Physics Further

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  • Created by: bethany
  • Created on: 16-05-13 10:42
What is a CT scanner?
it sends x rays through the body area.. Each ROTATIOn provides a THIN slice of the area in great DETAIL
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Whats worse: CT scanner or Xray image capture?
Its a metter of EXPOSURE. Radiation levels could be the same. but CT is moving AXIALLY while scanning it presents LONGER exposure. Single Xray = 1 picture, CT =hundreds
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HOW are xrays used for soft tissue?
A POSITIVE contrast medium ABSORBS xrays more stromgly than tissue, like BArium. They are RADIOPAQUE - appear white. A NEGATIVE contrast medium like CO2 and O2 appear BLACK on radiograph
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Where are xrays on the electromagnetic spectrum?
they have a HIGH frequency and a very SHORT wavelength
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Properties of Xrays?
they AFFECT a photographic film like light does. They are ABSORBED by metal and bone. They are TRANSMITTED by healthy tissue.
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What do Xrays do in medical/practical use?
Form images of bones on photographic film to check for fractures/dental problems. used by historians to check if the art piece is authentic. used at airports - check luggage. Used as xray crystallography - determining structures of crystals.
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What form electronic images of Xrays?
Charged Couplet Devices. - A device for the movement fo electrical charge. - major piece in DIGITAL IMAGING. Its an INTEGRATED circuit with an ARRAY of coupled data manipulated by computer software. they can FORM images of xrays.
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Why are ultrasound distance calculations halved?
Bec ause the time of the pulse involves it returning - so it travels double the distance.
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Distance calculation of an ultrasound?
Distance (m) = Speed (m/s) x Time (s)
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Difference between X rays and Ultrasound?
X rays - ionising, Ultrsound - non ionising. Ultrasound uses soundwaves - safer. Both are cheap and quick, unless MRI or CT scan - great imaging, but radiation =bad. Ultrasound - vibrations
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Purpose of xrays and ultrasound
both view the body without cutting it open.
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Magnetic resonance imaging (MRI)
It uses strong magnetic fields and radio waves to produce detailed images of the inside of the body. An MRI scanner is a large tube that contains a series of powerful magnets. You lie inside the tube during the scan.
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Whats better Xrays, Ultrasound or MRI?
MRI and ultrasound - no exposure to ioninsing raditaion
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Disadvantage of MRI
If you have a pacemaker - it is a danger.
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What can normal ears hear?
20Hz - 20KHz
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how are ultrasounds measured?
Electronic systems produce these ultrasound waves. When the wave MEETS a BOUNDARY part of it is REFLECTED back. which travels back to the detector.
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How can you protect exposure to Xrays?
Wear a film badge - monitor exposure to ionisng radiation - a cumulative radiation detector. And MAXIMISE your DISTANCE. and wear a LEAD APRON - shields you / ABSORBS x rays
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What are ultrasounds used for?
SHATTER kidney stones, guiding CATHETERS into vessels, MONITOR newborn babay, SOFT tissue - like eye
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What is refraction?
change of direction of light as it enters a medium where the speed is different, passes from a transparents substance for example
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TAG AGA
towards the normal air to glass - away from normal glass to air
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how are x rays ionising? (general)
They enter the body and DEPOSIT ENERGY by IONISING an ATOM.
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how are x rays ionising (genetic)
they DISRUPT DNA chains,which may BREAK them completely, or make them REPAIR incorectly - this leads to CANCER CELL MUTATIONS.
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how are x rays ionising (water)
if it ionises a WATER MOLECULE, you have a CHARGED HO and H atom. These combine and make CHEMICAL changes which is like a form of BLEACH molecule formed.
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what is the refractive index?
how much a subtacne can refract a ray of light
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caluclation for refractive index
N = sini/sinr i (incidence) r (refraction) n (refractive index)
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when is light not refracted?
when is travels along the normal
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How does endoscopy work?
1)flexible tube inserted through natural opening (mouth). 2) A light source outside the body illuminates the optical fibres. 3) a lens systems is used. 4) an eyepiece is used
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AN endoscope involves what reflection?
total internal reflection
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when is total internal reflection occured?
when the angle of incidence is greater than the critical angle
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what is an optical fibre?
a very thin flexible glass fibre
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How to work out the critical angle?
the critical angle is the incidence angle. This is done by: N(refractive index) = 1/sin c (critical angle)
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What is a moment?
the turning effect of a force
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formula for moment
M(nm)= F (n)xD(m) - PERPENDICULAR DISTANCE from LINE OF ACTIOn to the PIVOT
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How to increase the moment?
increase force or increase distance
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What does a lever do?
acts as a force multiplier, the FORCE exerted=EFFORT, the force we try to move is the LOAD
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What is the centre of mass?
the point of an object where its MASS is THOUGHT to be CONCENTRATED
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what is known when an object is freely suspended?
