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42 Cards in this Set
- Front
- Back
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What properties do X-rays have? |
X-rays are high frequency, short wavelength electromagnetic waves. Their wavelength is roughly the same size as the diameter of an atom |
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How do X-rays work? |
They are transmitted through healthy tissue but are absorbed by denser materials such as metal and bones. |
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How are X-rays formed electronically? |
Charged- coupled devices (CCDs) are silicon chips about the same size as a postage stamp. They detect X-rays and produce electronic signals which are used to form hogh resolution images. |
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What are C.T scans? |
Computerised axial tomography (CT) scans use X-rays to produce high resolution images of soft and hard tissue. |
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How do C.T scans form a 3D image? |
X-rays are passed through the patient and many 2D images are put together forming a 3D image of inside the body. |
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How do X-rays treat cancer? |
X-rays are carefully focused to ionise cancer cells without damaging too many healthy cells. X-rays are focused on the tumour using a wide beam. The beam is rotated round the patient with the tumour to minimise healthy cell exposure. |
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What precautions must be taken around X-rays and C.T scanners? |
X-ray dosage needs to be minimised by workers- they wear lead aprons; stand behind the screen or leave the room. Patients have lead shields across the areas of the body that are not being scanned and exposure time is always kept to a minimum. |
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What is the human hearing range and what is ultrasound? |
20-20,000Hz A higher frequency of the upper limit (20,000Hz) is ultrasound. |
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What happens to ultrasound at the boundary between two mediums? |
The ultrasounds are partially reflected (some are reflected/transmitted&refracted) The time it takes for reflections to reach the detector calculates the distance. |
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How can an oscilloscope trace be used to find boundaries? |
If the speed of sound in the medium is known--> the distance can be worked out by: s=v*t s=distance (m) v=speed (m/s) t= time (s) |
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What is ultrasound used for? |
Breaking down kidney stones- ultrasound beams concentrated high energy waves at the kidney stone which turns them into sand like particles. These are removed by coming out of the body in the urine. Pre-natal scanning- Ultrasound waves pass through the body but as they reach a boundary between two media, some of the wave is reflected back and detected. These echos are processed by a computer to produce a video image of the fetus |
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What are the pros&cons of X-rays,C.T scans and ultrasound? |
X-rays & C.T scans are ionising whilst ultrasound is not ionising and much safer Ultrasound images are fuzzy whilst X-rays are clear. C.T scans are very detailed with high resolution. |
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What is an endoscope? |
A tube containing optical fibres used for surgery. They contain two bundles of optical fibres-one to carry light to the area of interest and one has a camera so an image can be seen. |
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How do optical fibres work? |
Visible light is bounced off the sides of a thin inner core of glass using total internal reflection. The critical angle is very important (42 degrees in glass) |
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How do lasers help in eye surgery? |
A laser vaporises some of the cornea changing its shape which changes the focusing ability so it focuses on the retina correctly. |
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How is long sight corrected? |
Using a converging lens--> light refracts and so the image can be focused on the retina. |
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How is short sight corrected? |
Using a diverging lense--> the lens can focus on the retina which helps to focus on distant objects. |
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How does a camera focus an image? |
Light is refracted by a lens forming an image on the film (real image) but it is smaller than the actual image. |
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What do the components of the eye do? |
CORNEA--> transparent window with a high refractive index for focusing light. IRIS--> coloured part of the eye controlling light intensity entering the eye. LENS--> changes shape to focus light CILIARY MUSCLE& SUSPENSORY LIGAMENTS--> changes the shape of the eye. RETINA--> images form and sent via the optical nerve to the brain. |
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What is the focal point of the eye? |
Minimum=25cm |
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How is the focal length of a lens determined? |
Refractive index of the material and the curvature of the two surfaces of the lens. |
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What are the powers for converging and diverging lenses? |
Converging lens=positive Diverging lens=negative |
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How are the focal length and power of a lens related? |
Power= 1/focal length Power=D Focal length=m |
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How can magnification be calculated? |
Magnification= image height/object height |
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Where must an object be magnified? |
The object being magnified must be closer to the lens than the focal length. |
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What lens is used in magnifying glasses and cameras? |
Converging lens |
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What does a diverging lens always produce? |
A virtual image--> the right way up, smaller than the object and on the same side as the object on the lens. |
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What does a distance of less than F from the object to a lens do to the image? |
A object closer than F will produce a virtual image the correct way up. It will be bigger than the object on the same side as the lens |
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What does a diatance of between 2F and F from the object to a lens do to the image? |
An object between F and 2F will make a real,inverted image bigger than the object and beyond 2F. |
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What does a distance of 2F from the object to a lens do to the image? |
An object at 2F will produce a real,inverted image the same size as the object. |
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What is a virtual image? |
A virtual image is when the rays are diverging so the light from an object appears to be coming from a different place. |
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What is a real image? |
A real image is where the light from an object comes together to form an image on a 'screen' e.g a image formed on an eye's retina |
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What are the 3 rules for refraction in a converging lens? |
1) An incident ray parrallel to the axis refracts through the lens and passes through the principal focus on the other side. 2) An incident ray passing through the principal focus refracts through the lens and travels parallel to the axis. 3) An incident ray passing through the centre of the lens carries on in the same direction |
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What are the 3 rules for refraction in a diverging lens? |
1)An incident ray parallel to the axis refracts through the lens,and travels in a line with the principal focus(so it appears to have come from the principal focus) 2) An incident ray passing through the lens towards the principal focus refracts through the lens and travels parallel to the axis. 3) An incident ray passing through the centre of the lens carries on in the same direction. |
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What is the focal length? |
The distance from the centre of the lens to the principal focus (occurs on each side of the lens). |
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What is the principal focus of a diverging lens? |
Where the rays hitting the lens are parallel to the axis they appear to all come from. |
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What is the principal focus of a converging lens? |
Where the rays hitting the lens parallel to the axis all meet. |
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What is the axis of a lens? |
A line passing through the middle of the lens. |
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What are the two main types of lens? |
Converging lens- CONVEX SHAPE Diverging lens- CONCAVE SHAPE |
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What is refraction? |
Refraction is the change in direction of a wave when entering a different medium (due to wave speed change). |
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What is the refractive index? |
Refractive index of a medium is the ratio of the speed of light in a vaccum to the speed of light in the medium. |
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What is the equation for refractive index? |
Refractive index= sin i/sin r i= incident ray r= refracted ray |
