P4 - radiation for life

• Two insulating materials are rubbed together electrons will be scraped off one and dumped on the other
• positive static charge on one due to a lack of electrons - lost electrons leaving a positive charge 
• negative static charge on the other due to an excess of electrons - gained electrons 
• electrically charged object attract small neutral objects 

• polythene rod, electrons move from the duster to the rod 
• acetate rods, electrons move from the rod to the dusters 

being a nuisance:

• attracting dust: dust particle are charged and will be attracted to anything with the opposite charge. object around the house easily get charged and attract the dust particles.
• clothing clings and crackles: synthetic clothes are dragged over each other, electrons get scraed off, leaving static charges and lead to attraction and little shocks as the charge rearrange themselves
• shocks from the door handle: on nylon carpet while wearing insluting shoes, charges build up on the body. charge flows via the conductor and you get a shock when touching metal.

dangerous:

• static charge can build up on clothes. this charge become large enough to make a spark 
• as fuel flows out of a filler pipe, or paper drags over rollers, or grain shoots out of pipes then satic can build up. this could easily lead to a spark causing an explosion in dusty or fumey places 

earthed or insulated 

• dangerous spark can be prevented by connecting a charged object to the ground using a conductor - earthing
• it provide an easy route for the static charge
• no charge can build up to give a shock or spark

paint sprays 

• spray gun is charged.
• each paint drop repels , theyre the same charge, you get a fine spray 
• obeject painted is given an opposite charge . this attract the fine spray 
• give even coat, hardly any paint wasted.

dust precipitators:

• smoke particles meet a wire grid or rods with a high voltage and negative charge 
• dust particles gain electrons and become negatively charged 
• negatively charged dust particles repel electrons on the plate, plates become positively charged 
• particle fall off the plate 

defibrillators:

• two paddles are placed on the patient chest to get good electrical contact 
• everyone move away so only the patient gets a shock
• charge passes through the paddles to the patient to make the heart contract 

• current = flow of electrical charge around a circuit. flow of electrons, amps A. 
• voltage = driving force that pushes the current round. measured in volts, V 
• resistance = is anything in the circuit which slows the flow down, measure in ohms 

• if you increase the voltage - more current will flow
• if you increase the resistance - less current will flow 

breaking a circuit 

• current flows only if theres a complete loop for it to flow 
• break the flow - current stops
• wires fuses and circuit breakers are safety features that break a circuit if theres a fault 

• live wire = carries the voltage. (brown)
• neutral wire = completes the circuit (blue). 
• earth wire and fuse = for safety and work together (yeallow and green)
• applicance with a metal case must be earthed to reduce electrical shocks. earthed condictor can never become live. 
• double insulated = appliance has a casing that non conductive .doesnt need an earth wire as it can become live

earthing and fuses 

• the surge in currents blows the fuse and causes the wire inside to melt
• cuts off the live wire because it breaks the circuit 
• make it impossible to get an electrical shock 
• stops the flex overheating, causes a fire and prevent further damage

variable resistors 

• a resistor is a component that reduces the current flowing in a circuit 
• a resistor whoses resistance be changed by twiddling a knob or something 
• resistance up, current drops
• resistance down, current goes up
• long wire have more resistance, less current flowing - longer wire, the more material electrical charge has to flow which increase the resistance.

calculating resistance 

resistance = voltage                                                                                                                                 current 

variable resistors 

• a resistor is a component that reduces the current flowing in a circuit 
• a resistor whoses resistance be changed by twiddling a knob or something 
• resistance up, current drops
• resistance down, current goes up
• long wire have more resistance, less current flowing - longer wire, the more material electrical charge has to flow which increase the resistance.

calculating resistance 

resistance = voltage                                                                                                                                 current 

• compressions = under high pressure (lots of particles)
• rarefractions = under low pressure (fewer particles)
• wavelength = full cycle of a wave - crest to crest/ compression to compression 
• frequency = how many complete waves there are per second 
• high frequency = high pitch 
• amplitude = how much energy the wave is carrying or loud the sound 

• longitudinal waves = vibrations are along the same direction as the wave is travelling
• transverse = vibrations are at 90oc to the direction of travel of the wave 

kidney stones

• ultrasound waves cause kidneys stones to vibrate more. they then shatter and are small enough to pass through in the urine.

body scans

• ultrasound is sent through the body
• these waves reflect and refract due to different tissue density 
• these waves are reflected back at different times due to different densities 
• this information is processed by a computer to form an image 

x-rays 

• x-rays pass easily through soft tissues  - image of hard things 
• ultrasound is safe - doesnt damage living cells. x-rays are ionising radiation. they can damage living cells and cause cancer. 

• half-life is the time taken to for half of the radioactive nuclei now present to decay 
• short half-life means the activity falls quickly because lots of the nucleu decay in a short time
• long half-life means the activity fall more slowly because most of the nuclei dont decay for a long time

• nuclear radiation = alpha, beta and gamma = ionising radiation
• some materials absorb ionising radiation - enter living cells and intersct with molecules 
• ionisation occur particle gain or lose electrons 

• lower doses of ionising radiation cause minor damage without killing cells. this can give mutant cells which divide uncontrollably - cancer
• higher doses kill cells completely causing radioactive sickness 
• beta and gamma outside the body are the most dangerous
• alpha inside the body is the most dangerous 

x-rays and gamma rays are elecromagnetic waves

radiotherapy 

• high doses of gamma ray kill living cells - used to treat cancer
• gamma rays is rotated around the patient head to hit all areas of the tumour, limiting exposure to healthy cells
• limit exposure to healthy tissures or prevent exposure ions to healthy tissues
• possibility of shrinking tumour, getting rid of cancer, non invasive, quick recovery period 
• radiation sickness and doesnt garintee of removing the cancer 

tracers in industry 

• the splitting of uranium atoms
• Uranium or plutonium isotopes are normally used as the fuel in nuclear reactors, because their atoms have relatively large nuclei that are easy to split, especially when hit by neutrons.
• When a uranium-235 or plutonium-239 nucleus is hit by a neutron, the following happens:

• the nucleus splits into two smaller nuclei, which are radioactive
• two or three more neutrons are released
• some energy is released

• is the opposite of nuclear fission
• two light nuclei combine to create a a larger nucleus 
• example, two atoms of different hydrogen isotopes combing to form helium 
• fusion realease a lot of energy 
• fusion doesnt leave behind much radioactive waste  
• problem - only happen at high pressure and temperature 
• hard to build