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Medical Uses of PhysicsPhysics 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, mv is speed in metres per second, m/st 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= sin isin r
i is the angle of incidencer is the angle of refraction
Physics 4 Total Internal Reflection●Total internal reflection and critical angle.
refractive index= 1sin c
c is the critical angleCandidates 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.
XVisible Light
GWhich 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 UltrasoundAre 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 ×tSymbol Quantity Units Unit Symbol
svt
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 RefractionAre 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= sin isin r
Symbol Quantity Units Unit Symbol
ir
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 Index
55 3285 4515 1.4575 1.45
20 1.3335 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 ReflectionWhat 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= 1sin c
Symbol Quantity Units Unit Symbol
cYou 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. 3Light passes through a bundle of optical fibres into the patient’s stomach. 1The doctor looks through the eyepiece to see inside the patient’s stomach. 5The 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 VisionPhysics 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.●Range of vision. The eye can focus on objects between the near point and the far point. Candidates should know that the near point is approximately 25 cm and the far point is infinity.●Comparison between the structure of the eye and the camera. Candidates should be aware that the film in a camera or the CCDs in a digital camera is the equivalent of the retina in the eye.
Physics 8 Correcting Vision●Correction of vision using convex and concave lenses to produce an image on the retina:
■ long sight, caused by the eyeball being too short, or the eye lens being unable to focus■ short sight, caused by the eyeball being too long, or the eye lens being unable to focus.
●The power of a lens is given by:
P=1f
P is power in dioptres, Dfis focal length in metres, m
Candidates should know that the power of a converging lens is positive and the power of a diverging lens is negative.●For a given focal length, the greater the refractive index, the flatter the lens. This means that the lens can be manufactured thinner.●Evaluate the use of different lenses for the correction of defects of vision.
Physics 5 LensesWhat does ‘refract’ mean? __________________________________________________________________________________
When does it happen? _____________________________________________________________________________________
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Lenses refract light and have many uses. List some of these uses.
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When dealing with light and lenses it is important to use the correct vocabulary. Explain what the following words mean when used to describe an image produced through a lens.
Inverted _________________________________________________________________________________________________
Upright __________________________________________________________________________________________________
Magnified ________________________________________________________________________________________________
Diminished ______________________________________________________________________________________________
Real ____________________________________________________________________________________________________
Virtual __________________________________________________________________________________________________
Complete the above diagrams by labelling each type of lens and drawing what happens to the parallel rays of light after they have reached the lens. You may wish to add annotations to the diagrams.
What is meant by the term ‘focal point’? ________________________________________________________________________
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What is meant by the term ‘focal length’? _______________________________________________________________________
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What two factors will affect the focal length of a lens?
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Physics 6 Ray Diagrams
Look at another different objects through a convex lens. Describe how they appear (compared to normal) when:A) You hold the lens near to your eye and look at an object that is a few centimetres away.
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B) You hold the lens near to your eye and look at an object that is a few metres away.
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Now using a concave lens, describe how they appear when:C) You hold the lens near to your eye and look at an object that is a few centimetres away.
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D) You hold the lens near to your eye and look at an object that is a few metres away.
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When drawing ray diagrams how are the two types of lenses represented?
Converging lens
Diverging lens
To complete the ray diagram showing the formation of images using a converging lens follow these steps:
1. Draw a line from the _____________________________________________________________________________________
2. Continue this line ________________________________________________________________________________________
3. Draw a line from the _____________________________________________________________________________________
4. The image is formed where ________________________________________________________________________________
To complete the ray diagram showing the formation of images using a diverging lens follow these steps:
1. Draw a line from the _____________________________________________________________________________________
2. Continue this line ________________________________________________________________________________________
3. Draw a line from the _____________________________________________________________________________________
4. The image is formed where ________________________________________________________________________________Complete this ray diagram to show how the lens produces an image of the object.
State three words to describe the nature of the image produced by the lens.
1______________________________ 2______________________________ 3______________________________
Complete this ray diagram to show how the lens produces an image of the object.
F O FL
E y e
State three words to describe the nature of the image produced by the lens.
1______________________________ 2______________________________ 3______________________________
Complete this ray diagram to show how the lens produces an image of the object.
FO b jec t
D iv e rg in g le n s
E y e
State three words to describe the nature of the image produced by the lens.
1______________________________ 2______________________________ 3______________________________
M= IO
Symbol Quantity Units Unit Symbol
MIO
Rearrange the equation to make I and then O the subject.
A magnification greater than 1 means ___________________________ and less than 1 means ___________________________
Calculate the magnification for the ray diagrams that you have completed.
