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AQA GCSE Physics Unit 3 Mindmap
Description
A mind map on all of AQA GCSE Physics Unit 3 (not finished yet just need more pictures)
No tags specified
aqa
unit 3
medical
physics
gcse
magnets
motion
physics
gcse
Mind Map by
lauren_binney
, updated more than 1 year ago
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Gabi Germain
over 9 years ago
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lauren_binney
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Resource summary
AQA GCSE Physics Unit 3 Mindmap
Medical applications
X-rays
High frequency and short wavelength
Properties
Affect photographic film in the same way as light
Absorbed by metal and bone
Why lead aprons are worn
Absorb the rays and reduce exposure to radiation
Can cause cancer
Aswell as kill cancerous cells
At the surface
Near the surface of the body
Film badges
Show amount of exposure
Transmitted by healthy tissue
CCD
form electronic images
CT scanners
Digital cross-section
Soft tissue organs filled with contrast medium
Absorb X-rays to be seen
Ultrasound waves
Sound waves
With a frequency above 20,000Hz
Human ear
Detect sound waves between 20Hz and 20,000Hz
Produced by electronic systems
wave meets a boundary between 2 different materials
Part of the wave is reflected
Travels back through material to detector
Time taken to reach the detector can calculate how far away the boundary is
Results may be processed by a computer to produce an image
May need to half the time as it has travelled there and back
Non ionising
So its safer than X-rays
For scanning
Unborn babies (not unicorn)
And soft tissue
E.g. the eye
Not kleenex
Therapy
Shatter kidney stones
Refractive index
Refraction
The change of direction of light from one substance to another
Takes place because waves change speed when they cross a boundary
Because of the change in speed
How much a substance can refract a light ray
Sin i divided by Sin r
Incidence
Refraction
TAGAGA
Air to glass refracted towards the normal
Glass to air away from the normal
The endoscope
Critical angle
angle of incidence of a light ray in a transparent substance
Produces refraction along the boundary
If angle of incidence is higher than the critical angle the light ray under goes total internal reflection
When it occurs the angle of reflection is equal to the angle of incidence
Refractive index = 1 divided by sin c (critical angle)
Used to look inside a patients body
without cutting it open (bleh)
contain bundles of optical fibres
Thin, flexible glass fibres
Visible light sent along
By total internal reflection
Laser light may be used for cutting
Colour is matched to tissue type
To produce maximum absorption
Lenses
Converging (convex)
Used in magnifying glasses
If the object is NEARER to the lens than the principal focus, an upright virtual image is formed behind the object
If the object is FURTHER away from the lens than the principal focus an inverted real image is formed
Parallel light rays pass through and are refracted so they converge at a point called the principal focus
Diverging (concave)
If you go in a cave and there is a mean bear you will die (so a concave lens is diverging)
Light can pass through the lens in either direction there is a principal focus soon either side of the lens
Image is always virtual
Distance from the centre of the lens to the principal focus is the focal length
parallel light rays pass through and are refracted so they diverge away from a point, the principal focus
Magnification = image height divided by object height
Cameras use converging lenses to form a real image of an object on a film
Ray diagrams
Parallel to axis and through f
Through centre
Through F then parallel to axis
The eye
Iris - coloured ring of muscle that controls the amount of light entering the eye
Cornea - Transparent layer that protects the eye and helps focus light onto the retina (like corn which is yellow like light so it focuses light)
Retina the light sensitive cells around the inside of the eye
Pupil - The central hole formed by the iris and where light enters the eye through the pupil
Blind spot - region where the retina isn't sensitive to light
No light sensitive cells are present
Ciliary muscles - Attatched to the lens by suspensory ligaments to change the thickness of the eye lens
Optic nerve - carries nerve impulses to the brain
Eye lens - focuses light onto the retina
Conjuctiva membrane (its just there!)
Aqueous humour - transparent watery liquid that supports the front of the eye
Vitreous humour - transparent jelly like substance that supports the back of the eye
Eye muscles - move the eye in the socket
Power of a lens
= 1 divided by f (focal length)
Power of a lens is measured in deportees (D)
Focal length is measured in metres (m)
Human eye
Near point 25cm and a far point of infinity! (and beyond)
Range of vision
Eyeball defects may cause long or short sightedness (if thats a word)
Short sighted
See close objects clearly
distant objects are blurred
uncorrected image is formed in front of the retina
Eyeball being too long
eye lens too powerful
Corrected with a diverging lens
Long sighted
see distant objects clearly
the uncorrected image is formed behind the retina
Eye lens is too weak
Eyeball being to short
Corrected using a converging lens
Making things work
Hydraulics
Pressure
P = F divided by A
Measured in pascals, (not the chameleon from tangled) Pa
liquids are virtually incompressible
pressure in a liquid is transmitted in all directions
Made use of in hydraulic systems
Hydraulic pressure system
Force exerted depends on...
