# Physics P4

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## Sparks - P1

Electrons

• An atom consists if small positively charged nucleus surrounded by an equal number of negatively charged electrons
• In a stable atom, the charge is neutral
• Electrostatics is due to the movement of electrons
• Like charges repel, unlike charges attract
• When a polyethene rod is rubbed with a duster, electrons are transfered into the polyethene, making it negatively charged
• When an acetate rod is rubbed with a duster, electrons are transfered into the duster, making the acetate positively charged
• ATOMS THAT HAVE BECOME CHARGED ARE IONS
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## Sparks - P2

Electrostatic Shocks

• When inflamable gases or vapours are present, or there is a high concentration of oxygen, a spark from static electricity could cause an explosion
• If a person touches something at a high voltage, large amounts of electric charfe may flow through their body to ther earth
• Even small amounts of charge can be fatal
• Electric Shocks can be avoided by...
• Connecting an earth wire
• In a factory, an opperate can stand on an insulating mat, normally made of rubber
• Shoes with insulating soles can be worn
• Anti-static sprays can be purchased. These prevent a build up of charge.
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## Uses of Electrostatics - P1

Dust Precipitators

• Removes harmful particles from the chimneys of factories and powerstations
• A metal grid is placed in the chimney and  is given large charge from a high voltage supply
• Plates inside the chimney are earthed and gain the opposite charge to the grid
• As the dust passes the grid it become charged the same way. Because unlike charges attract, it then sticks to the oppositely charged plates
• At intervals the plates are vibrated so the dust falls into a collector

Paint Spraying

• The spray gun is charged
• All the particles are then charged the same
• The object is given the opposite charge to the paint
• Because unlike charges attract, the paint sticks to the object
• This means the object gets an even coat, with limited paint wasted
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## Uses of Electrostatics - P2

Problems with Paint Spraying

• The object becomes charged from the paint, meaning further paint droplets are repelled away from the object

Defibrillators

• It is a procedure to restore regular heart rhythm through recieving an electric shock
• The paddles are charged from a high voltage supply
• They are then placed on the pacients chest
• Electric charge is passed through the patient
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## Safe Electicals

Live, Neutral and Earth Wires

• Live wire carries high voltage around the house
• The neutral wire completes the circuit
• The earth wire is connected to the base to stop it from becoming live
• A fuse contains a wire which melts if the current is too large
• Earth wires stop a person from recieving an electric shock if they touch a faulty appliance
• A re-set able fuse doesn't need to be replaced to restore power, it can be re-set
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## Resistance and Power

Resistance

• The rheostat changes the resistance
• FOR A FIXED RESISTOR:
• Voltageup,currentup
• FOR A FIXED POWER SUPPLY:
• Resistanceup,currentdown
• Formula for resistance:
• resistance = voltage / current
• MEASURED IN OHMS

Electrical Power

• power= voltage x current
• This can be used to calculate the correct fuse
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## Ultrasound

• Ultrasound is a sound about 20,000Hz which is a higher frequency than humans can hear
• It is a pressure wave containing compressions and refreactions
• compressions are refgions of higher pressure and refractions are regions of lower pressure
• The features of longitudinal sound waves are...
• they can't travel through a vacuum
• The denser the medium, the faster it travels
• the higher the pitch the shorter the wave length
• the more powerful the ultrasound, the more energy the wave carries and the larger the amplitude
• In a longditudinal wave, the virations of the particles are parallel to the direction of the wave
• In a transverse wave, the vibrations of the particles are at right-angles to the direction of the waves
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## Uses of Ultrasound - P1

When ultrasound is used to break-down kidney stones..

• a high-powered ultrasound beam is directed at it
• the ultrasound breaks the stone into smaller pieces
• tiny pieces are then excreted from the body normally
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## Uses of Ultrasound - P2

When ultrasound is used in a body scan...

• At each boundry between different tissues some is reflected and the rest is transmitted
• The different echos mean different body parts
• The returning echos are recorded and used to build up an image

Ultrasound can be used because...

• Different body structures can be calculated using speed= distance / time. Knowing the different speeds helps to build a picture
• It can produce an image of soft tissue
• It doesn't damage cells
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• Radioactive substances decay naturally giving out alpha, beta and gamma particles
• This causes ionisation by removing electrons from other atoms
• This process is random so it's impossible to predict
• The half-life is the average time for half the nuclei present to fade away
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## What is "alpha"?

