Physics P4

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Static Electricity

Static Electricity is caused by Friction
1) Electrons have a negative charge
2) When two insulating materials are rubbed together, electrons will be scraped off one and dumped on the other.
3) This leaves a positive static charge on one due to a lack of electrons
4) It also leaves a negative static charge on the other due to an excess of electrons
5) Electrically charged objects attract small neutral objects placed near them.

A positive charge never moves only electrons!
a) If enough static charge builds up, it can suddenly ove which can cause sparks or shocks that can be dangerous.

Opposite Charges Attract
Atoms or molecules that become charged are known as ions. Two things with opposite electric charges are attracted to each other.

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More on Static Electricity

Small Problems of Static1) Attracting Dust - Dust particles are charged and will be attracted to anything with the oppsoitve charge.
2) Clothing Clings - When clothes are dragged over each other electrons get scraped off leaving static charges on both parts, this causes small shocks and clothes to stick together
3) Shcks from door handles - charges can build up on your body then when touching metal like door handles or water pipes the charge vlows via the conductor causing a shock.

Static Electricity can be Dangerous
1) A large amount of static charge can build up and cause a spark, if a spark is neear any gaeses or fuel fumes it can cause an explosion.

Objects can be earthed or insulated to prevent sparts by connecting a charged object to the ground using a conductor.

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Uses of Static Electricity

1) Paint Sprayer - bikes and cars are painted using electrostatic paint sprayers, the spray gun is charged, which charges up the small drops of paint. Each paint drop repels all the others, since they've all got the same chage, so you get a very fine spray. For an object to be painted it is given an oppositve charge attracting the charge.
2) Dust precipitators - the smoke in power stations is made up of tiny particles. As smoke particles reach the bottom of the chimney they meet a wire grid with a high voltage negative charge, the dust particles become negatively charged, this is attracted to the positve metal plates which can be changed and cleaned.
3) Defibrilators - pases a charge through the paddles to the patient to make the heart contract.

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Charge in Circuits

Charge Flows around a Circuit
1) Current -  the flow of electrical charge aound a circuit, measured in amps, A. More charge passes around a circuit when a higher current flows.
2) Voltage - is the driving force that pushes the current round, measured in volts, V.
3) Reistance - is anything in the circuit which slows the flow down. Reistance is meansured is ohms
4) There's a balance, the voltage is trying to push the current roudn the circuit, and the resistance is opposing it.

If you increase the voltage - the more current will flow.
If you increase the reistance - then less current will flow

If you break the circuit, the current stops flowing. Current oly flows in a circuit as long as there's a complete loop for it to flow around. Wire fuses and circuit breakers are safety features which cut off a circuit.

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Plugs and Fuses

Wires
Live Wire - brown, carries the voltage
Neutral Wire - blue, completes the circuit, electricity flows in through the live and out through the neutral.
Earth Wire - blue and yellow, this and the fuse are for saftety.

Safety
a) Earthing and Fuses prevent fires and shocks
b) if a surge occurs the current blows the fuse and causes the wire inside the fuse to melt. This cuts off the live supply because it breaks the circuit.
c) This isolates the whole appliance, making it impossible to get an electric shock from the case.
d) it also stops overheating, which could cause a fire.

Formula for electric power: Power = Voltage x current

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Resistance

A resistor is a component that reduces the current flowing in a circuit.

Variable Resitors 1) A variable reistor is a resistor whose reistance can be chagned.
2) They're great for altering the current flowing through a circuit.
Higher resistance - current drops
Lower resistance - higher current
3) The thicker a wire the less resistance

Calculating Resistance
Resistance = voltage / current

You can use a test circuit to measure resistance

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Ultrasound Treatments and Scans

Sound is a Longitudinal Wave1) Sound waves squash up and stretch out the arrangement of particles in material they pass through.
2) Compressions are the bits under high pressure and rarefactions are the parts under low pressure.
3) The wavelength is a full cycle of the wave, e.g from crest to crest
4) Frequency is how many complete waves there are per second, measured in hertz
5) The amplitude tells you how much energy the wave is carrying, or how loud the sound is.
Ultrasound is Sound with a Higher Frequency than we can hear
Uses
1) Breaking down accumaltions in the body - e.g kidney stones
2) For body scanning - e.g baby scans

Advantages over x-rays: ultrasound is good for imaging soft tissue, it's also safe

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Radioactive Decay

Unstable Nucleus1) Radioactive materials are made up of atoms with unstable nuclei that naturally decay at random.
2) As they decay, they give out 3 forms of radiation, alpha, beta and gamma.
3) Gamma radiation happens after a and b emission if the nuclues has some extra energy to get rid of.
Alpha radiation is a  helium nucleus
1) An alpha particle is a helium nucleus, mass 4 and charge of +2, made up of two protons and two neutrons.

