Medical Applications Of Physics Flashcards by Freya cracknell

What are the properties of X-rays

They affect a photographic film in the same way as light
They are absorbed by metal and bone
They are transmitted by healthy tissue

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What are X-rays used for

To form images of bones on photographic film to check for fractures and dental problems

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What do X-rays have

High frequency and a very short wavelength

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What are charged coupled devices used for

Forming electronic images of X-rays

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What do ct scanners do

Use X-rays to produce digital images of a cross section through the body

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How cansoft tissue be seen on a X-ray machine

Some body organs made of soft tissue such as the intestines can be filled with a contrast medium that absorbs X-rays so they can be seen on n X-ray image

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Why can X-rays damage living tissue

They are ionising

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How can workers protect themselves from X-rays

Wear film badges

Use lead screens to shield themselves

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What can X-rays be used to treat

They can be used to treat cancerous tumours or near the body’s surface

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What is the range that a human ear can hear

20-20000 hz

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What are ultrasound waves

Sound waves with a higher frequency than 20000 hz

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How can electronic systems produce ultrasound waves

When a wave meets a boundary between two different materials part of the wave is reflected. The wave travels back through the material to a detector. The time it takes to reach the detector can be used to calculate how far away the boundary is. The results may be processed by a computer to give an image

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In the time between sending out a pulse of ultrasound and it returning to a detector……….

It has travelled from the transmitter to a boundary and back, ie twice the distance to the boundary

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Why are ultrasound Ray’s safer than X-rays

They are non ionising

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How are ultrasounds used

Scanning unborn babies
Soft tissue such as the eye
Used in therapy eg to shatter kidney stones into small pieces

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What is refraction

The change in direction of light as it passes from one transparent substance into another

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Why does refraction take place

Waves change speed when they enter a boundary. The change in speed causes a change in direction

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When does refraction not take place when crossing a boundary

When the wave travels along the normal

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When a light Ray crosses from air into glasss……..

It is refracted towards the normal

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What is the refracted index

Is a measure of how much the substance can refract a light Ray

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Where are the angles I and r measured from

Between the Ray and the normal

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What way will a light Ray refract when it crosses from glass to air

Away from the normal

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WhAt is seen as a light Ray crosses from glass to air

A partially reflected Ray

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What happens if the angle of incidence is increased

The angle of refraction increases until the refracted Ray emerges along the boundary

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What is the angle of incidence also called when it is increased to the point where The angle of refraction increases until the refracted Ray emerges along the boundary

Critical angle

What happens if the angle of incidence goes beyond the critical angle

The light Ray undergoes total internal reflection

What happens when total internal reflection occurs

The angle of reflection is equal to the angle of incidence

What is an endoscope

A device used to look inside a patients body without cutting it open or when performing keyhole surgery

What does the endoscope contain and what are they

Optical fibres, very thin flexible glass fibres

How is visible light sent along optical fibres

By total internal reflection

What may be used as an energy source for endoscopy

Laser light

What can endoscopy procedures do

Cut, cauterise, burn

Why is the colour of light matched to the tissue in endoscopy

To produce maximum absorption

How does endoscopy eye surgery work

Using a laser light that passes straight through the cornea at the front of the eye but is absorbed by the retina at the back

What happens when parallel Ray's of light pass through a converging convex lens

They are refracted so that they converge to a point

What is the principal focus point

The point where light rays parallel to the principal axis of a lens are focuses or in the case of a diverging lens, appear to diverge from

What is the focal length

The distance from the centre of the lens to the principal focus

Why is there a principal focus on either side of the lens

Because light can pass through the lens in either direction

When is a real image formed

If the object is further away from the lens than the principal focus

What is a real image

An image formed where light rays meet

What does the size of the real image depend on

The position of the object, the nearer the object to the lens the larger the image

When is a virtual image formed

If the object is further away from the lens than the principal focus

What is a virtual image

An image seen in a lens of mirror from which light rays appear to come after being refracted by the lens or reflected by the mirror

If the object is further away from the lens than the principal focus and a virtual image is created what happens

The image is magnified, the lens acts as a magnifying glass

How Is magnification calculated

Image heigh divided by object height

What happens when parallel light rays pass through a diverging concave lens what happens

They are refracted so that they diverge away from a point. This point is called the principal focus

What is the focal length

The distance from the centre of the lens to the principal focus

What is the image produced by diverging concave lenses always

Virtual

What is a Ray diagram

A diagram can be drawn to find the position and nature of an image formed by a lens

What is the principal axis

A straight one that passes along the normal at the centre of each lens surface

What are the 3 construction rays from a single point on the object used to locate the corresponding point on the image

A Ray parallel to the principal axis is refracted through the principal focus A Ray through the centre of the lens travels straight on, without refraction A Ray through the principal focus is refracted parallel to the principal axis

Is the image formed in a camera real or virtual?

A camera uses a converging lens to form a real image of an object on a film or an array of CCDs

What does light enter the eye through

Cornea

What do the cornea and lens work to do

Focus the light on to the retina

What does the iris adjust

The size of the pupil

Why does the iris adjust the size of the pupil

To control the amount of light entering the eye

What do the ciliary muscles do

They alter the thickness of the lens to control the fine focus ing of the eye

What are the ciliary muscles attached to the lens with

Suspension ligaments

What is the retina

The light sensitive cells around the inside of the eye

What is the blind spot

Region where the retina is not sensitive to light (no light sensitive cells present)

What does the optic nerve do

Carries nerve impulses from the retina to the brain

What is the iris

Coloured ring of muscle that controls the amount. Of light entering the eye

What is the cornea

transparent layer that protects the eye and helps to focus light onto the retina

What is the pupil

The central hole formed by the iris. Light enters the eye through the pupil

What is a near point

the nearest point to an eye at which an object can be seen in focus by the eye.

What is the near point of a normal human eye

25cm

What is a far point

the furthest point from an eye at which an object can be seen in focus by the eye

What is the far post. Of a normal human eye

Infinity

What is the human range of vision

25cm to infinity

What does it mean to be short sighted

A person who can see close objects clearly, but distant objects are blurred because the I corrected image is formed in front of the retina

What is short sighted ness caused by

The eyeball being too long or the eye lens being too powerful

How is short sight corrected

Diverging lenses

What does it mean to be long sighted

They can see distant objects clearly, but close objects are blurred because the I corrected image is formed behind the retina

What is long sighted ness caused by

The eyeball being too short or the eye lens being too weak

How is long sightedness corrected

Converging lenses

What is the focal length determined by

The refractive index of the material from which the lens is made The curvature of the 2 surfaces of the lens

For a lens of a given focal length the greater the refractive index of the lens material,

The flatter and thinner the lens can be manufactured