it rests, and the CENTER of mass is directly BENEATH the point of SUSPENSIon. it is at EQUILIBRIUM.
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How to measure the centre of mass?
suspend it from a clamp stand, and hang a plumbline from the first point of the object, then repeat 2 times. Where they cross is the centre of mass
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Where is the cenrte of mass of a symmetrical object?
along the axis of symmetry
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What is the calculation for an object at equilibrium? (moments)
sum of clockwise moments about that point =sum of anticlockwise moments about any point
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Examples of PRINCIPLE OF MOMENTS:
see saw, balance scale
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What is stability of an object?
where the line of action of the weight acts through the centre of mass
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Why will an object topple?
if the line of action of its weight is outside the base. If the resultant moments is NOT ZERO
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How to increase stability?
wider base, lower centre of mass
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What does a hydraulic system do?
it uses pressure in a fluid to exert a force - force multplier, a SMALL EFFORT can move a LARGE LOAD
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what does pressure in a fluid do?
acts equally in all directions, they are virtually INCOMPRESSIBLE
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calculation for hydraulics?
P(pressure pascals) = Force (n)/ A (area) m2
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What does hydraulic pressure depend on?
the force exerted, both areas
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what is centripetal acceleration?
when an object moves in a circle. It continuosly changes direction. so it CONTINUOULSY CHANGES VELOCITY. so - it accelerates.
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what does a centripetal force depend on?
mass of object increased, speed increased, radius DECREASED
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An object only accelerates when a resultant force acts on it, the force that keeps this object moving in a circle is called?
centripetal force
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what happens if the centripetal force stops working?
the object moves in a STRAIGHT LINE, at a TANGENt to the circle
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what force provides centripetal force? examples
gravitational force, tension, electric force
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what is a pendulum an example of?
oscillating motion
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how to measure the time for a pendulum oscillation?
measyre the time for 20 then divide by 20
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what does the time period of a pendulum rely on? and how calculated
its length, it is a complete CYCLE. from the highest point at one side to the highest of the other and back to start
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why do swings stop oscillating?
friction at top of swing and air resistance
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what does a simple pendulum consist of?
a mass called a BOB, suspended on the end of STRING. when it is DISPLACED and let go at one side, it will OSCILLATE. THROUGH the equilibrium position.
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what is the amplitude of a pendulum?
the distance from the equilibrium to its highest point of oscillation
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what is the frequency of a pendulum? and calculationb for the time
the number of oscillations in 1 second; T(s) = 1/F (hz)
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What does an electromagnet consist of?
a coil of insulated wire wrapped around an IRON CORE
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what are elctromagnets used in?
circuit breakers, relays, cranes
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what is magnetic field?
the area of influence exerted by the magnet force
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what are magnetic field lines/line of force
they are shown as continous by displacement of iron filings, and like the contour lines that show the magnetic patterns
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why are electromagnets more use?
They can be switched on and off. The strength of the magnetic field can be changed, by altering the current. They are TEMPORARY
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The magnetic field around a coil electromagnet can be increased by:
Increasing the current in the wire. Putting more loops on the coil Placing an iron or steel core inside of the coil.
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how is a electromaggnet made?
by wrapping insulated wire around an IRON CORE. when the current flows through the wire, the iron becomes strongly magnetised. when the power is switched off, it loses its magnetism.
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what is the motor effect?
If a wire carrying a current is placed in a magnetic field a force is produced.
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flemings left hand rule?
first finger - magnetic FIELD. second finger - CURRENT. ThuMb - DIRECTION of force
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when if force of motor effect increased
increased by the current /strength of magnetic field is increased
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split ring commutator?
it reverses the direction of the current around the coil every half turn, because the sides then swap over every half-turn, the coil is always pushed in the same direction.
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If the ends of the coil in the motor are parallel to the magnetic field , thesize of the force is...
zero
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Other cards in this set

Card 2

Front

Whats worse: CT scanner or Xray image capture?

Back

Its a metter of EXPOSURE. Radiation levels could be the same. but CT is moving AXIALLY while scanning it presents LONGER exposure. Single Xray = 1 picture, CT =hundreds

Card 3

Front

HOW are xrays used for soft tissue?

Back

Preview of the front of card 3

Card 4

Front

Where are xrays on the electromagnetic spectrum?

Back

Preview of the front of card 4

Card 5

Front

Properties of Xrays?

Back

Preview of the front of card 5
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