Force exerted on the system
Area of the cylinder on which the force acts
Area of the cylinder that the force is exerted on
Use of different cross sectional areas on the effort and load mean the system can be used as a force multiplier
Stability
The line of action of the weight of an object acts through its centre of mass
Line of action
lies outside the base of an object
topple over
resultant moment
Inside the base
Won't topple
The wider the base of an object
lower centre of mass
Has to tilt further to topple
Increased stability
Bowling pins narrow base so high centre of mass
Easily knocked over
Centre of mass
Where the mass of an object is though to be concentrated
When a suspended object is in equilibrium, its centre of mass is directly beneath its point of suspension
Finding the centre of mass
Symmetrical sheets where the axis of symmetry cross
Irregular sheets
suspend the sheet from a pin held in a clamp stand
Because it is freely suspended it is able to turn
Hang a plumb line from the same pin
Mark the position of the plumb line
Hang the sheet with the pin at another point and repeat the procedure
The centre of mass is where the lines cross
When it comes to rest
The position depends on the shape of the object which sometimes may lie outside the object
Pendulums
Moves to and fro along the same line
Oscillating motion
A simple pendulum consists of..
A mass (bob) suspended on the end of a string
when bob is displaced to one side and let go the pendulum oscillates
Through the equilibrium position
When it stops moving
Amplitude is the distance from the equilibrium position to the highest position on each side
Time period of an oscillation is the time taken for one complete cycle
To measure the time period of a pendulum
measure the average time fro 20 oscillations and divide the time by 20
Park swing is an example
depends on length, it increases as length increases
Time period = 1 divided by f (frequency (number of complete oscillations in one second))
Circular motion
Centripetal force increases when..
Mass increases
Radius decreases
Speed of the object increases
If centripetal force stops the object will continue to move in a straight line at a tangent to the circle
An object only accelerates when a resultant force acts on it
This force is called centripetal force and always acts towards the centre of a circle
Continuously changing direction
Continuously changing velocity
This acceleration is called centripetal force
Moments
Balance
If an object is in equilibrium the anticlockwise moment will be equal to its clockwise moment
This is the principal of moments
We use the principal of moments to calculate the force needed to stop an object turning
The turning effect of a force
M = F x d
d = perpendicular distance from the line of action of the force to the pivot in metres
To increase the moment of a force...
Increase the force
Increase the distance from the pivot
for example using a spanner
Using a lever
Force we are trying to move is called the load
The force applied to the lever is called the effort
Opening a door
Using a crowbar
Keeping things moving
Transformers
Two coils
Around wrapped around a laminated iron core
When an alternating current passes through the primary coil, it produces an alternating magnetic field in the core
This field continually expands and collapses
Easily magnetised
The alternating magnetic field passes through the secondary coil and induces an alternating potential difference along its ends
If the secondary coil is part of a complete circuit an alternating current is produced
coils of wire are insulated
doesn't short circuit on any adjacent turns of wire or the iron core
Switch mode transformer
Has a ferrite core (not ferret thats a cute fluffy animal)
Lighter and smaller
Operates at a higher frequency than a normal transformer
uses very little power when there is mo device connected across its output terminals
Step up or down
If pd across the secondary coil is higher than across the primary coil it is step up and the opposite for step down
Number of turns
Like a snowy mountain
The motor effect
when we place a wire carrying an electric current in a magnetic field it may experience a force
Maximum force if the wire is at 90 degrees to the magnetic field
Zero if parallel to the magnetic field
Flemings left hand rule
First finger is the direction of the magnetic field (north to south)
Second finger is the direction of the current
The thumb shows the motion the wire
Increase the force
Increase the current
Increase the strength of the magnetic field
To change the motion of the wire
reverse the direction of the magnetic field
reverse the direction of the current
electric motor
speed of the motor is increased by increasing the size of the current
direction reversed by changing current direction
coil spins when current goes through
force acts on each side due to the motor effect
Split ring commutator
Reverses coil current every half turn
Sides swap over each half turn the coil is always pushed in the same direction
Transformers in action
the national grid uses transformers to step-up the pd from power stations
The higher the pd at which electrical energy is transmitted across the grid the smaller the energy wasted in the cables
Step down transformers are used to reduce the pd so that it is safe to be used by consumers
Transformers are almost 100% efficient
1
2
There are two equations for transformers
Electromagnetic induction
If an electrical conductor cuts through magnetic field lines a potential difference is induced across the ends of the conductor
Increase the size of the induced pd...
Increase the speed of movement
Increase the strength of the magnetic field
Increasing the number of turns on the coil
so many turns!!
Reversing the direction of the movement or the magnetic field the direction of the pd is also reversed
pd is potential difference by the way
If a magnet is moved into a coil of wire a pd is induced across the ends of the coil, this process is called electromagnetic induction
Electromagnets
Magnets
Ends called magnetic poles
Region around the magnet in which pieces of iron will be attracted is called its magnetic field
Iron filings placed near a magnet will produce a pattern of lines that loop from one pole to the other, these are lines of force or magnetic lines
A plotting compass placed in the magnetic field will always point along the field line
Like poles will repel
Unlike poles will attract
When a current flows through a wire a magnetic field is produced around the wire
Made by wrapping an insulated wire around a piece of iron, iron core
When a current flows through the wire it becomes strongly magnetised
This temporary magnetism makes electromagnets very useful
If current is off it loses its magnetism
Media attachments
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