Physics 7 The EyeHere is a diagram of the eye, label the different parts.
Explain the function of the different parts of the eye.
Retina __________________________________________________________________________________________________
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Lens ___________________________________________________________________________________________________
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Cornea _________________________________________________________________________________________________
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Pupil and Iris _____________________________________________________________________________________________
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Ciliary Muscle ____________________________________________________________________________________________
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Suspensory Ligaments _____________________________________________________________________________________
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How do we change our focus from near objects to those in the distance?
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What is the range of human vision? ___________________________________________________________________________
How is the structure of the eye similar to the structure of a camera?
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How is a camera changed to focus on objects at different distances (near and far)?
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What is used instead of photographic film in a digital camera? _______________________________________
Physics 8 Correcting VisionEach of our eyes has a lens that can change shape to focus on near and far objects. Complete the diagrams to show rays of light from near and far objects focused onto the retina (at the back of the eye). This would be described as normal vision.
Near objects Far objects
Some people are ‘short sighted’. Explain what this means and complete ray diagrams to demonstrate this.
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Near objects Far objects
Some people are ‘long sighted’. Explain what this means and complete ray diagrams to demonstrate this.
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Near objects Far objects
Explain how short sightedness is corrected. You should include which type of lens is used and a ray diagram like those before.
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Explain how long sightedness is corrected. You should include which type of lens is used and a ray diagram like those before.
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P=1f
Symbol Quantity Units Unit Symbol
Pf
Rearrange the equation to make f the subject.
Calculate the power of the lenses in Lesson 6.
Will the power of a converging (convex) lens be positive or negative? ________________________
Will the power of a diverging (concave) lens be positive or negative? ________________________
For a given focal length, the ____________________ the refractive index, the ____________________ the lens. This means that the lens can be manufactured thinner.
Moments and StabilityPhysics 9 Moments●The turning effect of a force is called the moment.●The size of the moment is given by the equation:M=F×d
M is the moment of the force in newton-metres, NmF is the force in newtons, Ndis the perpendicular distance from the line of action of the force to the pivot in metres, m
●If an object is not turning, the total clockwise moment must be exactly balanced by the total anticlockwise moment about any pivot.●The calculation of the size of a force, or its distance from pivot, acting on an object that is balanced.●Ideas of simple levers. Limited to levers as force multipliers.
Physics 10 Centre of Mass●The centre of mass of an object is that point at which the mass of the object may be thought to be concentrated. Candidates will be expected to be able to describe how to find the centre of mass of a thin, irregular sheet of a material.●If freely suspended, an object will come to rest with its centre of mass directly below the point of suspension.●The centre of mass of a symmetrical object is along the axis of symmetry.
Physics 11 Stability and Toppling●If the line of action of the weight of an object lies outside the base of the object there will be a resultant moment and the body will tend to topple. Applications should include vehicles and simple balancing toys.●Analyse the stability of objects by evaluating their tendency to topple. Candidates should use a range of laboratory equipment to model real-life situations, eg cranes.●Recognise the factors that affect the stability of an object. Candidates should recognise that objects with a wide base and low centre of mass are more stable than those with a narrow base and a high centre of mass.●Evaluate how the design of objects affects their stability.
Physics 9 MomentsWhat is a moment? ________________________________________________________________________________________
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How can you identify the pivot in any situation involving moments?
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M=F×dSymbol Quantity Units Unit Symbol
MFd
Rearrange the equation to make F and then d the subject.
Calculate the moment created in each of the three situations shown below.
If an object is not turning then the _____________________ clockwise moments are _________________________________ the
_______________________________________________________________ moments.
Complete this table by calculating the missing values for a balanced see-saw.Anticlockwise Clockwise
F d M M F d
250 0.3 1.2300 3.2 750
2.4 6000 6.4400 160 1.75
Levers are simple machines or devices that use the principles of moments.
In a lever system what is the effort? __________________________________________________________________________
In a lever system what it the load? __________________________________________________________________________
Using the appropriate key terms explain which lever should be used to move the rock.
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Here is a diagram of a device that is uses the principle of moments to measure the mass
Describe how the device would be used to measure the mass of an object and explain how it works.
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Physics 10 Centre of MassWhat is the centre of mass of an object?
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If a thin object is hung from the wall by a single pin where will the centre of mass be?
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If a student hangs from a beam with both hands where will their centre of mass be?
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If the student lets go of one hand where will their centre of mass be now?
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Find the centre of mass for each of these shapes.
Here is the method for finding the centre of mass of a thin, irregular shaped sheet of cardboard. Rearrange the sentences into the correct order.
A line is drawn on the card marking the position of the string.The nail is put through one of the holes in the card and held in the boss.
