p2 topic 1 notes

8/21/2019 P2 Topic 1 Notes

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Topic 2 – Controlling and using electric currents

CURRENT AND VOLTAGE

Series circuits (first diagram) consist of just one continuous loop – they have no junctions

Parallel circuits (second diagram) have different branches, which form separateloops

Measuring current:

The size of a current (in amps) is measured using an ammeter

mmeters are always placed in !series" with other components in a circuit

The electrons aren"t used up and the current leaving the cell is the same as thecurrent that flows bac# into the cell$

o an ammeter can be placed anywhere in a series circuit$it will alwaysgive the same reading (e%g in series circuit below, it"s &%' everywhere)

Measuring oltage:

Potential difference (i%e the voltage) is measured using a voltmeter

oltmeters measure the difference in energy between the electrons going into thecomponent and those coming out – they"re always placed in parallel with the

component (i%e on a separate branch)o *%g in the diagram below, the voltmeter is measuring the potential

difference (i%e the difference in energy between electrons going in andthose coming out) across the light bulb

o The higher the potential difference, the more energy emitted from thecellthe bigger the current$the brighter the bulb

The potential difference is the energy transferred (to a component) for each unit of charge that passes through that component

o *nergy is measured in joules, charge is measured in coulombso + volt + joule per coulomb

-n a parallel circuit, when current reaches a junction, the current splits into two$o *%g in diagram above, when the &%' current reaches the junction, it splits

into &%. and &%/ o 0ote current is conserved 1 i%e none is lost


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C!ANG"NG RE#"#TANCE#

Resistance

2esistance is a way of measuring how hard it is for electricity to flow – it"smeasured in ohms (3)

The higher the total resistance in a circuit, the smaller the current

the current flowing in a circuit can be changed by changing the resistance – thiscan be done by using a variable resistor (or by putting a different resistor into thecircuit)

The size of the current flowing in an electric circuit depends ono the potential difference of the cell4power supplyo the resistance of the circuit

relationship between resistance, current and voltageo Potential difference (volts, ) current (amps, ) 5 resistance (ohms, 3)o - 5 2 o -%e the bigger the voltage and the smaller the resistance, the bigger the

current

*%g what potential difference is needed to ma#e a . current flow through a +& 3resistor6

o Potential difference +& 5 . .&

#o$e electrical co$ponents c%ange t%eir resistance depending on t%e

potential di&&erence'

+% 7ilament lampso s the potential difference increases, the filament lamp gets hotter and its

resistance increaseso current vs voltage graph flattens off at high voltages

.% 8iodeso 9onduct electricity in one direction onlyo if a potential difference is applied in the other direction, no current will

flow

0ote$o The resistance of fi5ed resistors isn"t affected by the potential differenceo in the presence of a fi5ed resistor there"s a directly proportional

relationship (i%e straight line graph) between current and voltage

#o$e electrical co$ponents c%ange t%eir resistance depending on t%e

conditions surrounding t%e$'

:ight1dependent resistor (:82)


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o -ts resistance is large in the dar# and decreases when light is shone on it$i%e the greater the light intensity, the smaller its resistance

Thermistors as the temperature increases, their resistance increases

TRAN#(ERR"NG ENERG)

;hen current flows through a resistor, energy is transferred to the resistor and it becomes warm

This happens with all components$e%go in a motor, the main energy transfer is from electrical energy to #inetic

(movement) energyo


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VECTOR# AND VELOC"T)

8isplacemento -n a .&&m race, all runners cover a .&&m distanceo uantities

Distance-ti$e grap%s:

graph in which distance is plotted against time is called a distance1time graph

Time and distance are used to calculate speedfrom a distance1time graph, wecan tell how fast an object is moving

o


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Point 8 E'minutes, @#m

speed gradient change distance 4 change in time

speed gradient . 4 +& &%. #m4min +. #m4hour

ACCELERAT"ON

Foving things speed up or slow down all the time – this change in velocity iscalled acceleration

cceleration has both a size and directionis a vector >uantityo Positive acceleration means the object is speeding upo 0egative acceleration means the object is slowing down

cceleration can be calculated from the e>uationo acceleration (m4s.) change in velocity (m4s) 4 time ta#en (s)o change in velocity final velocity (v) 1 initial velocity (u)o a (v – u) 4 t

*%g racing car starts from & m4s and reaches a velocity of '& m4s in ' seconds%;hat is its acceleration6

o cceleration ('& – &) 4 ' +& m4s.

o +& m4s. means that each second the velocity of the car increases by +& m4s(i%e +& metres per second, per second units of acceleration are m4s.)

