Physics-P4

Question	Answer
what do most smoke alarms contain?	uranium 241 which emits alpha particles
what do most smoke alarms contain?	uranium 241 which emits alpha particles
the alpha particles cause..	air particles to ionise and the ions formed are attracted to oppositely charged electrodes in the alarm
this results in	a current flowing in the circuit and this means the alarm is working correctly
when smoke enters the space between the two electrodes	the alpha particles are absorbed by the smoke particles and so cannot ionise the air, this causes a shorter current than normal to flow sounding the alarm
A small amount of carbon in our atmosphere and in the bodies of animals and plants is radioactive ..	carbon 14
what do radioactive materials give out?	nuclear radiation
from..	the nucleus of their atoms
because...	they are unstable and therefore they decay naturally
how is radiation measured?	by the number of nuclear decays emitted per second
does the radioactivity of a radioactive substance decrease or increase with time?	decrease
what happens during alpha emission	an atom decays by getting rid of an alpha particle(of 2 electrons and 2 neutrons) and a new atom is formed
name 4 ways the nucleus of the new atom is different from the original atom	1.it is a different element 2.it has 2 fewer protons and 2 fewer neutrons 3.the atomic number has decreased by 2 4.the mass number has decreased by 4
Alpha particles are..	good ionisers because they are relatively massive so they hit atoms hard enough to strip electrons
REVISE CARBON DATING	REVISE DATING ROCKS
what is ionisation?	creating either a positively or negatively charged particle (ion)
what happens during beta emission?	an atom decays by changing a neutron into a proton. the high energy electron taken from the nucleus is a beta particle and a new atom is formed
the nucleus of the new atom is different from the original one because (4 reasons)	1.it is a different element 2.it has 1 more proton and 1 fewer neutron 3.the atomic number has increased by 1 4.the mass number remains the same
beta particles are	fast moving electrons and theyre not good ionisers because they are very light and cannot easily strip an electron from an atom
the nucleus of the new atom is different from the original one because (4 reasons)	1.it is a different element 2.it has 1 more proton and 1 fewer neutron 3.the atomic number has increased by 1 4.the mass number remains the same
what is a half life?	the time it takes for half the undecayed nuclei in a radioactive substance to decay
if the substance has a very long half life this means..	it stays active for a very long time
during alpha decay	2 2H
during beta decay	0 -1 B
what is a gamma ray?	an electromagnetic wave
what is background radiation?	radiation that occurs naturally in the environment and is around us all the time
where is it most released from?	radioactive substances in soil and rocks
how can the level of background radiation vary?	depending on the rocks in the area
what else contributes to background radiation?	cosmic rays
what other un natural way causes background radiation?	waste products from hospitals and industry
what are radioactive isotopes used for?	tracers in industry and hospitals to find out what is happening inside objects
3 ways they are used in industry?	1.track the dispersal of waste 2.find leaks and blockages in underground pipes 3.find the routes of underground pipes
A gamma source is used in tracers because..	gamma can penetrate through to the surface
the progress of material is tracked by a detector above the ground so	1. if theres a leak the radioactive material will escape and be detected at the surface 2.if there is a blockage the radioactive material will stop flowing so it cannot be detected after this point
what is ultrasound?	the name given to sound waves that have frequencies higher than 20,000 Hz, (above the human hearing range)
what type of wave does ultrasound travel in?	longitudinal wave
what is the amplitude?	the maximum disturbance caused by the wave
what is the wavelength?	the distance between two corresponding waves
what is the frequency of a wave?	the number of waves produced per second
Name two things ultrasound can be used for	1.ultrasound imaging-look inside people(scanning) 2.breaking down kidney stones
what is ultrasound imaging and body scans?	looking inside the body, measure the speed of blood flow, check babies development before birth, build up picture of organs in body, including heart, lung, liver, and detecting gallstones and tumours, no risk to mother or baby in prenatal scanning
how is ultrasound used when breaking down kidney stones?	they can be removed without the need for painful surgery. Ultrasonic waves cause the kidney stones to vibrate, making them break up, they are then passed out the body in urine
where are ultrasound waves partly reflected?	at a boundary as they pass from one substance into another
what are two main advantages ultrasound has over x-ray imaging?	1.it is able to produce images of soft tissue 2.it does not damage living cells
what do all waves do?	transfer energy from one point to another without transferring any particles
what happens to the particles in longitudinal waves?	each particle moves backwards and forwards about its normal position parallel to the direction of wave movement
what happens to the particles in transverse waves?	each particle moves up and down about its normal position at right angles to the direction of the wave movement
what is a circuit?	a complete loop that allows an electric current to flow through
electrons flow around the circuit from the...	negatively electrode to the positive electrode
what is resistance?	a measure of how hard it is to get a current through a component in a circuit at a particular voltage.
