P3 1 - Medical applications of physics Flashcards
Properties of x-rays
Affect a photographic film similar to light
Can be absorbed by metal and bone
Are transmitted by healthy tissue
Why do CT scanners use x-rays?
CT scanners use x-rays to produce digital images of a cross-section through the body.
Why are x-rays dangerous?
X-rays cause ionisation and can damage living tissue when they pass through it.
Range of hearing for a human ear
20Hz-20kHz
How can a ultrasound wave give us an indication on how far away an object is?
When a wave meets a boundary between 2 different materials, part of the wave is reflected and travels back to a detector. The time it takes to reach the detector can be used to calculate how far away the boundary.
Equation for distance
Distance = speed x time
Advantages of using ultrasound instead of x-rays
Non-ionising - safer to use
Uses of ultrasound
Scanning unborn babies and soft tissue (e.g. The eye)
Shattering kidney stones
What is refraction?
The change of direction of light as it passes from one substance into another
Why does refraction occur?
Waves change speed when they cross a boundary. The change in speed of the waves causes a change in direction, unless the wave is travelling along a normal.
Equation for the refractive index
Sin (the angle of incidence) ÷ sin (the angle of refraction)
What is the critical angle?
The angle of incidence of a light Ray in a transparent substance which produces refraction along a boundary.
What happens when the angle of incidence increases beyond the critical angle?
Mum’s favourite thing about physics!
Angle of reflection = angle of incidence
Equation for the refractive index
1 ÷ sin (critical angle)
Range of hearing for a human ear
20Hz-20kHz
How can a ultrasound wave give us an indication on how far away an object is?
When a wave meets a boundary between 2 different materials, part of the wave is reflected and travels back to a detector. The time it takes to reach the detector can be used to calculate how far away the boundary.
Equation for distance
Distance = speed x time
Advantages of using ultrasound instead of x-rays
Non-ionising - safer to use
Uses of ultrasound
Scanning unborn babies and soft tissue (e.g. The eye)
Diagnosis and shattering of kidney stones
What is refraction?
The change of direction of light as it passes from one substance into another
Why does refraction occur?
Waves change speed when they cross a boundary. The change in speed of the waves causes a change in direction, unless the wave is travelling along a normal.
Equation for the refractive index
Sin (the angle of incidence) ÷ sin (the angle of refraction)
What is the critical angle?
The angle of incidence of a light ray in a transparent substance which produces refraction along a boundary.
What happens when the angle of incidence increases beyond the critical angle?
Mum’s favourite thing about physics!
Angle of reflection = angle of incidence
Equation for the refractive index
1 ÷ sin (critical angle)
What are the uses of x-rays?
They make images and CT scans
They destroy tumours at/near the body-surface
They are also used to challenge GCSE physics students
What is the refractive index of a substance?
It is a measure of how much the substance can reflect a light ray.
What is an endoscope?
It is a device to look inside a patient’s body without cutting it open or to perform keyhole surgery. It contains bundles of optic fibres. Visible light can be sent along the fibres by total internal reflection.
When will I, will I be famous?
I can’t answer, I can’t answer that
What is an optical fibre?
Very thin flexible glass tubes
What does a converging lens do?
It focuses parallel rays to a point called the principal focus. There is a principal focus on each side of the lens.
What is the focal length?
The focal length is the distance from the centre of the lens to the principal focus.
When is a real image formed by converging lens.
An inverted real image is formed if the object is further away than the principal focus. The nearer the object to the lens, the larger the image.
When is a virtual image formed by a converging lens?
If an object is nearer to the lens then the punk of thinkable focus and, and upright, virtual image is formed behind the object. Is the image is the magnified.
How do we calculate magnification?
Image height / object height
What happens to parallel rays of light that pass through a diverging lens?
They are refracted so that they diverge away from the principle focus
What type of image is produced by a diverging lens?
A virtual image
