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Do X-rays have a long or short wavelength?
Short wavelength (and high frequency)
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What is the name of the process whereby x-rays can cause electrons to be removed from atoms?
Ionisation
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X-rays and ultrasound can be used to diagnose medical conditions. What does diagnose mean?
Find out what the problem is
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Is the wavelength of X-rays about the same size, much smaller or much larger than the diameter of an atom?
About the same size. This makes them useful for probing the structure of matter.
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Are X-rays transmitted or absorbed by healthy tissue?
Transmitted. (They are absorbed by bones)
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What is a Charge-Coupled Device (CCD) used for?
Detecting X-rays or visible light (digitally instead of using photographic film)
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What precautions should be taken when using X-rays?
- Minimise exposure,
- use lead shielding,
- use the minimum dose necessary,
- wear badges and detectors,
- label the area so people do not enter
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Why are X-rays more dangerous than ultrasound?
X-rays are ionising whereas ultrasound is not
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What is the name given to the process where light changes direction when it passes from one medium to another?
- Refraction
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Do lenses use refraction or reflection?
- Refraction
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What is the focal length of a converging lens?
- The distance from the lens to the point at which parallel rays are brought to a focus
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What is another name for a converging lens?
- Convex
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What is another name for a diverging lens?
- Concave
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Do converging lenses bring light rays together or move them apart?
Bring together
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What property of a material is defined by
Refractive index
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What 3 things define an image?
- Size (magnified or diminished),
- orientation (upright or inverted),
- type (real or virtual)
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What type of image does a converging lens produce?
Either a virtual or a real image depending upon how close the object is placed.. (Virtual if placed closer than the focal length - real otherwise)
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What type of image is produced by a converging lens when the object is placed at a distance f away from the lens?
No image is produced (as the rays will be leaving the lens parallel to each other)
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What is the difference between a real and a virtual image?
Real images can be projected onto a screen. (Light rays converge to a point for real images)
Virtual images cannot be projected onto a screen. (Light rays appear to come from a virtual image but they do not actually intersect each other)
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What is the nature of an image produced by an object placed less than f away from a converging lens?
Magnified, virtual, upright (this is using the lens as a magnifying glass)
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What is the nature of an image produced by an object placed at a distance between f and 2f away from a converging lens?
Magnified, real, inverted
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What is the nature of an image produced by an object placed at a distance of 2f away from a converging lens?
Same size, real, inverted
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What is the nature of an image produced by an object placed at a distance > 2f away from a converging lens?
Diminished, real, inverted
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How is the magnification of a lens calculated?
Image height / object height
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What is the purpose of the retina in the eye?
- It acts as a screen upon which an image can be projected.
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Which two parts of the eye are used to focus light?
- The lens and the cornea (which covers the iris and pupil)
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What is the coloured part of the eye called?
Iris
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What part of the eye is the pupil and what does it do?
It is the hole in the middle of the iris and it lets light into the eye
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What part of the eye controls the shape of the lens?
The ciliary muscles
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How do the ciliary muscles adjust the lens to make it more powerful?
The muscles contract which increases the curvature of the lens
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What connects the ciliary muscles to the lens?
Suspensory ligaments
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What name is given to the closest position at which a person can see an object clearly?
Near point
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What name is given to the furthest position at which a person can see an object clearly?
Far point
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What name is given to the distance between the near and far point?
Range of vision
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What is the near point for an average human with good eyesight?
About 25cm
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Cameras use film or CCDs to capture light. What is the equivalent part of the human eye?
Retina
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Why does the iris change the size of the pupil in the human eye?
To control the amount of light that enters. This enables people to see properly in a range of light conditions and prevents damage to the eye.
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Focussing in cameras is not done by altering the power of the lens like in the eye. How is it done?
By altering the distance between the lens and the film/CCD
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What is the name of the sight condition if someone can see distant objects clearly but not those close?
Long sight
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Can short-sighted people see objects clearly that are close or a long way away?
Close
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What is measured in dioptres (D)
The power of lenses
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What two things does the focal length (and hence its power) depend upon?
- How curved the two surfaces of the lens are,
- the refractive index of the material from which the lens is made.
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What is meant by the critical angle of a material?
The angle at which Total Internal Reflection (TIR) starts to happen
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Name some uses of optical fibres
- Endoscopes
- high-speed communication
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Lasers emit narrow beams of light. Name some uses for lasers
- Reading information on CD / DVD,
- in eye surgery to make very fine cuts or change the shape of the cornea,
- to cauterise blood vessels during surgery.
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