Physics unit 3

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  • Created by: Michaela
  • Created on: 26-05-13 07:12

Radiation in medicine

Key terms:

  • Radiation:
  • Diagnosis:Identifying a medical condition by its signs and symptoms or from a medical imaging scan.
  • Endoscope:a tube that can be inserted into the body.It uses total internal reflection in optical fibres to send light into the body and reflect a picture back of what is inside
  • CAT Scanner:an x-ray picture that shows a slice through the body
  • Ultrasound:
  • Ionising:radiation that can cause charged particles to be formed by knocking outer electrons form the outer shell or giving them enough energy to break free from the atom.causes tissue damage and mutations
  • Non-ionising:radiation that does not cause charged particles to be formed
  • intensity:the strength of a wave defined as power of incident radiation/area
  • medium:material though which electromagnetic waves travel through.
  • incident:falling or striking radiation on something
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Radiation in medicine

Visible light

Light reflects off features to form an image



x-rays are absorbed by some materials and not others. A negative image is produced

x-ray photography and CAT scanners

Gamma Rays

The movement of substances producing gamma rays is detected and the positions are shown on a screen

PET scanner-a medical scanning technique. The image of metabolic active sites inside the body is computerized by detecting gamma rays coming from positron -electron annihilation

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Radiation in medicine and how eyes work

Intensity is the power of incming beam od radiation -called the incident of radiation.

Intensity( W/m) = power of incient of radiation (W)/area (m)


How eyes work

  • cornea:outer transparent layer of the that refracts light entering the eye
  • pupils: the round hole in the centre of the cab change size in response to changes in light
  • lens: further converges light rays which have been refracted by the cornea to focus on the retina
  • retina:tissue at the back of the eye that contains light receptors
  • iris: coloured ring around the eye that controls the size of the pupil and hence controls how much light enters the eye
  • converge:bring closer together
  • refracting:the change in direction of a wave due to a change in wave speed at an interface between 2 media
  • ciliary muscles: muscles that relax or contract to change the shape of the lens in the eye
  • far point:the furthest point at which the eye can focus
  • near point:the closest point in front of the eyes that an object may be clearly focused-25cm
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How the eye works


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How the eye works

  • the light enters the eye through the pupil
  • the light rays pass through the cornea and the lens before reaching the retina at the back of the eye
  • the image formed is converted into electrical impulses by the cells in the retina and neurones carry them to the brain which interprets them.
  • dilated PUPIL: the pupil is large
  • constricted pupil:the pupil is small
  • To from a sharp image on the retina light rays must converge on the retina. The path of light has to be changed in the eye-refracting
  • refraction is done  by the cornea and partly by the lens.
  • If the object being viewed is nearer or further away the shape of the lens is controlled by ciliary muscle in order to keep the image in focus
  • Far object: the light rays are parallel and are refracted by the cornea and the lens-ciliary muscle relax making the ring of muscle wide and so pulling the lens into a thinner shape.
  • Near object: ciliary muscle are contracted making this ring of muscle smaller and so allowing the lens to relax into a fatter shape.
  • When the iris becomes smaller the pupil widens and lets mor light in
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Sight Problems

  • short sight:eye sight problem when someone can see nearby object but cannot focus clearly on far away objects.caused by the light rays being focused to the point in front of the retina
  • long sight:eye sight problem when someone can see objects far away but cannot focus on near objects-caused by light rays being focused to a point behind the retina .
  • diverging lens: a lens that spreads out light rays
  • converging lens: a lens that brings light rays together
  • laser correction:using a laser to permanently reshape the curvature of the cornea so thatt he focal length of the eye is changed
  • The cilary muscle make the lens shorter and fatter for near objects and relax to make a thinner lens for distant objects so that the rays of light meet on the retina.