This is repeated using the other hole.
Two holes are made in the card with each hole near to the edge of the card.
The centre of mass is where the lines cross on the card.
The weight is tied to the string and then the string is hung from the nail
Why is the string and weight used to help draw the line?
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How could you ensure that your location of the centre of mass is accurate?
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Physics 11 Stability and TopplingWhat is meant by the line of action of a force?
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Where do we draw the line of action of the weight starting from? _____________________________________________________
In which direction does it act? ________________________________________________________________________________
Some objects can by tilted to a large angle before they topple over but others only need to be tilted by a small angle.When will a tilted object topple over?
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When will a tilted object stay upright?
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A wooden brick is tilted so that it leans to the right like in the diagram.What can we say about the resultant moments if the object stays upright?
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What can we say about the resultant moment if the object topples over?
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If I stand on one foot where must my centre of mass be? __________________________________________________________
How do you increase the stability of an object?
A ______________________________________________________________________________________________________
B ______________________________________________________________________________________________________
How do you decrease the stability of an object?
A ______________________________________________________________________________________________________
B ______________________________________________________________________________________________________
The drawing shows a toy that can stand on its feet. Draw an X where the centre of mass of the toy is likely to be.Suggest ways in which the design of the toy could be altered to make the toy more stable.
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Swings and RoundaboutsPhysics 12 Pendulums●For a simple pendulum:
T=1f
T is periodic time in seconds, sf is frequency in hertz, Hz
●The time period depends on the length of a pendulum. Applications of the pendulum should include simple fairground and playground rides.
Physics 13 Circular Motion●When an object moves in a circle it continuously accelerates towards the centre of the circle. This acceleration changes the direction of motion of the body, not its speed. Candidates should be able to identify which force(s)provide(s) the centripetal force in a given situation.●The resultant force causing this acceleration is called the centripetal force and is always directed towards the centre of the circle.●The centripetal force needed to make an object perform circular motion increases as:
■ the mass of the object increases■ the speed of the object increases■ the radius of the circle decreases.
●Interpret and evaluate data on objects moving in circular paths. Candidates should understand that a centripetal force does not exist in its own right but is always provided by something else such as gravitational force, friction or tension.
Physics 14 Hydraulics●Liquids are virtually incompressible, and the pressure in a liquid is transmitted equally in all directions. Candidates should understand that this means that a force exerted at one point on a liquid will be transmitted to other points in the liquid.●The use of different cross-sectional areas on the effort and load side of a hydraulic system enables the system to be used as a force multiplier.●The pressure in different parts of a hydraulic system is given by:
P= FA
P is the pressure in pascals, PaF is the force in newtons, NA is the cross-sectional area in metres squared, m2
Physics 12 PendulumsA simple pendulum can be made by ______________________________________________
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What is meant by ‘the time period’ of a pendulum? You can use the diagram to help you.
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The time period of a pendulum is depends on ________________________________________________________________
The _____________________________________________________________the _______________________ the time period.
Why would you measure the time taken for 10 swings to work out the time period of a pendulum instead of just 1 swing?
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T=1f
Symbol Quantity Units Unit Symbol
Tf
Rearrange the equation to make f the subject
A pendulum makes 10 complete swings every 160 seconds. Calculate the frequency of the pendulum.
What are the energy transformations occurring as the pendulum travels from:
A to B? _____________________________________________________________________________________________
B to C? _____________________________________________________________________________________________
A student found that after each swing the pendulum did not return to the same height as it set off from (point A became lower and lower after each swing). Explain why this happens.
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What are the common uses of pendulums?
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Physics 13 Circular MotionThe ____________________ force causing an object to __________________________________ is called the centripetal force.
This force always acts _______________________________________________________________
This makes an object accelerate ________________________________________________________________
Explain how an object moving in a circle at constant a speed can be accelerating.
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What provides the centripetal force in the following situations?1. A child sat on a spinning roundabout. _______________________________________
2. A satellite orbiting the Earth. _______________________________________
3. A car driving around a roundabout. _______________________________________
4. A toy aeroplane flying around a lamppost. _______________________________________
5. A ball on a string being spun in a vertical circle. _______________________________________
6. A ball on a string being spun in a horizontal circle. _______________________________________
What would happen to the ball if the string snapped in situation 6?
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What would happen to the Earth if the force of gravity from the Sun increased?
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What would happen to the Earth if the force of gravity from the Sun decreased?
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The diagram shows a ‘G-machine’. The G-machine is used in astronaut training.
If the following changes were made to the G-machine what would need to happen to the centripetal force required?