what is resistance measured in?	ohms
give three ways a current through a circuit can be controlled	1.a fixed resistor 2.a longer piece of resistance wire 3.a thinner piece of resistance wire 4.a variable resistor- a resistance that can be altered
for given resistor..	current increases as voltage increases and current decreases as voltage decreases
for fixed resistor...	current decreases as voltage increases and current increases as voltage decreases
THE LIVE WIRE IS	BROWN and carries the current to the appliance at about 230 v, fuses, circuit breakers and switches are all part of the live wire circuit
THE NEUTRAL WIRE	IS BLUE, completes the circuit and carries current away from the appliance, BOTTOM LEFT
THE EARTH WIRE	is green and yellow and is the safety wire that stops the appliance from becoming live, LEFT HAND SIDE
whats the difference between a fuse and a circuit breaker? and what are they both?	circuit breakers can be reset but fuses have to be replaced. They are both safety devices
what do they do?	they prevent fires, injury, death, overheating by breaking the circuit of the appliance if a fault occurs
4 steps to how a fuse works	1.the fuse wire gets hot and melts or breaks down 2.the circuit is broken so no current can flow 3.the fuse prevents the cable overheating 4.the appliance is protected
but what needs to be in place for this safety feature to work?	the current rating needs to be just above the normal current that flows through the appliance
all electrical appliances with outer metal cases must have an	EARTH WIRE to protect the appliance and the user
this means...	the outer case of the appliance is connected to the earth pin in the plug through the earth wire
how does this work?	1.a fault in the appliance causes it to become live 2.the circuit short circuits because the earth wire offers less resistance. the charge on the metal casing flows along the earth wire as a very large current 3.the fuse wire melts 4.the circuit is broken 5.the appliance and user are protected
all appliances with outer metal cases...	have to be earthed
the appliances with insulated outer cases need..	2 wires (the earth wire is missing).
why don't these appliances need to be earthed?	because they are double insulated, it does not matter if the live part touches the case because it is insulated
double insulated symbol	Image: Double-Insulated-Symbol (image/jpg)
what is an insulating material?	A material containing air pockets that reduces heat loss by conduction
how can a charge be built up between 2 objects?	2 insulating materials are rubbed together
what is this charge called?	static electricity
why does the electricity stay on the material and not move?	due to the transfer of electrons
what charge do electrons carry?	negative charge
what charges are the materials left with after static electricity has taken place and the electrons have transferred?	one is left with a positive charge and on is left with a negative charge
give 4 examples of when static electricity can occur	1.rubbing a balloon against a jumper 2.rubbing a duster against a haircomb 3.a duster brush attracting dust making it more effective 4.synthetic clothing sticking to the persons body
how can you discharge an object?	by earthing it
what happens during this process?	electrons are transferred from the charged object to earth
if you become electrically charged earthing can result in you getting an....	electrostatic shock
give an example of when earthing occurs?	if someone gets charged by friction between the soles of their feet and the carpet(insulator)when walking then touches a water pipe eg radiator the charge is earthed resulting in an electrostatic shock
name some dangers that can occur with static electricity	flour mills have atmospheres with extremely flammable gasses, a discharge of static electricity eg a spark can lead to an explosion so factories need to take precautions to insure no sparks are ignited
and another one..	when large quantities of charge could flow through your body to earth eg LIGHTNING
give two examples of when static electricity is a nuisance	1.can cause dust+dirt to be attracted to insulators, such as tv screens, computer monitors 2.it can cause some fabrics to cling to your skin
two insulating materials with the same charge will	REPEL EACH OTHER
two insulating materials of the opposite charge will	ATTRACT EACH OTHER
the material that receives electrons becomes..	negatively charged
due to..	excess electrons
the material giving up electrons becomes..	positively charged due to the loss of electrons
the atoms that become charged are then called..	ions
give 3 ways the chance of receiving an electric shock can be reduced..	1.ensuring appliances are correctly earthed 2.using insulation mats effectively 3.wearing shoes with insulating soles
lorries that contain flammable gasses, liquids, powders need to be earthed before unloading because..	friction can build up of charge which could lead to a spark which could then ignite flammable substances
connecting an aircraft to a fuel tanker...	makes sure that any charge built up on the fuel by friction (as it flows through the pipe) flows to earth making sure there is no discharge and spark to ignite the fuel
name 3 things static electricity can be used for	1.defibrillators (restarting the heart when it has stopped) 2.dust precipitators (reducing smoke particles in chimneys) 3.spraying (crop spraying+paint spraying a car)
how is a defibrillator used?	1.two paddles are charged and put in good electrical contact with the patients chest 2.the defibrillator charges into the patient 3.charge is then passed through the patient to make the heart contract
how are dust precipitators used when cleaning chimneys?	the metal plates in dust precipiators are at high voltage, there is also high voltage grids lower down the chimney that make the dust particles charged. the charged dust particles are attracted to earthed metal plates where they clump together then when heavy enough fall back down the chimney or when the plate is struck
how is static electricity used in spray painting a car?	1.the paint gun is negatively charged 2.paint particles become negatively charged so they repel and spread out evenly 3.the car panel that is being sprayed is positively charged 4. paint from negatively charged paint gun is attracted to positively charged panel
resulting in..	a fine line spray so it is applied evenly, resulting in a neutral painted car panel, also meaning less paint is wasted and even the back and sides of car that would be in the shadow of the spray receive a coat of paint

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