• Properties
• positively charged
• large mass
• helium nucleus
• has helium gas around it
• During Decay...
• the mass number decreases by 4
• nucleus loses 2 neutrons and 2 protons
• atomic number decrease by 2

<- equation for decay

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## What is "beta"?

• Properties
• negatively charged
• is an electron
• has a very small mass
• travels very fast
• During Decay...
• mass number is unchanged
• nucleus has one more proton
• atomic number increase by 1

<- equation for decay

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Tracers

• When using a tracer to locate a leak in an underground pipe...
• A very small gamma emitter is put into the pipe and dector is passed along the group above the pipe
• An increase in radiation is detected at the leak and no where else after
• Gamma sources are used as they can penetrate the surface

Smoke Detectors

• A smoke dector contains a radioisotope which emmits alpha radiation. Without smoke, the alpha particles ionises the air, which creates current. With smoke, there is no current so the alarm goes off

• Carbon-14 is present in all living things. By measuring the amount, of Carbon-14, the aproximate age can be found. (When something dies, no more of this substance is produced so the amount decreases)
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## Dating Rocks

• Some Rocks Contain Uranium
• This decays leaving a stable isotope of lead
• By comparing the amound of uranium in a rock sample, its approximate age can be found

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• Alpha radiation is absorbed by the skin so is not good for medicine
• Beta passes through the skin and not the bone. It's medical uses are limited.
• Gamma radiation is used in medicine. Cobalt-60 is generally the radioactive substance used to treat cancer
• When nuclear radiation passes through a material it causes ionisation. This increases your risk of cancer
• Cancer cells can be destroyed to exposing the the tumor to large amounts of radiation. This is called radiotherapy
• Materials can be made radioactive  when thier nuclei absorbed extra neutrons in a nuclear reactor

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## Comparing x-rays and gamma rays

• When x-rays pass through the body the tissues absorb some of the radiation. This amount depends on the density of the absorbing material
• Gamma rays have similar wavelengths to x-rays be are produced in different ways
• X-rays are made by firing high-speed electrons by metal targets
• An x-ray machine allows the rate of production and the energy to be controlled, but you can't change this with gamma radiation

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## Treatment

Tracers

• A radioactive tracer is used to investigate inside a patients body without surgery
• Technetium-99m is a commonly used tracer It emmits gamma radiation
• Iodine-123 emmits gamma. It is commonly used to investigate the thyroid gland.
• The radioactive tracer is either mixed with food OR injected into the body
• The progress is monitered through the body by a computer or gamma camera

Treating Cancer

• A radioisotope is used to destroy a tumor in the body
• Three sources of radiation (each with 1/3 of the dose) and placed around the patien twith the tumor at the centre
• This also limits tissue damage
• Radiation is then slowly rotated around the patient, so the tumor recieves constant radiation
• This also means the tissue recieves less of a dose
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## Nuclear Power Stations

• Uranium consists of 2 isotopes uranium-235 and uranium-238
• Enriched uranium is used as a fuel in nuclear powerstations
• Fission occurs when a large unstable nucleus is split up and energy is released
• The heat is used to boil water and produce steam
• The pressure turbs a turbine
• This ritates a generator
• With Uranium fission, a chain reaction occurs
• A nuclear bomb is an example of an uncontrollable one
• In a nuclear powerstation, atoms of uranium-235 are bombarded with neutrons. This causes the nucleus to split an release energy

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## Controlling Nuclear Fission

• the output can be controlled by...
• a graphite moderator can be put between fuel rods to slow down the fast moving neutrons during fission
• Boron control rods can be raised an lowered
• BORON ABSORBS NEUTRONS

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## Fusion

• Nuclear fussion happens when two light nuclei fuse together releasing large amounts of energy
• Requires high tempratures
• Research in this venture is expensive so it is a multi-national venture
• In stars, fusion takes place under high tempratures & pressures
• Fusion bombs are started with a fission reaction which creates a high temprature needed for fusion
• So far attempts to replicate this on earth have been unsuccessful
• Scientists are trying to solve this safely
• Cold Fusion is still not excepted as realisitic since any results are impossible to verify
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