P3 Physics AQA revision
This includes the basis of what we need to know for the P3 AQA GCSE exam... knowing these key points got me an A*
Ultrasound & X-rays: Cards 1-17
Lenses and eyes and using light: Cards 18-39
Centre of mass to moments and stabilty: Cards 40-49
Hydraulics: Cards 50-52 (oops not much to say)
Circular Motion: Cards 53-55
The motor effect: Cards 56-63
Includes almost everything except for the left hand rule and hydrolics
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- Created by: ZinaK - Team GR
- Created on: 21-05-13 10:32
What is sound?
Vibrations of a substance
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What is the range of human hearing?
20Hz to 20,000Hz
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What is ultrasound?
Vibrations of a frequency higher than 20,000Hz
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How does an ultrasound scanner work?
Ultrasound waves are released by a transducer, when the ultrasound waves meet different mediums, they are partially reflected. The time taken for the waves to come back is measured by the transducer.After calculating the distance an image is formed
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What is ultrasound used for?
Pre-natal scanning and treating kidney stones
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How do we treat kidney stones using ultrasound?
Instead of surgery, the method is to fire the ultrasound waves at the stones which break them down so they can pass out of the body as normal
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What are the advantages of using ultrasound rather than x-rays for pre-natal scanning?
It's non-ionising and produces accurate images of soft tissue
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What are x-rays?
Part of the electromagnetic spectrum
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What is the wavelength of an x-ray?
Around the width of an atom, therefore causes ionisation
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How do x-rays cause cancer?
As they are around the same size of an atom, it means that they can knock out electrons from atoms, causing ionisation which can cause damage in DNA and lead to mutations and can cause cancer
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How do X-rays affect photographic film?
In the same way as light
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What are X-rays absorbed by?
Metal and bone
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Explain how X-rays can be used to see broken bones:
The body part containing the potentially broken bone is placed above photographic film, the x-rays are then fired at the film, turning the bits that it hits black, because the bone absorbs the x-rays it cannot pass through, leaving the image of bone
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What does CT stand for?
Computerised tomography
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How does a CT scanner work
A person is placed in a tube, x-rays are emmited in all directions as the tube rotates, this is then connected to CCD so a digital image can be formed
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What are the safety precautions someone might take when using x-rays often?
Standing behind a lead door/shield or wearing a lead apron. Also special badges are worn that are checked on a regular basis to check if someone has had too high a dosage which can be seen on a film
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What are the comparative points between CT scanners and x-ray machines?
CT scanners produce a higher dose of x-ray, a 3D image is formed and it distinguishes between different soft tissues and bone, X-rays produce a lower dose, form a 2D image and are a lot cheaper
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What is refraction?
The changing of direction of light caused by travelling through a different media
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What is the refractive index?
A feature of specific materials related to how much light rays will refract
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What is the normal line?
A line which is at 90 degrees to a surface
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What happens when the ciliary muscle contracts?
The lens becomes short and wide
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If you are short sighted, does this affect short or long sight?
Long
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If you are short sighted, are you more likely to have a long or short eyeball
long
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How are cameras and the eye similar?
The image formed is real, diminished and inverted and also both use a converging lens
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How is the problem of short sightedness solved?
Using a diverging lense
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What are the differences between a camera and the eye?
In a camera the has a fixed focus, it changes by moving its position whilst in an eye it is achieved by the contraction of the ciliary muscles so has a variable focus. In a camera the image is focused on a film or CCD rather than the retina
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What is the focal length?
The distance between the principal focus and the lens
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What happens when parallel light rays pass through a convex lense?
They refract to pass through the principal focus
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When does a convex lens work like a magnifying glass?
When the object is between the lens and the principal focus
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How do we know an image is virtual?
The image is formed by imaginary light rays, it is often on the same side of the lens as the object
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What is the unit of power of a lens?
Dioptres
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How is the power different for a concave lens?
It is always negative
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What happens if the curvature of a lens is higher?
The focal length is smaller
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How else can the size of the focal length be reduced?
Using a material with a high refractive index
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How can a lens be made thinner whilst also keeping the focal length the same?
Using a material of a higher refractive index
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How can total internal reflection be used?
In optical fibres- an example of which is an endoscope
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What is an endoscope?
Can be used to see into the body, works as the light can be reflected
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What are lasers?
Intense and focused monochromatic light
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What are lasers used for?
Can be used with and endoscope to cauterise damaged blood vessels, they can cut, burn and can be used in laser eye surgery where a part of the cornea is burnt away
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What is the centre of mass?
The point at which the mass of an object may be thought to be concentrated
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How can the centre of mass be found?
Where the lines of symmetry meet- or if irregular it is directly below the point of suspension. A plumbline can be used, both the shape and plumbline must be freely suspended
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What is the name for a complete cycle of a pendulum?
A period
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What factor changes the period?
The length of the pendulum
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What is a moment?
The turning effect of a force
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What is a pivot?
The point around which the whole thing turns
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What is the unit of a moment?
Nm
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For any object to be balanced, what must be the same?
The anticlockwise and clockwise moments must be equal
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If the line of action of the weight lies outside the base...
There will be a resulting moment and the object will topple
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What can be done to increase an objects stability?
Wider base and lower centre of mass
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What happens to a liquid when pressure is applied?
It is transmitted equally in all directions as liquids are virtually incompressable
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What is the unit of pressure?
Pascals
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If something is moving in a constant speed in a circle, how can it be said to accelerating?
Acceleration=A change in velocity/Time The velocity is constantly changing as it moves in a circle therefore it is accelerating
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What is the direction of acceleration?
Towards the centre of the circle
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What is the centripetal force?
The resultant force that keeps an object moving in a circle- acts towards the centre and is caused by friction, tension in a string/spring, gravity
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What factors mean a bigger centripetal force is needed?
A higher speed, mass and a smaller radius
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What is produced around a wire when a current is put through it?
A magnetic field
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What can be done to increase the magnetic field in a wire?
Creating a coil - to increase it more you can add an iron core, add more current and have more coils
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Explain how a circuit works that uses an electromagnet:
The first circuit is switched, the electromagnet then carries a current so the magnet is switched on. The armature is then attracted which pivots around a point and attaches the contact which links the second circuit
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What is a relay circuit for?
A low current circuit switches on a high current circuit
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What is a circuit breaker?
If there is a surge in current, the electromagnet will become strong enough to attract a switch which therefore breaks the circuit
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How can we increase the force at which the wire moves in the field?
By increasing the current and the magnetic field
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How can the force be reversed?
By reversing the magnetic field or the current
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How does a loudspeaker work?
There is a permanent magnet behind and a wire around the cone that is inserted into the magnet, if the current changes direction and amount, the cone moves in and out
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What is induced from the secondary coil?
A potential difference- a step up's voltage will be larger than the primary's coil
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How does the power compare from one side of the transformer to the other?
Assuming it is 100% efficient its the same
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What is a switch mode transformer?
Works at a much higher frequency (1000 times more) - useful for devices like mobile phone chargers, it uses very little power when they are on
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Other cards in this set
Card 2
Front
What is the range of human hearing?
Back
20Hz to 20,000Hz
Card 3
Front
What is ultrasound?
Back
Card 4
Front
How does an ultrasound scanner work?
Back
Card 5
Front
What is ultrasound used for?
Back
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