Physics P4
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- Created by: hannahburton
- Created on: 15-04-13 17:52
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 Decay
Radioactive Decay
- 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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Uses of radioisotopes
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
Radiocarbon Dating
- 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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Using Radiation
- 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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