The speed of the machine was
increased
The speed of the machine was
decreased
The mass of the astronaut was
increased
The mass of the astronaut was
decreased
The radius of rotation was increased
The radius of rotation was decreased
Physics 14 HydraulicsDraw diagrams to show the how that atoms are arranged in the different states of matter.
Solid Liquid Gas
Use your diagrams to help you explain why gases are compressible but solids and liquids are virtually incompressible.
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P= FA
Symbol Quantity Units Unit Symbol
PFA
Rearrange the equation to make F and then A the subject.
The pressure in a liquid is transmitted _________________________________________________________________________
The diagram shows a simple hydraulic jack. The jack is designed to lift a large weight using a much smaller force.
This is an example of a force ______________________Calculate the pressure created on the small piston by the force of 50 N pushing downwards.
What would the pressure at Y be? __________________
Calculate the upwards force at the large piston if it has an area of: 65 cm2. 85 cm2.
In a hydraulic system what is the effort? _______________________________________________________________________
In a hydraulic system what it the load? _______________________________________________________________________
ElectromagnetismPhysics 15 Electromagnets●When a current flows through a wire a magnetic field is produced around the wire. Applications of electromagnets could include their use on cranes for lifting iron/steel.●Interpret diagrams of electromagnetic appliances in order to explain how they work.
Physics 16 The Motor Effect●The motor effect and its use. Candidates should be able to apply the principles of the motor effect in any given situation.●The size of the force can be increased by:
■ increasing the strength of the magnetic field■ increasing the size of the current.
●The conductor will not experience a force if it is parallel to the magnetic field.
●The direction of the force is reversed if either the direction of the current or the direction of the magnetic field is reversed. Candidates will be expected to identify the direction of the force using Fleming’s left-hand rule.
Physics 17 Induction●If an electrical conductor ‘cuts’ through a magnetic field a potential difference is induced across the ends of the conductor.●If a magnet is moved into a coil of wire a potential difference is induced across the ends of the coil.
Physics 18 Transformers●The basic structure of the transformer.●An alternating current in the primary coil produces a changing magnetic field in the iron core and hence in the secondary coil. This induces an alternating potential difference across the ends of the secondary coil. Knowledge of laminations and eddy currents in the core are not required.●In a step-up transformer the potential difference across the secondary coil is greater than the potential difference across the primary coil.●In a step-down transformer the potential difference across the secondary coil is less than the potential difference across the primary coil.
Physics 19 Using Transformers●The potential difference across the primary and secondary coils of a transformer are related by the equation:V p
V s=n pns
Vp is the potential difference across the primary coil in volts, VVs is the potential difference across the secondary coil in volts, Vnp is the number of turns on the primary coilns is the number of turns on the secondary coil
●If transformers are assumed to be 100% efficient, the electrical power output would equal the electrical power input.V p×I p=V s×I s
Vp is the potential difference across the primary coil in volts, VIp is the current in the primary coil in amperes (amps), AVs is the potential difference across the secondary coil in volts, VIs is the current in the secondary coil in amperes (amps), A
Candidates should be aware that the input to a transformer is determined by the required output.●Switch mode transformers operate at a high frequency, often between 50 kHz and 200 kHz.●Switch mode transformers are much lighter and smaller than traditional transformers working from a 50 Hz mains supply. Candidates should be aware that this makes them useful for applications such as mobile phone chargers.●Switch mode transformers use very little power when they are switched on but no load is applied.●Compare the use of different types of transformer for a particular application. Examples might include some mobile phone chargers and power supplies for lap top computers.
Physics 15 ElectromagnetsHow do you create an electromagnet?
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How could you increase the strength of an electromagnet?
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Here is a diagram of the equipment used by a student to investigate the strength of five different electromagnets.
The stronger the electromagnet, ________________________________
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Why is it important that the paper clips used in the investigation are all the same size?
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The five electromagnets, J, K, L, M and N, used by the student are shown below. Each electromagnet was made by wrapping lengths of insulated wire around identical iron nails.
The student wants to find out how the strength of an electromagnet depends on the number of turns of wire in the coil.
Which electromagnets should the student compare in order to do this? _______________________________________________Explain your answer
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What conclusions can be made from the data in the diagram?
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The student makes one more electromagnet by winding 100 turns onto a nail. If a current of 1 amp flows through the wire how many paper clips would you predict that the electromagnet could lift?
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What are the common uses of electromagnets?
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The diagrams show a relay switch and how it is used in a car ignition circuit.
Turning the ignition key closes the ignition switch. Explain how this causes the starter motor to operate.
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Physics 16 The Motor EffectWhen a conductor carrying an electric current is placed in a magnetic field a force may act on it.How could you reverse the direction of the force experienced by the wire?