*%g. during landing, a space shuttle slows down from G& m4s to .& m4s in .&s%9alculate its acceleration

o cceleration (.& – G&) 4 .& 1'&4.& 1.%' m4s.

o The minus sign shows that the space shuttle is slowing down (i%e negativeacceleration)

VELOC"T)-T"ME GRA.!#

velocity1time graph shows how the velocity of an object changes with timeo horizontal line means the object is travelling at a constant velocity

The higher the line, the higher the velocityo straight sloping line shows the object is accelerating

The steeper the line, the greater the acceleration -f line slopes upwards, object is speeding up (positive acceleration)

-f line slopes downwards, object is slowing down (negativeacceleration)

*%go t point 1 car is stationary


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o Cetween points and C, 9 and 8, * and 7, and, H and < – car isaccelerating

Cetween points and C, 9 and 8 and H and < – positiveacceleration (car is speeding up)

Cetween points * and 7 – negative acceleration (car is slowing

down)o Cetween C and 9, 8 and *, and 7 and H – car is travelling at a constant

velocityo The car is travelling at the highest velocity between points 8 and *

Calculating acceleration &ro$ a elocit+-ti$e grap%:

The acceleration of an object between two points can be calculated from avelocity1time graph, using the e>uation on the previous page

*%g acceleration between points 9 and 8 (on diagram above)o final velocity E& m4s$$initial velocity .& m4s$$time + secondo acceleration .& 4 + .& m4s.

Calculating distance &ro$ a elocit+-ti$e grap%:

The area under a velocity1time graph tells us the distance the object has travelled• To calculate the area under a velocity1time graph$

o you split the area under the graph into shapes (s>uares and triangles),calculate each bit separately, and then add everything together

• *%g (for diagram directly above)o rea of triangle I base 5 height$ area + 5 E Emo rea of s>uare base 5 height$area . 5 E @mo distance travelled @m J Em +.m

• (ORCE#

• 7orces can ma#e objects change speed, shape or direction•

force is a vector >uantity because it has both a size and direction• 7orces are measured in newtons (0)• There are lots of different types of forces

o Kpthrust4lift – these act upwards (in air)o ;eight (gravity) – this acts downwardso friction4air resistance4drag – these act against the direction of movement

(friction – on land, air resistance – in air, drag – in water)o Thrust4driving force – these act in the direction of movement$they are

forces produced by engines that push vehicles forwards (thrust – in air,driving force – on land)

o

Push4pull – these are forces that also act in the direction of movement, butare generated by direct contact between objects (not by engine power)


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• Action and reaction &orces:

• ;henever two objects touch, they interact with each other%%%o the forces they e5ert on each other are e>ual in size and opposite in

directiono These forces are #nown as !action" and !reaction" forceso s a pair they"re called an !action1reaction" pair

• *%g a boo# resting on a tableo The weight of the boo# e5erts a downward force on the table – this is the

!action force"o The table e5erts an e>ual and opposite (i%e upward) pushing force on the

boo# 1 this is the !reaction force"o ;ithout this reaction force, the boo# would fall through the table

• ction and reaction forces are used to propel roc#etso Hases are pushed out from the rear of the roc#et – this is the action forceo The reaction force from the gases pushes the roc#et forwards

• (ree-/od+ &orce diagra$s:

• free1body diagram shows the different forces acting on an object

• The arrows show the direction in which the forces act• The length of the arrows shows the size of the forces (the longer the arrow, the

bigger the size of the force)• RE#ULTANT (ORCE#

• Resultant &orce:

• ;hen more than one force acts on an object, the effect is the same as if they werecombined into a single force – the !resultant force"

• To wor# out the resultant force, you add together all the forces acting in onedirection, and then subtract them from all the forces acting in the oppositedirection

• *%g for the diagram aboveo Total thrust force to the left +&&,&&& 0o Total air resistance force to the right .',&&& 0o resultant force +&&,&&& – .',&&& G',&&& 0 of force to the left

• 0alanced &orces:

• 7orces that are e>ual but act in opposite directions are !balanced"• ;hen all forces are balanced, the resultant force on an object is zero

o the object"s movement, shape or direction will not changeo So if object was stationary, it will remain stationary$if it was moving, it

will continue to move at the same velocity (i%e it will continue to move at

the same speed and in the same direction)• Un/alanced &orces:


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• -f forces acting in opposite directions are not e>ual, the forces are !unbalanced"• ;hen forces are unbalanced, the resultant force on an object is not zerothe

object will accelerate in the direction of the resultant force• -n the diagram above$

o The thrust is the force produced by the plane"s engines, moving the planeforwards

o s the plane flies, air molecules push against the plane, producing anopposite force called air resistance

o The thrust is greater than the air resistance (as thrust arrow is longer) forces are unbalancedthere"s a resultant force in the direction

of the thrust force plane accelerates in the direction of the thrust force (left)

(i%e plane"s velocity increases)• -f thrust and air resistance forces were balanced, then the resultant force would be

zero and the plane would continue to fly at the same velocity• -f air resistance was greater than the thrust force$

o there would be a resultant force in the direction of air resistanceo there would be a (negative) acceleration in the direction of the air

resistance (right) (i%e the plane"s velocity would decrease)• 0ote remember when answering >uestions on forces that there are no air particles

in space (space is a vacuum)there is no air resistance in space• (ORCE# AND ACCELERAT"ON

• The rate at which an object accelerates depends on$o the size of the (resultant) force – the greater the resultant force, the greater

the acceleration of the objecto the mass of the object – the greater the mass of the object, the smaller its

acceleration• e>uation lin#ing acceleration, force and mass

o 7orce (0) mass (#g) 5 acceleration (m4s.)o 7 m 5 ao + newton is the force needed to accelerate a mass of +#g by +m4s.

• *%g a car"s acceleration is / m4s.% -t weighs +'&g% ;hat is the force provided bythe engine6

o 7orce +'&& 5 / E,'&& 0• TERM"NAL VELOC"T)

• Mass and *eig%t:

• Fass (measured in #g) is the >uantity of matter there is in an object and does notchange

• ;eight (measured in 0) is a measure of the pull of gravity on an object$ifgravity changes, weight also changes

• The strength of gravity is called the !gravitational field strength" (measured in 04#g)

• Ln earth, the gravitational field strength is +&04#geach #ilogram is pulled downwith a force of +&0

• The weight of any object on earth can be calculated using the e>uationo weight (0) mass (#g) 5 gravitational field strength (04#g)o ; m 5 g


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• *%g what is the weight of a G'#g person on *arth6o weight G' 5 +& G'& 0

• *%g. what is the weight of a G'#g person on the moon6 The moon"s gravitationalfield strength is about +%'04#g$

o ;eight G' 5 +%' ++.%' 0o 0otice how person"s mass (G'#g) is the same on the moon as it is on *arth

1 mass never changes (it"s not affected by gravitational field strength)o Person"s weight instead is much lower on the moon (++.%' 0) than on

*arth (G'& 0) because the gravitational field strength is much smaller onthe moon than on the *arth

• Acceleration o& &alling o/1ects:

• :arger masses need more force to get them to accelerate than smaller masses(recall the e>uation force mass 5 acceleration)

• Cut as the mass increases, so does the force from gravity (weight)(recall the e>uation weight mass 5 gravitational field strength)

• Ln *arth, there are air particles, which generate air resistanceo if a hammer and a feather are dropped, the hammer hits the ground first

because it is slowed down less by air resistance• uic#ly towards the ground

• s the s#ydiver gains velocity, the size of the air resistance force increases$o the resultant force downwards is smaller o s#ydiver is still accelerating down towards the ground, but the size of

the acceleration is smaller • *ventually the weight and air resistance become balanced$

o resultant force is now zeroo s#ydiver stops accelerating$i%e the s#ydiver continues to fall towards

the ground, but now at a constant velocity• This constant (ma5imum) velocity reached when the air resistance force balances

the weight is called the !terminal velocity"Topic 4 – Mo$entu$5 energ+5 *or and po*er

#TO.."NG D"#TANCE#

#topping sa&el+:

;hen a driver sees a problem ahead, the car travels some distance before thedriver reacts and steps on the bra#es – this is called the !thin#ing distance"

Lnce the driver has stepped on the bra#es, the car will travel some distance beforeit comes to a complete stop – this is called the !bra#ing distance"


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The overall !stopping distance" for a car thin#ing distance J bra#ing distance

(actors a&&ecting stopping distances:

0ote ma#e sure you realise that some factors affect just the thin#ing distance,some just the bra#ing distance, and some affect both

+% Person"s reaction time (i%e time it ta#es to respond to danger)o The slower a person"s reaction time, the longer the thin#ing distanceo Tiredness, illness, or ta#ing drugs or alcohol can all slow down reaction

times

.% Speed of the vehicleo The faster the vehicle is travelling, the longer both the thin#ing distance

and the bra#ing distance

/% State of the car"s bra#es and road conditionso 7or a car to come to a stop there must be friction created between the car"s

tyres and the road$

the more friction between the tyres and the road, the smaller the bra#ing distance

o The amount of friction between the tyres and the road depends on

the condition of the car"s bra#es (the better the bra#es, the morefriction they createshorter bra#ing distance)

condition of the road surface (e%g if the road is wet or has loosegravel, less friction is createdlonger bra#ing distance)

o 0ote due to longer bra#ing distances in wet conditions, drivers shouldleave more of a gap between their car and the car in front when it is raining

