Medical Uses of Physics
Physics 1 X-Rays
●X-rays are part of the electromagnetic spectrum. They have a very short wavelength and cause ionisation.
●Properties of X-rays include:
■ they affect a photographic film in the same way as light
■ they are absorbed by metal and bone
■ they are transmitted by soft tissue
■ their wavelength is of the same order of magnitude as the diameter of an atom.
●X-rays can be used to diagnose and treat some medical conditions. Examples include CT scans, bone fractures, dental problems and killing cancer cells. The use of charge-coupled devices (CCDs) allows images to be formed electronically.
●Precautions to be taken when X-ray machines and CT scanners are in use.
Physics 2 Ultrasound
●Electronic systems can be used to produce ultrasound waves, which have a frequency higher than the upper limit of hearing for humans. Candidates should know that the range of human hearing is about 20 Hz to 20 000 Hz.
●Ultrasound waves are partially reflected when they meet a boundary between two different media.
The time taken for the reflections to reach a detector can be used to determine how far away such a boundary is.
●Calculation of the distance between interfaces in various media.
s=v×t
s is distance in metres, m
v is speed in metres per second, m/s
t is time in seconds, s
Candidates may be required to use data from diagrams of oscilloscope traces.
●Ultrasound waves can be used in medicine. Examples include pre-natal scanning and the removal of kidney stones.
●Compare the medical use of ultrasound and X rays. Candidates should understand that some of the differences in use are because ultrasound waves are non-ionising and X rays are ionising.
●Evaluate the advantages and disadvantages of using ultrasound, X-rays and Computerised Tomography (CT) scans. Limited to safety issues and the quality of image formed.
Physics 3 Refraction
●Refraction is the change of direction of light as it passes from one medium to another.
refractive index= sinisinr
i is the angle of incidence
r is the angle of refraction
Physics 4 Total Internal Reflection
●Total internal reflection and critical angle.
refractive index=1sinc
c is the critical angle
Candidates need to understand the concept of critical angle but knowledge of the values of critical angles is not required.
●Visible light can be sent along optical fibres. Examples of use should include the endoscope for internal imaging.
●The laser as an energy source for cutting, cauterising and burning. Knowledge of how lasers work is not required. Applications should include use in eye surgery.
Physics 1 X-Rays
Are X-rays longitudinal or transverse waves? ______
X-rays are part of the electromagnetic spectrum. Complete this list of the waves of the EM Spectrum by writing the initials of the waves in the correct boxes. X-rays has been added for you as has the colour green from the visible part of the spectrum.
X / Visible LightG
Which waves have:
The longest wavelength? ______The shortest wavelength? ______
The highest frequency? ______The lowest frequency? ______
The wavelength of X-rays is about the same size as ______
X-rays can cause ionisation. What does ionisation mean? ______
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What can low doses of ionising radiation cause? ______
What can high doses of ionising radiation cause? ______
X-rays are uses to create radiographs or X-ray photographs. X-rays are sent towards the patient and a lightproof cassette containing a photographic film is placed on the other side of the patient. The photographic film in the cassette is white before the radiograph it taken.
What are the common uses of radiographs?
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X-rays are absorbed by ______
X-rays are transmitted by ______
Explain how a radiograph like the one shown above is produced from a plain white piece of photographic film.
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Why does the radiographer go behind a screen before the X-ray machine is turned on?
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Explain why are lead lined shields are sometimes placed over some patients such as children and pregnant women.
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Describe what a CT scanner is, how it works and what it is used for. There is space to draw a diagram to support your description.
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What does a charge-coupled device (CCD) do?
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Explain the advantages of a CT scan compared to an X-ray.
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Explain the disadvantages of a CT scan compared to an X-ray.
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X-ray can also be used to destroy cancerous cells. These X-rays have a ______wavelength and a
______frequency than the X-rays used for diagnosis.
Physics 2 Ultrasound
Are ultrasound waves longitudinal or transverse waves? ______
What are ultrasound waves? ______
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What is the range of frequencies that humans can hear on average? ______to______
Some animals have the ability to produce ultrasound waves. How do humans produce ultrasound waves?
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What happens to an ultrasound wave when it reaches a boundary between two different materials?
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Students A and B walk at the same speed; I send student A to go to the restaurant and student B to go to the SID office. When the students reach their destination they then turn around and come back to the lesson.
What can you conclude if student A returns first? ______
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What can you conclude if student B returns first? ______
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What can you conclude if it takes A twice as long to return to the classroom?______
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Where in the Academy could the classroom be located? ______
s=v×t
Symbol / Quantity / Units / Unit Symbols
v
t
Rearrange the equation to make v and then t the subject.
An ultrasound scan can be used to make a picture of a baby in its mother’s womb. An ultrasound transmitter and detector are placed above the mother’s womb. Ultrasound goes into the body of the mother and into the body of the baby. Explain how the picture is formed by describing what happens to the ultrasound waves.
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How else are ultrasound waves commonly used in medicine? ______
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The diagram shows how a very high frequency sound wave can be used to check for internal cracks in a large steel bolt. The oscilloscope trace shows that the bolt does have an internal crack.
Explain what happens to produce pulse A and pulse B.
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The speed of sound through steel is 6000 m/s.