Shot sight

  • eyeball too long or the cornea being curved to sharply-focused in front of the retina

Long light

  • eyeball too Short or the lens not being thick or curved enough-cilary muscle are taut **** the lens cant bend light
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Radiation in medicine

Ultra sound

High frequency sound waves that reflect off features inside the body to form an image

Ultrasound scanner

  • lasers are used in eye surgery to correct vision defects-visible light (ni)
  • absorption of ultrasounds used to treat swollen tissue (ni)
  • gamma rays and x-rays can be used to damage or destroy caner cells (i)
  • The intensity of the radiation decreases the further away from the source
  • Intenisty is also affected by the medium-the denser the medium the weaker the radiation gets
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Correcting vision

Short sight: wearing glasses with diverging lens which bends incoming rays apart so that the cornea and lens can focus the rays correctly onto the retina

Long sight: wearing glasses with convering lenses which refracts the rays more so that the meet on the retina

An alternative is placing a contact lens in front of the cornea- must be soft and allow oxygen to permeate to the eye. To prevent infection it is important that the lenses are cleaned regularly.

Laser correction surgery: uses laser to shape the front of the can amke precsie incisions wihtout damaging the surrounding area .

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Different lenses

Converging lens: parallel light rays are refracted to meet at the focal point. the distance between the lens and the focla point is the focla length.


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Different lenses

Diverging lens: the focal point is the point from which the rays seem to be coming after passing through the lens.A more powerful divering lens will have a more sharply curved faces and cause the rays to diverge moreso the focal length is shorter(

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Different lenses

  • the power of a lens (a measure of how much a lens refracts light rays, related to its shape measure in dioptres-diverging lenses have a negative power) is measure in dioptres and calculated from its focal length: a lens with a focal length of one metre has power of one dioptre (unit if power for a lens)

POWER OF LENS ( dioptres D) = 1 / FOCAL LENGTH (metre ,m)


  • An image will only form at the same distance as the focal length if the incident rays are parallel.when rays are not parallel the lens equation links the object distance, the image distance and focal length to form either a real or virtual image.
  • u=oject distance
  • f=focal length
  • v= image distance

1/f= 1/u + 1/v

use the same unit for all variable

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lens equation

  • Real image:an image that can be projected onto a screen ( normal converging lens)
  • real is positive sign convention: convention for the lens equation that real images have a positive image distance and distances measured from the other side of lens are not negative
  • Virtual Image:an image that cannot be projected onto the screen (diverging lens and have a negative value)
  • Images to the right of the lens are real and the distance between the image and the lens are positive.
  • Those to the left of the lens are virtual and v is negative
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Reflection and Refraction

  • reflected:when a wave or ray or particle bounces off a surface
  • law of reflection: the angle of incidence equals the angle of reflection for a wave or a ray at the surface
  • angle of incidnce: the angle between the normal and the wave or ray when it hits the surface
  • angle of reflection: the angle between the normal and the reflected wave or ray when it leaves the surface
  • Snell's law:a law for the refraction of light rays or any type of wave, which states that when a wave passes through one medium to another the ration of the sine angle of incidence tot he sine angle of refraction is constant
  • refractive index: the ratio of the speed of light in a vacuum to the speed of light in a particular material
  • norma: an imaginary line drawn at right angles to the surface of the mirror or lens where the ray of light hits it.

Law of reflection

  • angle of incidence =angle of reflection
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Reflection and Refraction



  • when waves enter a medium in which they travel more slowly the direction changes
  • rays are refracted towards the normal when they enter a medium in which they travel more slowly.
  • Rays are refracted from the normal when they enter a meduim in which they travel faster.
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( light slows down and refracts towards the normal. In glass to air the light speeds up refracts away form the normal.

  • when a wave enters a medium where the the speed decreases the part still moving at the higher speed catches up with the part slowing down-this alters the waves direction of travel.
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Snell's law

For waves passing from one medium to another Snell's law links the angle of incidence and the angle of refraction.

sin i/sinr =constant.

the constant in Snell's law is related to the refractive index,n, of each material.

sini/sinr = nr/ ni

where ni is the refractive index of the medium the ray is travelling from and nr si the refactive index of the medium the ray is travelling into.

the angle of refraction depends on how different the refractive indices of the 2 material are.