E% Fass of the vehicleo -f a vehicle has more mass, more force is needed to ma#e it slow downo the heavier the vehicle, the longer the bra#ing distance

MOMENTUM

Fomentum is a measure of how strongly something is moving$o momentum (#g m4s) mass (#g) 5 velocity (m4s)o -%e the heavier the vehicle and the faster it is travelling, the greater its

momentum

*%g what is the momentum of a monster truc# (mass E'&g) when travelling at+.m4s, in an eastward direction6

o Fomentum E'&&& 5 +. 'E,&&& #g m4s east

Fomentum has a size and direction so is a vector >uantityo when giving an answer, you should state not only the amount of

momentum an object has (the !size") but also the direction of thatmomentum (which will be in the same direction as the velocity)

Conseration o& $o$entu$:

;hen a moving object collides with another objecto their masses are added together their combined speed will be slower o


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• Cefore collisiono Lbject on the left has a momentum +' 5 E D& #g m4s to the righto Lbject on the right has a momentum & 5 . & #g m4s

• fter collisiono 9ombined objects have a momentum +& 5 D D& #g m4s to the right

• the combined momentum of the objects before and after the collision is thesame

• This demonstrates that when objects collide, momentum is conserved (i%e it is

transferred to the other object without any being lost)• MOMENTUM AND #A(ET)

• ;hen travelling in a car, passengers are going at the same speed as the car • -f a car bra#es suddenly, there"s a rapid change in momentum, and a strong force

is applied to the passengers 1 this can result in serious injury (e%g passengers cansmash their heads against the windscreen)

• The !rate of change of momentum" (i%e the speed at which the momentum of anobject changes) is e>ual to the force applied to the object$

o The rate of change of momentum change in momentum 4 time ta#en forthat change

o force (0) change in momentum (#g m4s) 4 time ta#en for that change(s)

o *%g what is the force needed to change a cyclist"s momentum by .E #g m4sin E seconds6

7orce .E 4 E D 0• So in a car crash$

o the >uic#er the rate of change of momentum (i%e the >uic#er the passenger"s momentum decreases to &), the more force applied to the passengersthe more li#ely the passengers are to get hurt

o safety measures in cars try to reduce the rate of change of momentum of

passengers (i%e they try to increase the time it ta#es for the passenger"smomentum to decrease to &) so that force applied to the passengers issmaller

• 0ote the !rate of change of momentum" is basically the same as saying the !rateof change of velocity" because the time it ta#es for velocity to decrease to & is thesame time it ta#es for momentum to decrease to & (momentum velocity 5 mass)

o -ndeed, e>uation above can be re1written as$ force M(final velocity 5 mass) – (initial velocity 5 mass)N 4 time 7 (mv – mu) 4 t

• Ve%icle sa&et+ $easures:

•

+% Seat belts


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o -n an accident, seat belts stretch passenger"s velocity is slowed downmore gradually

o it ta#es longer for passenger"s momentum to be slowed to zero (i%e therate of change of momentum is reduced)

o force applied to the passengers is lesso reduced chance of injury

• uashes and folds in a

specific wayo This crumpling and folding reduces the momentum of the car over a longer

period of time (i%e reduces the rate of change of momentum)o the impact forces on the passengers are lesso reduced chance of serious injury

• 6OR7 AND .O6ER

• !;or#" is done when energy is transferred from one form to another o *%g car bra#es !do wor#" by transferring #inetic energy to thermal energy

• The amount of !wor#" done is e>ual to the amount of energy transferred• *nergy is measured in joules (?)wor# is also measured in joules• Calculating *or done:

• wor# done (joules, ?) force (newtons, 0) 5 distance moved in the direction ofthe force (metres, m)

o * 7 5 d• *%g a sailor lifts a /&& 0 sail from the dec# to a height E m up%


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o Hravitational potential energy (?) mass (#g) 5 gravitational field strength(04#g) 5 vertical height from ground (m)

o HP* m 5 g 5 h• *%g on earth the strength of the gravitational field is +&04#g% ;hat is the

gravitational potential energy gained by a '&g Fars 2over when it"s lifted +'m

by a test crane on *arth6o HP* '&& 5 +& 5 +' G',&&& ?

