter focal length
The refractive index- a high refractive index has a higher power and shorter focal length
What is internal reflection
When a ray of light travels from glass into air, some light is reflected at the interface
When does total internal reflection occur
When the angle of incidence exceeds a certain value, called the critical angle
When is a total internal reflection used in medicine
With endoscopes for internal examinations, which removes the need for surgery to see inside the patients body. The optical fibre is used to provide illumination inside the body by shining a light through the fibre
What are the uses of lasers in medicine
Examples of surgical procedures using lasers
Cutting
Burning
Cauterising
Removing verrucas
Delicate laser eye surgery
What is the momentum
The turning effect of a force
How do you increase the moment
Increase the force applied
Increase the perpendicular distance between the line of action of the force and the pivot
What is the centre of mass of an object
The point through which the whole worthy of the object is considered to act
How do you find the centre of mass
Hang the sheet and a plumb line from one point so both are free to rotate. Mark the position of the plumb line as a vertical line
Hangs the sheet from a different position. Mark the position of the second plumb line
The centre of mass is the point where the two lines cross.
Why would a car topple over
If the line of action of the weight of the car lies outside its base, the car will topple over
How can the stability of car be increased
Lower centre of mass
A wider base
Why can’t liquids be compressed
The particles are close together
What happens when an object moves in a circle continuously
It accelerates towards the centre of the circle. This acceleration does not change the speed of the object, but the direction of its motion I.e. It’s velocity
The resultant force causing this acceleration is called the centripetal force
What 3 things can increase the centripetal force
The mass of the object increasing
The speed of the object increasing
The radius of the circle decreases
How is the size of the current increased (2)
Increases the size of the current
Increase the strength of the magnetic field
How is the direction of the force reversed (2)
Reverse the direction of flow of the current
Reverse the direction of the magnetic field
When is Flemings right hand rule used
To work out what direction the force induced will act
What does each finger and thumb show in Flemings left hand rule
The first finger points in the direction of the magnetic field
The second finger points in the direction of the current flow
The thumb will then be pointing in the direction of the force
What do transformers rely on to convert one voltage to another
Electromagnetic induction
How is a potential difference induced
How will a current be induced
If a wire or a coil of wire cuts through the lines of force of a magnetic field
If the wire is part of a complete circuit
How do you induce a current in one direction
Move the magnet into the coil
How can a current be induced in the opposite direction
By moving the magnet out of the coil
By moving the other pole of the magnet into the coil
Hal is the size of the induced potential difference increased
Increase the speed of movement of the magnet or the coil
Increase the strength of the magnetic field
Increase the number of turns on the coil
What does a transformer do
What do transformers consist of
Changes the electrical energy from one potential difference to another potential difference
Two coils called the primary and the secondary coils, wrapped around a soft iron core
How does the potential difference get from the primary coil to the secondary coil
An alternating potential difference across the primary coil will cause an alternating current to flow. This alternating current creates a continually changing magnetic field in the iron core, which induces an alternating potential difference across the secondary coil
What is a step up transformer like
There are more turns on the secondary coil than the primary coil so the potential difference is greater leaving the secondary coil than that of the primary coil
What is a step down transformer like
There are fewer turns on the secondary coil than the primary coil so the potential difference is lower leaving the secondary coil than that of the primary coil
What happens when the voltage increases
The current decreases
What are switch mode transformers
They are lighter and smaller than traditional transformers. They produce less heat and use very little power when no kid is applied. This makes them ideal for applications like mobile phone rechargers because their small size makes them more portable and once the phone is fully charged the transformer acts as a switch and so does not waste energy