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Critical Angle

  • Critical angle:the smallest angle of incidence at which the angle of refraction is 90 or total internal reflection occurs
  • Total internal reflection: when all of a wave is reflected from a boundary instead of refracted. occurs when the angle of incidence is greater than the critical angle (90)
  • when a wave enters a medium where it travels faster the angle of refraction decreases and so does the angle of incidence.
  • at angle less than the critical angle some of the ray is reflected and refracted-partial refection refraction.
  • As the angle of incidence decrases the more refaction there is and less reflection.
  • when light rays pass into a medium in which the travel faster-the ray of light will travel along the boundary.

Uses: many cars have automatic rain sensors which turn o windscreen wipers-relies on total internal reflection.

  • An infrared source inside the car directs a beam to the windscreen the beam travel through the windscreen and reached the boundary between the air and glass at an angle that is grater that the critical angle-total internal refection occurs.
  • However when it rains, the water on the glass allows some of the beam to br refracted so less reaches the detector ,signalling the windscreen wipers.
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Critical Angle


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Calculation of critical angle

  • Snell's law can be applied to the light approaching the edge of the medium at the critical angle,c.
  • The critical angle travels along the boundry so the angle  fo refraction is 90.

sin c/ sinr = nr/ ni

  • in this case r= 90 and sin is 90 =1
  • for light entering air from glass or water the refractive index of air is 1


sinc = 1/ ni

this shows that the greater the refractive index,the smaller the critcal angle.if the angle on incidence is greater than c then sin r would have to be greater than 1 to obey Snell's law.

no angle has a sine value of more than 1

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Using reflection and refraction

  • Total Internal reflection : used in optical fibres (tight bundle of glass fibres which transmit form on end to the other by total internal reflection) which transmit visible and infrared waves for telephone,TV and other data communication.
  • Optical fibres are used in endoscopes to enable surgeons to examine the inside of a patient , therefore it is non-invasive .
  • It consists of flexible optical fibres some of which carry light.Light is reflected off the inside of the body, which is then gathered and focused by an eye piece lens to form a clear image of the inside of the body.

Ultrasound:sound waves with a high frequency above 20 000 Hz,which is too high for the human ear to detect

  • they travel through solid objects but are partially reflected when they enter a different medium.Used in medical scanning and the same device both transmits and receives ultrasound.
  • Th waves travel tjrough the body and are refelcted at interface between differnt tissue.
  • Used for both diagnosis and treatment eg. it can help to locate kidney stones and then the high intensity ultrasound can be used to break up the stone when it absorbs th energy.
  • Absorption of ultrasound can also be used in physio to treat injured muscles-the ultrasound can be focused and its intensity controlled so the energy can be directed effectively.
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  • X-Rays:electromagnetic wave with high frequency and high energy.ionising radiation
  • Evacuated tube:a tube from which the air has been removed so that there is a vacuum
  • filament:a thin wire.In thermionic emission a heated filament emits electrons and forms the cathode when current is passed through the evacuated tube
  • electron gun: heated cathode that emits electrons,and the apparatus focuses the beam of electrons
  • thermionic emission:the process of emitting an electron from the surface of a heated metal,usually a hot filament.
  • potential difference: aka. is the difference in energy carried by electrons before and after they have flowed through a component.

The more energy x-rays have the more ionisng they are-the energy of an x-ray is related to its frequency.

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X-ray machine:

  • consists of an evacuated tube that contains 2 electrodes.
  • The cathode is a wire filament-when heated it becomes the electron gun and emits electron-thermionic emission.
  • If there is a large potential difference the electrons are accelerated to the anode.
  • The tube is evacauted so taht the elctrons do not collide with other particles.
  • The anode is made out of metal-electrons collide and slow down very quickly.
  • Most of the  kinetic energy is converted into thermal but some is converted into x-rays.
  • higher potential difference will produce x-rays with greater energy.

Comparing Currnet:

  • charged particles flow from the cathode to the anode completing the circuit.
  • the movement of charged particle is equivalent to an electric current.
  • If temperature of the cathode is increased the number of electrons emitted increases and so x-rays produced increases.