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B _______________________________________________________
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How could you increase the size of the force experienced by the wire?
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B _______________________________________________________
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In what circumstance will no force act on a conductor carrying an electric current and in a magnetic field?
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Fleming’s left-hand rule can be used to find the direction of the force.
What does the thumb represent? ________________________________________________
What does the first finger represent? ________________________________________________
What does the second finger represent? ________________________________________________
Use Fleming’s left-hand rule to find the direction of the force that the current carrying wire would experience in the following situations.
The arrow represents the direction of the current with meaning the current is out of the page and meaning into the page.
A _____________________________________________ D _____________________________________________
B _____________________________________________ E _____________________________________________
C _____________________________________________ F _____________________________________________
Explain your answer to situation F.
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The diagram shows a coil placed between the poles of a magnet. The arrows on the sides of the coil itself show the direction of the current. The arrows labelled F show the direction of the forces acting on the sides of the coil.
Why do the different sides of the coil experience forces in opposite directions?
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Why won’t the coil spin?
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Physics 17 InductionA potential difference can be ______________________________ by moving a magnet in a coil of wire or moving a wire through a
magnetic field. In both situations an electrical conductor ______________ through the magnetic field ____________________
If the conductor is part of a complete circuit the potential difference will cause a _________________________________________
How could you reverse the direction of the induced potential difference?
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B ______________________________________________________________________________________________________How could you increase the size of the induced potential difference?
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B ______________________________________________________________________________________________________
C ______________________________________________________________________________________________________
The diagram shows a student’s design for a renewable way of generating electricity.Explain why the wind causes the voltmeter to give a reading.
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Why will the potential difference be alternating?
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Why is iron used in the coil of wire?
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Physics 18 TransformersWhat is the job (or role) of a transformer?
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Here is a diagram of the basic structure of a transformer.
What is the part labelled as A called? __________________________________
What is the part labelled as B called? __________________________________
What material is it made from? __________________________________
What is the part labelled as C called? __________________________________
There are step-up and step-down transformers.How can you tell if a transformer is a step up transformer just by looking at it?
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Complete this table for a step-up transformer.
Primary Coil Secondary Coil
Number of coils
Potential difference
How can you tell if a transformer is a step-down transformer just by looking at it?
________________________________________________________________________________________________________Complete this table for a step-down transformer.
Primary Coil Secondary Coil
Number of coils
Potential difference
When a current flows in the primary coil it creates a _______________________________________________________________
This means that the magnetic field lines ________________________________________________________ the secondary coil.
This means that_________________________________________________________________________ in the secondary coil.
The current in the primary coil then ____________________________________________________________________________
This means that the magnetic field ____________________________________________________________________________
and it cuts the secondary coil ________________________________________________________________________________
This means that it induces __________________________________________________________________________________
Explain why insulated wires are used to make the coils.
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Explain why iron is used for the core of a transformer.
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Explain why a transformer would not work if a direct current was used.
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Physics 19 Using TransformersThe potential difference across the primary and secondary coils of a transformer are related by the equation:
V p
V s=n pns
Symbol Quantity Units Unit Symbol
Vp
Vs
np
ns
Rearrange the equation to make Vp and then Vs the subject.
Rearrange the equation to make np and then ns the subject.
Complete this table by calculating the missing values and filling in the last column. Give your answers to 1 decimal place.
Vp Vs np ns Step-up or step-down?
100 300 20240 9 30120 1000 250
28 180 50
If we assume that a transformer is 100 _____________________________________________, the electrical power out of the
transformer would _____________________________________________________ the electrical power into the transformer.
V p×I p=V s×I sSymbol Quantity Units Unit Symbol
Vp
Vs
Ip
Is
Rearrange the equation to make Vp and then Vs the subject.
Rearrange the equation to make Ip and then Is the subject.
Complete this table by calculating the missing values and filling in the last column. Give your answers to 1 decimal place.
Vp Vs Ip Is Step-up or step-down?
6 24 3128000 230 5
922 0.15 2.11003 3.1 1.3
Transformers are used in the National Grid. Add labels to this diagram of the National Grid.
Why is the potential difference increased after it leaves the power station?
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What is the frequency of transformers used in the National Grid? _______________________ Hz
Switch mode transformers operate at frequencies higher than those used in the National Grid.
Between which frequencies do they operate? _______________________ and _______________________ Hz.
How are switch mode transformers physically different from those used in the National Grid?
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What are switch mode transformers typically used for?
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Explain why they are suitable/appropriate for these uses. You should do this in terms of energy and their physical structure.
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