Beta radiation is a fast moving electron
A beta particle is a fast-moving electron, with virtually no mass and a charge of -1

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Radioactivity and Half Life

Radioactivitya) Each time an unstable nucleus decays and emits radiation
b) As more unstable nuclei decay, the radioactivity of the source as a whole decreases as a whole drecreases, the older a radioactive source is the less radiation ist emits
c) The time taken for radioactive decay varies between hours and millions of years

Half-Life: Half-Life is the time taken for half of the radioactive nuclei now present ot decay.

A short half means the activity falls quickly, because lots of the nuclei decay in a short time.

A long half-life eans the activity falls more slowly because most of the nuclei don't decay for a long time

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Ionising Radiation

1) Nuclear radiation and x-rays are ionising radiation
2) Some materials absorb radiation it can enter living cells and interact with molecules
3) These interactions cause ionisation, they produce charged particles called ions.
4) Ionisation occurs because the particle gains or loses electrons,
5) X-rays and gamma rays can transfer energy to electrons
6) Lower doses of ionising radiation tend to cause minor damage without killing the cell.
7) Higher doses tend to kill cells completely, which causes radiation sickness if a lot of cells get affected.

Dangerous
a) outside the body, beta and gamma sources are the most dangerous
b) This is because beta and gamma can still get inside to the delicate organs
c) Alpha is much less dangerous because it can't penetrate the skin, inside the body its the most dangerous

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Medical Uses of Radiation

Radiotherapy - Treatment of Cancer
1) Since high doses of gamma rays will kill all living cless, they can be used to treat cancers.

To treat cancer:
a) the gamma rays are focused on the tumour using a wide beam
b) This beam is rotated round the patient with the tumour at the centre
3) This minises the exposure of normal cells to radiation, and so reduces the chances of damaging the rest of the body.

Tracers
1) Certain radioactive isotopes that emit gama radiation can be used as tracers in the body
2) They should have a short half life, around a few hours
3) They can be injected, drunk or eaten
4) These are allowed to spread though the body and their progress can be followed on the outside using a radiation detector.

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Uses of Radiation and Background Radiation

Finding Leaks with Tracers
1) Radioactive isotopes can be used to track the movement of waste materials, find the route of underground pipe systems or detect leaks or blockages in pipes.
2) To check a pipe, insert the radioactive isotope, go along the outside of the pipe with a detector if the reading changes it could be a leak or blockage.

Smoke Detectors
1) A weak alpha radioactive source is placed in the detecor, close to two electrodes, this source causes ionisation of the air particles which allows a current to flow.
2) If there is a fire, then soke particles are hit by the alpha particles instead
3) This causes less ionisation of the air particles, so the current is reduced causing the alarm to sound.

Background radiation comes from many sources such as natural ones, air, food, building materials and in the rocks under our feet. Radiation can  come from space known as cosmic rays and also human activity such as waste from hospitals and industry.

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Radioactive Dating

When organisms die they stop exchanging gases with the air outside and the carbon-14 is trapped inside, and it gradually decays with a half-life of 5730 years. By measuring the proportion of carbon-14 found in some old axe handle, burial shroud, etc, you can calculate how long ago the item was living material using the known half-life.

Dating Rocks
1) Uranium isotopes have very long half-lives and decay via a series of short lived particles to produce stable isotopes of lead.
2) The relative proportions of uranium and ead isotopes in a smaple of rock can therefore be used to date the rock, using the known half-life of the uranium.

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Nuclear Power

Nuclear Fission - Splitting up of uraniu atoms
1) Nuclear power stations are powered by nuclear reactors
2) In a nuclear reactor, a controlled chain reaction takes place in which uranium or plutonum atoms split up and release enerrgy in the form of heat, this is nuclear fission.
3) This heat is then used to heat water to produce steam
4) The steam turns a turbine which drives a generator that produces electricity.

- The splitting of uranium-235 needs neutrons

-You can split more than one atom chain reactions

-Control rods control the chain reaction

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Nuclear Fusion

Nuclear Fusion - the joining of small atomic nuclei
1) Nuclear fusion is the opposite of nuclear fission
2) In nuclear fusion, two light nuclei combine to create a larger nucleus
3) Fusion releases a lot of energy, more than fission
4) Fusion doesn't leave behind much radioactive waste and there's plenty of hyfrogen about to use as fuel.
5) The biggest problems is that fusion only happens at really high presures and temperatures and it requires alot of energy to get these conditions.

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