I=N x q ( I =current ,N = number of particles flowing , q =charge on each particle in coulombs)

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Kinetic Energy


kinetic energy = 1/2 mv2

m= is mass of electron in kg

v-is velocity of electron in m/s

Also expressed as:

kinetic energy = eV

where e = the charge on an electron ,1.6x 10-19 C

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Using x-rays

  • When x-rays are emitted it spreads out and the strength decreases as it gets further away from the source-when you double the distance form the source the strength decreases to a quarter-inverse law: value of physical quantity is inversely proportional to the square of the distance from the source pf the physical quantity

Absorption of x-rays

  • the denser the material the more x-rays it absorbs eg. bone is denser than tissue and therefore absorbs more x-rays.Dark areas-  a lot of detection but little of absorption of x-rays. Light areas- a lot absorption of x-rays and little detection.

CAT Scans and Fluoroscopes:

  • CAT Scans -the x-ray source is moved around the patient in a circle-detectors are positioned on opposite ends to the sources-the x-rays detected are used build corss sectional views of the body- sometimes made into 3D. Used to diagnose many types of caner
  • Fluoroscopes:a device that uses x-rays and a fluorescent screen to obtain moving picture of inside the body eg. used to detect blocked blood vessels.Patient is placed between the x-ray source and the detector
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Risks and Benefits of CAT Scans and Fluroscopes

  • Both are painless and non-invasive.
  • eliminate the need for a biopsy.
  • help to decide what the traement should be.
  • Give the patient a dose of radiation that is = to 10 years of background radiation.
  • increases the risk of developing cancer-not recommended to pregnant women and children.
  • Risk is reduced by firing x-rays from several direction so that only the tumor receives a high dose.
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ECGs and Pulse Oximetry

  • When a heart beats each cell must contract at the same time  in order for the blood to be pumped out-an action potential(change in voltage across a neurone or membrane of cardiac muscle cell when an electrical signal passes along it) is snet in oredr for this to happen
  • the body has a large amount of water and salt-conducts electricity well-action potential travel through the body to the skin where they can be detected.
  • Electrocardiogram(ECG)- a graph showing the change is voltage produced by the heart, used to monitor heart action.
  • When the heart is beating normally there is a regular pattern-you can work out heart rate and abnormalities in the heart from an ECGS.
  • The horizontal scale is usually 0.2 seconds for each larger square

Frequency(f ,hertz) = 1/ time period (T seconds)

  • time period:the time taken for one cycle of a regularly repeating event.
  • the frquency of the HB is given as beats oer minute- frequency x 60 =number beats per minute or HR.
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Pulse Oximetry and Pacemakers

  • Pulse Oximetry: using a pulse oximeter to measure the pulse rate and the amount of oxygen in the blood
  • Pulse Oximeter:device placed on the surface of the body that uses LEDs and light detector to measure the amount of oxygen in the blood form how much infrared is absorbed and measure the heart rate from the interval between the peaks in infrared absorbance.
  • Each beat of the heart causes a surge of oxygenated blood-absorbs more infrared than deoxygenated blood-by comparing the absorbance between the 2 LEDS it can work how much oxygen is presnet.
  • Oxygenated blood: some red light passes through and little infrared passes through.
  • Deoxygenated blood: less red light passes though and more infrared passes through.

Pacemakers :a device which helps the heart to beat properly by detecting the action potentials and applying electric signals to regulate the heart action.

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Beta and Positron emission

  • Protons:positive particle mass of 1 and is made of 2 up quarks and 1 down quarks
  • neutrons:particle with 0 charge and mass of 1 and is made of an1 up quark and 2 down quarks
  • electrons:a negatively charged particle that has a negligible mass
  • Protons and electrons are equal -atom has no charge and protons and neutrons are referred to as nucleons(particle found in the nucleus)
  • proton or atomic number-no. of protons bottom no.
  • Mass number or nucleon no. is the no. of protons and neutrons-top number.

Beta decay: the emission of a positron or electron.

