P3.1

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Describe the basic properties of X-rays.
They’re part of electromagnetic spectrum, have a high frequency + a short wavelength (wavelength = same size as diameter of an atom).
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Describe the properties of X-rays that make them useful for medicine.
X-rays affect a photographic film in the same way as light, are absorbed by metal + bone & are transmitted by healthy tissue.
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What are CT scanners?
As they are charge-coupled scanners –use X-rays to produce digital images of a cross-section through the body. Some soft tissue body organs can be filled with a contrast medium that absorbs X-rays so they can be seen on an X-ray image (intestines).
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How can X-rays be used?
For therapy to treat cancerous tumours at or near the body surface + to form images of bones on photographic film to check for fractures + dental problems.
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Why should precautions be taken when using X-rays?
As they cause ionisation + can damage living tissue when they pass through living tissue. Workers should wear film badges + use lead screen to shield them from X-rays.
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What are ultrasound waves?
Sound waves with a higher frequency than human hearing which is between 20Hz and 20,000Hz. In the time between a transmitter sending out a pulse of ultrasound and it returning to a detector, it has travelled from the transmitter to a boundary + back.
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How can electric systems be used to produce ultrasound waves?
When wave meets boundary between 2 different materials, wave partially reflected. Wave travels back through the material to a detector - time it takes to reach the detector used to calculate how far away boundary is-results processed by computer to g
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What can ultrasound be used for?
For scanning unborn babies (as its non-ionising) + soft tissue such as the eye. Ultrasound can also be used in therapy i.e. to shatter kidney stones into small pieces.
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What is refraction?
Change of direction of light as it passes from one transparent substance into another. The waves change in speed as they cross a boundary and so change direction unless the waves are travelling along a normal.
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What is the refractive index of a substance?
A measure of how much the substance can refract a light ray (n = sini/sinr).
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What happens when a light ray crosses from glass to air?
It is refracted away from the normal and a partially reflected ray is also seen.
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What is the critical angle?
(when the light ray passes from glass to air) -If the angle of incidence in the glass is gradually increased, the angle of refraction increases until the refracted ray emerges along the boundary.
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What is total internal reflection?
When the angle of reflection is equal to the angle of incidence. When the angle of incidence is increased beyond the critical angle, the light ray undergoes total internal reflection.
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What is an endoscope?
A device used to look inside a patient’s body without cutting it open/performing keyhole surgery –contains optical fibres (very thin, flexible glass fibres). Visible light can be sent along the fibres by total internal reflection.
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How can laser light be used?
As an energy source in an endoscope to carry out surgical procedures i.e. cutting, cauterising + burning. Colour of laser light is matched to the type of tissue to produce maximum absorption.
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How is eye surgery on the retina carried out?
By using laser light that passes through the cornea at the front of eye but is absorbed by the retina at the back.
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What is the principal focus (focal point)?
Parallel rays of light that pass through a converging (convex) lens are refracted so that meet at this point. As light can pass through the lens in either direction there’s a principal focus on both sides.
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What is the focal length?
The distance from the centre of the lens to the principal focus.
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How can an inverted, real image be formed by a converging (convex) lens?
If the object is further away from the lens than the principal focus, an inverted real image is formed. The size of the image depends on the position of the object. The nearer the object to the lens, the larger the image.
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How can an upright, virtual image be formed by the converging (convex) lens?
If the object is nearer to the lens, an upright, virtual image is formed behind the object. The image is magnified –the lens acts as a magnifying glass.
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How can magnification be calculated?
Image height / object height
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Describe what happens when parallel rays of light pass through a diverging (concave) lens.
They are refracted so that they diverge away from a point. This point is called the principal focus. As light can pass through both ends, there’s a principal focus on either side of the lens. The image produced by this lens is always virtual.
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What are three things you need to know for the ray diagram?
A ray parallel to the principal axis (line at centre of lens) is refracted through principal focus. Ray through centre of lens travels straight on (no refraction). Ray through principal focus is refracted parallel to principle axis.
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What are the functions of the front five features of the eye?
Cornea-transparent layer that protects eye + helps focus light onto retina. Iris: coloured ring of muscle that controls amount of light entering eye. Pupil: central hole light enters through. Eye lens: focuses light onto retina. Ciliary muscles
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What are the ciliary muscles, retina, blind spot and optic nerve?
Ciliary muscles: attached to lens by suspensory ligaments + the muscles change the thickness of the eye lens. Retina: light-sensitive cells around inside of eye. Blind-spot: region where retina is not sensitive to light. Optic nerve-carries nerve imp
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How is the power of a lens calculated?
1/focal length. The normal human eye has a near point of 25 cm + a far point of infinity so its range of vision is from 25 cm to infinity.
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How can a person with short sight see close objects clearly but find distant objects blurred?
As the uncorrected image is formed in front of the retina. Short sight is caused by the eyeball being too long or the lens being too powerful. Short sight may be corrected using a diverging lens.
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How can a person with long sight see distant objects clearly but find close objects blurred?
Close objects are blurred as the uncorrected image is formed behind the retina. Long sight is caused by the eyeball being too short or the eye lens being too weak –may be corrected using converging lens.
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What determines the focal length of a lens?
The refractive index of the material from which the lens is made + the curvature of the two surfaces of the lens. The greater the refractive index of the lens material, the flatter + thinner the lens can be manufactured.
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Other cards in this set

Card 2

Front

Describe the properties of X-rays that make them useful for medicine.

Back

X-rays affect a photographic film in the same way as light, are absorbed by metal + bone & are transmitted by healthy tissue.

Card 3

Front

What are CT scanners?

Back

Preview of the front of card 3

Card 4

Front

How can X-rays be used?

Back

Preview of the front of card 4

Card 5

Front

Why should precautions be taken when using X-rays?

Back

Preview of the front of card 5
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