Term
| Describe the purpose of the Cornea. |
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Definition
| A transparent 'window' with a convex shape, and a high refractive index. Does most of the eye's focusing. |
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Term
Describe the purpose of the Iris. |
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Definition
| The coloured part of the eye made up of muscles that controls the size of the pupil. |
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Term
Describe the purpose of the Pupil. |
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Definition
| The hole in the middle of the iris. This controls the intensity of light entering the eye. |
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Term
Describe the purpose of the Lens. |
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Definition
| This changes shape to focus light from objects at varying distances and is connected to the Ciliary Muscles and the Suspensory Ligaments. |
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Term
Describe the purpose of the Ciliary Muscles. |
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Definition
When they contract - tension is released and the Lens forms a fat spherical shape.
When they relax - the Lens is pulled into a thinner, flatter shape. |
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Term
Describe the purpose of the Retina. |
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Definition
| Here the images are formed because it is covered in light-sensitive cells which detect light and send signals to the brain. |
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Term
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Definition
A = Vitreous Humour (Not relevant for GCSE)
B = Lens
C = Cornea
D = Pupil
E = Iris
F = Sclera (Not relevant for GCSE)
G = Optic Nerve
H = Retina |
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Term
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Definition
| The furthest distance that the eye can focus comfortably. |
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Term
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Definition
| The closest distance that the eye can focus comfortably. |
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Term
| What happens as the Eye focuses on closer objects? |
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Definition
| The power increases - the Lens changes shape and the focal length decreases. |
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Term
| Describe the image formed by a camera. |
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Definition
| The image on the film is: A Real Image (because the light rays actually meet there), Smaller (because the object is a lot further away than the focal length of the lens) and Inverted. |
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Term
| How come we don't see things upside down? |
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Definition
| Because our clever brain flips the image the right way up. |
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Term
| What is the equivelent of the Retina in a camera? |
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Definition
| Charge Coupled devices (CCD's) which are silicon chips about the size of a postage stamp, divided up into a grid of millions of identical pixels. |
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Term
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Definition
| High frequency, short wavelength electromagnetic waves. |
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Term
| Name five advantages of X-Rays. |
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Definition
1. They are used to diagnose many medical conditions such as bone fractures or dental problems.
2. They can be used to treat cancer by being focused onto the tumour using a wide beam to kill the cells.
3. Painless and non-invasive.
4. Quick process.
5. Requires no recovery time. |
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Term
Name five disadvantages of X-Rays. |
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Definition
1. They are ionising (will damage or kill cells in your body) and so may increase your risk of developing cancer in the future.
2. Not possible during pregnancy due to the growing baby developing abnormalities.
3. X-rays only form a 2D image.
4. The image formed is not in real time.
5. Cannot see soft tissue because the X-rays are not absorbed by the tissue, only bone (dense materials). |
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Term
| What are Computerised Axil Tomography (CT) scans? |
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Definition
| These scans use X-rays to produce high resolution images of soft and hard tissue (because soft tissue can absorb small amounts of X-rays so lots more are used in CT scans than in normal X-rays). |
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Term
| Name three precautions that Radiographers should take to minimise radiation dose from X-rays. |
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Definition
1. Wear lead aprons (because X-rays are absorbed be lead).
2. Stand behind a lead screen or.....
3. Leave the room. |
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Term
| How is Short-Sightedness corrected? |
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Definition
| A diverging lens (with a negative power) is put in front of the eye. This diverges light before it enters your eye meaning the lens can focus it on the retina. |
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Term
How is Long-Sightedness corrected? |
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Definition
A converging lens (with a positive power) is put in front of the eye. This refracts and converges light before it enters your eye meaning the lens can focus it on the retina.
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Term
| Describe Laser Eye surgery. |
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Definition
| A laser is used to vapourise some of the cornea to change its shape and therefore its focusing ability so images can focus properly on the retina. |
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Term
| How do Optical Fibres work? |
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Definition
| They work by bouncing waves off the sides of a thin inner core of glass or plastic. The wave enters one end and is reflected repeatedly until it emerges at the other end. They work due to Total Internal Reflection. |
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Term
| When does Total Internal Reflection happen? |
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Definition
| It can only happen when a wave travels through a dense medium like glass or water towards a less dense medium like air. |
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Term
| What happens if the Angle of Incidence is... less than the Critical angle? |
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Definition
| Most of the light passes out but a little bit is internally reflected. |
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Term
What happens if the Angle of Incidence is... equal to the Critical angle? |
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Definition
| The emerging ray comes out along the surface - there's a lot of internal reflection. |
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Term
What happens if the Angle of Incidence is... greater than the Critical angle? |
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Definition
| No light comes out - it is all internally reflected (total internal reflection). |
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Term
| Complete the sentence - If a material has a high refractive index, it will... |
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Definition
| ...totally internally reflect more light. |
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Term
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Definition
| A thin tube containing optical fibres that lets surgeons carry out operations inside the body. There are two bundles of optical fibres: One to carry light to the area of interest and one to carry the image back so it can be viewed. The image can be seen through an eyepiece or as a full-colour moving image on a TV screen. |
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Term
| Name the main advantage of using an Endoscope. |
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Definition
| Surgeons can now perform many operations by only cutting very small holes in people meaning there is less recovery time needed (keyhole surgery). |
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Term
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Definition
| A very high frequency sound wave above 20,000 Hz (above the range of human hearing). |
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Term
| What happens when Ultrasound Waves enter a different medium? |
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Definition
| When a wave passes from one medium into another, some of the waves are reflected off the boundary between the two media and some is transmitted (refracted). This is Partial Reflection. |
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Term
| How does Ultrasound Imaging work? |
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Definition
| A pulse of Ultrasound is pointed at an object and wherever there are boundaries between mediums, some of the Ultrasound gets reflected back. The time it takes for the reflections to reach a detector can be used to measure how far away the boundary is. |
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