Beta minus decay:radioactive decay in which a neutron becomes a proton which remains in the nucleus and an electron is emitted form the nucleus. 1 down quark turns into and up quark

  • beta partcle:high kinetic energy electrons or posirtons(+) emitted as ionisng radiation froms some isotopes
  • position:the anti-particle of an electron having the same mass but the opposite charge.
  • Radiation able to penetrate paper but not metal.
  • increases the atomic number by one but leaves the mass number unaffected.
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Beta and Positron emission and alpa emission and G

Beta + decay:radioactive decay in which a neutron becomes a proton which remains in the nucleus and a positron is released.1 up quark changes into a down quark.

  • decreases the atomic 1 but leaves the mass no. unchanged

Alpha radiation: not very penetrating but are very ionizing -massive compared to beta particle and can easily dislodge and electron from any atom they collide with-means they soon lose energy and have limited rage.

  • Alpha particle: particle made up of 2 protons and2 neutrons emitted as ionising radiation from some types of isotopes
  • Alpha decay:emission of an alpha particle from a radioactive isotopes
  • results in the atomic no. decreasing by 2 and the mass no. decreasing by 4.

Gamma Radiation:ionising radiation in the form of pulses of electromagnetic radiation with very short wavelengths

  • waves that are very penetrating but not very ionising.
  • results in no change to atom.
  • When gamma rays are released the nucleus loses energy and therefore become more stable

Neutron Radiation: radioactive decay sometimes results in a neutron being ejected-neutrons have no charge and so are not directly ionising but they are penetrating

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Nuclear Reactions and the Stability curve

Nuclear Reaction

  • Nuclear equation: equation representing a nuclear recation
  • alpha particle ( helium nucleus) is shown as :
  • an electon is show as:
  • a positron is shown as:
  • a gamma ray has zero mass and zero charge:

The stability Curve: N-Z curve is a line on a graph of the number of neutrons (N) against the no.of protons (Z) for all isotopes of different elements showing the stable isotopes.Isotopes above the the curve have too many neutrons - B- decay.Isotopes below the curve have too many protons and undergo B+ decay.

  • isotopes: have the same protons but different numbers of neutrons
  • stable:unlikely to decay
  • Unstable:likely to decay
  • decay:the process of transforming to another element or isotope when radioactive isotopes emit ionising radiation
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The Stability curve

  • lighter elements appears in the bottom left corner and heavier element towards the top right.
  • N-Z curve show the stable isotopes - dark dots- line stops at 82 because above this all isotopes are unstable.
  • Isotopes above the N-Z curve have too many neutrons to be stable - B - decay.
  • Isotopes below the N-Z curve but close to it have too many protons -B+ Decay.
  • Radioactive Isotopes:unstable isotopes that emits radiation as alpha particles ,beta particle or gamma rays
  • Elements at the top undergo alpha decay
  • elements near the bottom -neutron decay
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Quarks: particle form which protons and neutrons are made which each contain 3  quarks,


  • mass:1/3
  • charge:+2/3


  • mass:1/3
  • charge:-1/3

Proton: 2 up quarks and 1 down quark 

  • u+u+d =p
  • +2/3 -1/3 + 2/3 = +1

Neutron: 2 down quarks and 1 up quark

  • d+d+u=n
  • -1/3 +2/3 -1/3 =0
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Quarks and Beta decay

B- Decay :neutron becomes proton and an electron is emitted

  • down quark changes to up quark
  • -1/3 = +2/3 ----- -3/3 = -1e
  • neutron---proton +electron
  • udd-----uud 

B + Decay: Proton changes into neutron and positron is emitted

  • up quark to down quark
  • + 2/3 + -1/3 ------- +3/3 = +1e
  • proton-----neutron + B+
  • uud------udd +positron
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Dangers of Ionising radiation

  • Radiation may kill cells or stimulate the growth cancer cells.
  • Risk to their living cells and the DNA-radiation can cause mutation:a change in the base sequence of DNA- can cause harmful adaptions that are passed onto the next generation
  • Radiation can cause burs depending on the exposure and the type of source.
  • Beta burns look like sunburns and gamma burns extend deeper.
  • Medical staff working with radioactive sources have to limit their exposure by:
  • increasing their distance.
  • shielding 
  • containment of the source
  • Some patient use radiation for their treatment but dosage is controlled
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Radiation in hospitals

  • Radiotherapy:
  • Radiotherapy may used for palliative care(a medical intervention that does not cure a condition but may reduce pain or other symptoms) shrinking tumors -condition wont be cured but patient will be in less pain and better quality of life.