Calculate the distance from the head of the bolt to the internal crack if each horizontal box has a value of:
0.000 005 seconds 0.000 002 seconds
Compare the use of ultrasounds, X-rays and CT scans in terms of:
What they would be used for.
Ultrasound______
X-rays______
CT scans______
The quality of image formed.
Ultrasound______
X-rays______
CT scans______
The safety issues involved.
Ultrasound______
X-rays______
CT scans______
Physics 3 Refraction
Are light rays longitudinal or transverse waves? ______
What does reflection mean in terms of light rays? ______
What does refraction mean in terms of light rays? ______
When does refraction happen? ______
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When light travels from one material to another the ______will change.
If the material is more difficult to move through it will ______
If the material is easier to move through it will ______
The diagrams below show a ray of light leaving a ray box, travelling through material A and entering material B.In both diagrams continue the line from the ray box as a straight, dotted line through B and back into A to use as a reference line.
In this diagram material B is more difficult to move through compared to material A.
Draw the path of the ray through B and out into A again. / In this diagram material B is easier to move through compared to material A.
Draw the path of the ray through B and out into A again.
If light travels into a material that it is more difficult to move through is will bend ______the normal.
If light travels into a material that it is easier to move through is will bend ______the normal.
What would happen if the ray of light was shone down the normal? ______
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refractive index=sinisinr
Symbol / Quantity / Units / Unit Symboli
r
You can represent the refractive index with the symbol n to make it easier to rearrange.
Rearrange the equation to make sin i and then i the subject. Rearrange the equation to make sin r and then r the subject.
What are the units of sin i and sin r? ______
What are the units of the refractive index? ______
Complete this table by calculating the missing values.
i ( ) / r ( ) / sin i / sin r / Refractive Index55 / 32
85 / 45
15 / 1.45
75 / 1.45
20 / 1.33
35 / 1.33
If light travels from one material to another of higher refractive index the speed of the light will ______
and the ray will ______the normal.
If light travels from one material to another of lower refractive index the speed of the light will ______
and the ray will ______the normal.
Physics 4 Total Internal Reflection
What is the critical angle?
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Complete these diagrams to support your explanation. In the diagrams the critical angle is 42°.
When the angle of incidence is:
Less than the critical angle the ray of light will ______
Equal to the critical angle the ray of light will ______
Greater than the critical angle the ray of light will ______
refractive index=1sinc
Symbol / Quantity / Units / Unit Symbolc
You can represent the refractive index with the symbol n to make it easier to rearrange.
Rearrange the equation to make sin c and then c the subject.
Calculate the refractive index of the glass semi-circles in the previous diagrams / In the first semi-circle diagram the angle of incidence is 20°. Calculate what the angle of refraction should be.What are the common uses of optical fibres (also called fibre optics)?
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Complete the diagram to show the path taken by the light ray as it travels through the optical fibre.
Why does the ray of light stay inside the optical fibre? You can label parts of the diagram and use it to help with your explanation.
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The diagram shows an endoscope being used by a doctor to look inside a patient’s stomach. Light travels into the stomach through a bundle of optical fibres. The following sentences describe how the endoscope allows the doctor to see inside the patient’s stomach. Rearrange the sentences into the correct order.
The reflected light passes through a second bundle of optical fibres. / 3 /Light passes through a bundle of optical fibres into the patient’s stomach. / 1
The doctor looks through the eyepiece to see inside the patient’s stomach. / 5
The inside of the stomach reflects some of the light. / 2
The optical fibres take the light to an eyepiece. / 4
What would be the alternative to using an endoscope for this job?
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What are the advantages of using an endoscope for this job?
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What are the three uses of a laser other that as a source of light?
1______2______3______
Give situations where lasers are used in the ways listed above.
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What safety procedures should we follow when using a laser?
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Lenses and Vision
Physics 5 Lenses
●A lens forms an image by refracting light.
●In a convex or converging lens, parallel rays of light are brought to a focus at the principal focus. The distance from the lens to the principal focus is called the focal length.
●The nature of an image is defined by its size relative to the object, whether it is upright or inverted relative to the object and whether it is real or virtual.
●The focal length of a lens is determined by:
■ the refractive index of the material from which the lens is made, and
■ the curvature of the two surfaces of the lens.
Physics 6 Ray Diagrams
●The nature of the image produced by a converging lens for an object placed at different distances from the lens.
●In ray diagrams a convex lens will be represented by:A concave lens will be represented by:
●The use of a converging lens as a magnifying glass.
●The nature of the image produced by a concave or diverging lens.
●The construction of ray diagrams to show the formation of images by converging and diverging lenses. Candidates may be asked to complete ray diagrams drawn on graph paper.
●The magnification produced by a lens is calculated using the equation:
magnification=image heightobject height
●Draw and interpret ray diagrams in order to determine the nature of the image.
Physics 7 The Eye
●The structure of the eye. The structure of the eye is limited to:
■ retina
■ lens
■ cornea
■ pupil /iris
■ ciliary muscle
■ suspensory ligaments.
Candidates should know the function of these named parts. Candidates should understand how the action of the ciliary muscle causes changes in the shape of the lens, which allows the light to be focused at varying distances.