P4 PART 1

Seite 1

Electrostatics

Electrons transfer from one material to another

Static electricity formed by:rubbing a balloon or comb against insulator (jumper)

Synthetic clothing charged by friction between it and person

Discharging

Earthing

Electrons transferred charged to earth

If charged then earthed electric shock

E.g walking on carpet then touching water pipe

Problems

Dust attracts to TV screen

Dangerous: lightning needs to be earthed so can hit you, a discharge in flour mill causes explosion

Repulsion and Attraction

2 positive or negative repel

2 different attract

Perspex- positive

Ebonite- negative

Becoming charged

Material receives electrons negatively charged

Material loses electrons positively charged

IONS:Atoms and molecules that become charged

Reducing danger

Appliances are correctly earthed

Insulating soles

Insulation mats

Lorries carrying inflammable gases need to be earthed, friction can cause charge, spark can ignite gas

Static in Everyday life

Painting cars:paint neg charged,repel, car lost electrons,pos charged, charges become neutral, even coat of paint

Smoke precipitators:remove smoke from chimneys, metal grid connected to high voltage, makes dust positive, grid negative so attracts, when heavy enough falls to bottom

Defibrillators

Charge to heart

Circuits

Electrons flow from neg to pos electrode normally other way round

Resistance

How hard it is to get a current at a particular voltage through a component

Ohms

Fixed and Variable

Long wire high res low current

Short wire low res high current

Plugs

3 wires:

Live: brown, carries current to applience 230V

Neutral: blue carries current away

Earth: green/yellow stops appliance becoming live

Double insualtion

Conductors have earth wire so cant be live

Insulators don't still have fuse and double inulated

Conductors protect appliance by:short circuits, earth wire has less resistance, fuse wire melts, circuit broken

Fuses and Circuit breakers

Safety devices

Current rating of fuse needs to be above current in appliance

Fuse melts easily

Circuit breaker can reset

Power

Power rating tells us how quickly electrical energy changes forms

Fuses

If fault live and neutral make contact making current flowing higher than rating blowing the fuse

Ultrasound

Cannot hear it

Above 20000Hz

Longitudinal wave

Applications

Used to build internal picture of body

To kill kidney stones- ultrasonic waves vibrate stone, disperses, out with urine

Speed of blood flow

Gall stones

Tumours

Pre-natal scanning

More

Partially reflected at boundary

Time taken for reflections to be detected used to calculate depth of reflecting surface

Advantages

Less harm to cells

Detect tissue

Waves

Rarefaction-far apart

Compression- close together

Wavelength- distance between 2 disturbances

Frequency- number of waves passing certain point in 1 sec

Amplitude-maximum disturbance caused by wave

Particle motion in Waves

Waves transfer energy without moving particles

Longitudinal-particles back and forth

Transverse-particles up and down 90* from direction of wave

Radioactivity

Unstable atoms, decay naturally

Alpha- helium atom, highly ionising, +2 charge, pulls electrons away from atoms making them pos charged

Beta- fast moving electron

Gamma- electromagnetic wave

Number of nuclear decays emitted per sec

Ionisation- atom loses or gains electrons

Alpha Emission

Alpha atom emits alpha particle from nucleus

Makes:

New element

Atomic number decreases by 2

Mass number decreases by 4

2 less protons and neutrons

Beta Emission

Atom decays changes neutron into electron and proton

Makes:

Atomic number increase by 1

1 less neutron, 1 more proton

Half Life

How long it takes for half undecayed nuclei to decay

Igneous Rocks

contain uranium and stable atoms of lead

measure age by: knowing half life of uranium, knowing proportion of uranium to lead

Calculating Halflifes:

Table:find halves in "activity", work out time between them, that is half life

Graph:same as table but on graph

Background Radiation

From: cosmic rays and soil and rocks, hospitals

Tracers

Radioisotopes used as tracers

Tracers used to:see underground pipe leaks, track waste

Gamma put in pipes leaks and blockages detected above ground with tracer

Short half life

Swallowed by patient, spreads through body can see in body (external radiation detector)

Smoke Detectors

Alpha particles cause air particles to ionise, ions are attracted to oppositely charged electrodes causing current

Alpha absorbed by smoke,less ionisation, smaller current sounding alarm

Carbon Dating

Some Carbon and plants and animals is radioactive

Can use carbon 14 to measure how old the dead object is

Dead thing decays carbon 14, doesn't exchange gases

Xrays and Gamma Rays

X rays and gamma rays in electromagnetic spectrum, similar wavelength

Can be used in medicine: X rays can see inside body (radiographer)

Medical isotopes: put material in nuclear reactor, absorb neutrons

X rays made by firing e electrons at metal target

Gamma Rays used to kill tumour (wide beam gamma source rotated around tumour to avoid damage of other cells)and sterilises

Beta used as tracer for short time

Producing electricity

Power stations

burns fossil fuels, heats water, makes steam, powers turbine,

Nuclear power station: uranium is reacted in fission, makes heat, makes steam from water, turbines, powers generators, step up, national grid

Fission

heat released when reactive nucleus splits

Chain reaction:Uranium nucleus absorbs neutron releasing energy, nucleus splits, new neutrons released, new atoms formed

Chain reaction: when more than 1 neutron is released and more nuclei split

Nuclear bomb:fission out of control

Controlling it

Control rods in reactor absorb some neutrons, can raise of lower neutrons preventing danger

Fusion

Heat released when nuclei fuse

Happens in stars

Only at high temperatures and pressures (difficult)

Example:2 hydrogen nuclei fuse to make H-bomb larger nucleus

Cold Fusion (room temp)

Excess energy could be used to replace fossil fuels

Martin Fleischmann and Stanley Pons- may have done it now can't be repeated

Experiments are repeated around the world to check they are correct

May be anomalous results

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