  • Cancers can be diagnosed using a tracer (a radioactive substance that is injected into the body and emits gamma rays that can be detected outside the body to monitor how a part of the body is doing)it is usually a substance used by the body eg. glucose made from atoms from a specific radioactive substance.
  • Some isotopes such as iodine can be aborbed directly by the body and does not need to be incorporated into a larger molecule.
  • The isotope must have a short half life so that other parts of the body are not affected.
  • The patient is injected or breathes in the tracer and is then given a PET scan to locate tracer.
  • Isotopes have short half life so they are made close to where they will be used.
  • The tracer emits a positron,which collides with an electron releasing 2 gamma rays in opposite directions which are detected by a PET camera
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Collaboration and Circular motion

Key words

  • particle physics:the study of sub-atomic and fundamental constituents of matter
  • sub atomic particles:
  • fundamental particles: a particle that can't be broken down into smaller units.Quarks and their anti particles are thought to be fundamental
  • particle accelerator:device used to accelerate charged particles at very high speeds.Using particle accelerators it is possible  for particle physics to collide particles at high energies and trough this to break down matter into smaller particles.

Particle physics helps to build an picture of the properties of sub-atomic.p. New models and theories are tested over time by other scientists who repeat the experiment and critically evaluate the work published in scientific journals.


  • large collaborations allow the high cost to be spread.
  • Brings together the expertise of many people from around the world
  • increases international relations
  • Could cause conflict due to different ideas
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Circular Motion and Accelerators

  • The LHC is a particle accelerator.

Circular Motion.

  • resultant force:the total force that results from 2 or more forces acting on a single object.It is found by adding the forces together ,taking into account the directions
  • centripetal force:resultant force is needed for the circular motion in an inwards direction,towards the centre of the circle.Because the direction of motion is constantly chaging the object is accelerating even though the speed does not change
  • eg. hammer throwing- to keep the hammer moving a resultant force is acting inwards along the radius is needed-centripetal force. The centripetal force for the hammer is provided by the the tension in the wire.When it is released there is no longer a centripetal force and it travel in a straight line at a tangent to the circular path it has been following.

Cyclotrons:type of partcle accelerator which uses a magnetic field to cause charged particles to travel in a circular path and also increase their speed.

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  • A constant magnetic field applied at right angles to the particles motion produces the centripetal force required.
  • A voltage is applied across the 2 D Shaped magnetic fields which accelerates the charged particles.
  • The path spirals outwards as speed increases.
  • On leaving the magnetic field the particles travel in a straight line towards a specific target.In LHC this is another particle.
  • If the high energy particle is allowed to collide with a stable element,the nucleus can be changed into an unstable isotope.
  • Small Cyclotrons are used in hospitals to produce short -lived isotopes needed for PET Scans- medical scanning technique.The image of metabolically active sites inside the body is computerised by detecting gamma rays coming form positron-electron annihilation
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  • Colliding objects have kinetic energy and momentum,which is a measure of the strength of movement (momentum=mass x velocity) 
  • Momentum is conserved in all collisions
  • Inelastic collision: a collision where the kinetic energy is not conserved.Soem of the kinetic energy is transferred to the surroundings.
  • Elastic collision:a collision where there is conservation of kinetic energy
  • Momentum (measure of motion) is a vector( a physical quantity that has both magnitude and direction) and has both size and direction 

Working out mass conservation :  using v to calculate the speed of the car after collision

  • Momentum of object = mass x velocity
  • Total momentum before =( 500 x5) + ( 400 x2) = 3300 kgm/s
  • Total mometum after collision= ( 500 x 3)+ (400 x v)
  • Momentum is always conserved in collisions so:
  • 3300=1500+400 x v
  • v= 1800 / 400
  • v = 4.5 m/s 
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PET Scanners

  • When an electron and a positron collide annihilation ( the total destruction of matter.In the context of matter and anti matter particles this means the destruction of the masses of the particles involved,turning their masses into energy )occurs and 2 gamma rays are produced moving in the opposite directions
  • Mass Equivalence : the idea that the mass of a body can be inter changed with energy.this means that energy can appear through the disappearance of mass such as when a positron and electron annihilate and 2 gamma rays are produced.The equivalence is described by  E= mc2 ,where E is energy,m is mass and c is the speed of light in a vacuum.
  • We say that mass energy has been conserved
  • The positron and election approach each other with the same speed meaning they have equal but opposite momentum so their momentum before the collision is 0. Although gamma rays have no mass they have energy-which mass is equivalent to- so the gamma rays have momentum.So for the total momentum after the collision to be 0 2 gamma rays of the same energy must be produced, moving in opposite direction.
  • Charge before and after is 0 - hence charge is also conserved after collision
  • E= mc 2 : E - energy , m-mass and c- speed of light in a vacuum = 3 x 10 8 ms -1
  • mass of an electron is 9 x 10 -31 so its energy is = 9 x 10 -31 x ( 3 x 10 8) 2 = 8 x 10 -14 J.
  • a positron has the same mass as an electron so total energy released by annihilation= 1.6 x -13 and the energy of the 2 gamma rays are equivalent.
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Positron emission tomography (PET) scanners

  • During a PET scan the annihilation of positron and electron is used to make gamma ray pair that enables an internal image of the body to be formed.
  • Radio isotopes are injected in the blood in a tracer and the tracer accumulates in various tissue.
  • The positron in the isotope only travel a short distance before they collide with an electron-annihilation take place and gamma ray pairs are produced and detected by sensors positioned around the patient
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Kinetic Theory

  • Kinetic theory:the theory explains the different states of matter in terms of movement of particles
  • Kinetic energy: The energy that a particle has due to its movement ( KE = 1/2 x m x v2)
  • Solids:held together by strong forces and can only vibrate
  • Liquids: bonds not quite strong and particles can slide past each other-usually incompressible
  • Gas: particles are far apart and able to move freely/ compressible and expand to fill a container.Temp of gas is measured by average kinetic energy/ faster the average speed the higher the temperature.

Particle and pressure

  • pressure:the force on a certain area measured in pascal or N/m2
  • pascals (Pa): a unit of pressure. 1Pa = 1 N/m 2
  • the pressure of a gas is caused by the forces exerted as the moving particles hit the wall of the container.
  • The faster the particles are moving ,the more collisions occur and the more force that will be exerted on the wall of container.
  • Increasing the temperature and concentration increases the pressure- units are Pa or N/m2
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Absolute Zero

Absolute zero

  • Absolute zero: the temperature at which the pressure of gas drops to 0 .It is -273 C or 0 K
  • Kelvin temperature scale: A temperature scale that measures temperatures relative to absolute 0
  • Kelvin (K): the unit of kelvin temperature scale.1 kelvin is the same temperature interval as 1 C
  • It is the temperature at which pressure would be zero and there would be no particle movement.



The average kinetic energy of particles in a gas are directly proportional to the to the kelvin temperature of gas.

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Calculating Volumes and Pressures

  • Gases take up large amount of space at atmospheric pressure they need to be compressed and stored at higher pressure in order to put them into takes .eg oxygen for hospitals.
  • If the volume of a gas inceases at a constant temp, the pressure decreases
  • V1P1 = V2P2
  • v1 and v2 are volumes in m3 and P1 and P2 are pressure in pascals
  • if the temperature if gas is increased at a constant pressure the volume increases.
  • V1 = V2T1/T2
  • T is temperatures in Kelvin
  • Combining the Equation
  • nitial pressure (pascal, Pa) x initial volume (metre3m3/ initial temperature (kelvin, K) = final pressure (pascal, Pax final volume (metre3m3/ final temperature (kelvin, K)
    • P1V1/T1 = P2V2/T2
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