• 7inetic energ+:

• Ainetic energy is another name for movement energy• The #inetic energy can be calculated using the e>uation$

o #inetic energy (?) I 5 mass (#g) 5 (velocity). (m4s.)o A* I 5 m 5 v.

• *%g what is the #inetic energy of a D'#g girl running at Dm4s6o A* I 5 D' 5 (D.) +,+G& ?

• Conseration o& energ+:

• ;hen energy is transferred from one form to another, energy is conserved (i%etotal amount always remains the same$none is lost)

• *%go s an object falls, its gravitational potential energy is converted into

#inetic energyo ;hen an object with gravitational potential energy falls down, the amount

of #inetic energy it has just before it hits the ground is e>ual to its initialgravitational potential energy (as all the HP* has been converted to A*)

• *%g when a '&g item was dropped, G'&&& ? of gravitational potential energywere all transferred to #inetic energy by the time it hit the ground%


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o -n an atom, the number of electrons number of protonsatoms have nooverall charge

• tomic number – number of protons in the nucleus of an atom$o ll atoms of a particular element have the same number of protonssame

atomic number o toms of different elements have different numbers of protons (no two

elements have the same atomic number)• Fass number – total number of protons and neutrons in the nucleus of an atom$

o The number of neutrons in an atom can vary• -n a chemical symbol, e%g , the atomic number is the bottom number (the

smaller one) and the mass number is the top number (the bigger one)• "sotopes:

• -sotopes are different atoms of an element with the same number of protons, butdifferent numbers of neutrons (i%e same atomic number, different mass number)

• *%g atoms of lithium can e5ist as lithium1D and lithium1Go The number attached is the mass number of the isotope$

The nucleus of an atom of lithium1D has / protons and / neutronsits mass number D

The nucleus of an atom of lithium1G has / protons and E neutronsits mass number G

• "ON"#"NG RAD"AT"ON

• 2adioactive substances have unstable nuclei that emit ionising radiation (this is arandom process

• s they emit ionising radiation, unstable nuclei lose (release) energy and decay to become more stable

• -onising radiation is radiation that has enough energy to cause atoms to loseelectrons and become (positively charged) ions

• There are three main types of ionising radiation 1 alpha particles, beta particlesand gamma rays

• .roperties o& ionising radiations:

• lpha particleso contain two protons and two neutrons (same as the nucleus of a helium

atom)o have no electronso they have a charge of J.

• Ceta particles are electronsare negatively charged• Hamma rays

o are high1fre>uency electromagnetic wavestravel at the speed of lighto they have no charge

• A/ilit+ o& ionising radiations to ionise ato$s and penetrate $aterials:

• lpha particleso ery ionising (i%e they easily ma#e atoms lose electrons and become ions)o *ach time ionising particles ionise an atom, they lose some energyo alpha particles lose energy >uic#ly so don"t travel far into matter 1 i%e

they have a !short penetration distance" So alpha particles can be stopped by a few centimetres of air or a

few millimetres of paper


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• Ceta particleso Foderately ionising (less than alpha particles, more than gamma rays)o lose energy less >uic#ly than alpha particlesthey can penetrate further

into matter than alpha particles can Ceta particles can be stopped by a few millimetres of aluminium

• Hamma rayso ;ea#ly ionising (much less than both alpha and beta particles)o lose energy very slowlycan penetrate further into matter than both

alpha and beta particles can Hamma rays need thic# lead to stop them

• NUCLEAR REACT"ON#

• Radioactie deca+:

• The process of radioactive decay releases energy$o when alpha and beta particles are emitted from unstable nuclei at high

speeds, #inetic energy is releasedo when gamma rays are emitted from unstable nuclei at the speed of light,

the energy released is in the form of electromagnetic radiation• Lther nuclear reactions also release energy$• Nuclear &ission:

• Some large unstable nuclei can split into two smaller nuclei called daughter nuclei – this process is called nuclear fission

o *%g when a uranium1./' absorbs a neutron it becomes unstable andimmediately splits it into two smaller daughter nuclei, and two or moreneutrons are released

• 0uclear fission releases a huge amount of energy$

o Fost is in the form of #inetic energy because both daughter nuclei andneutrons are moving at high speedso Some thermal energy is also released

• Nuclear &ission - uncontrolled c%ain reactions:

• ;hen a uranium1./' nucleus splits, the neutrons released can be absorbed byother uranium1./' nuclei$

o These other uranium1./' nuclei will split into two smaller daughter nucleiand release more neutrons

o These neutrons can then be absorbed by yet more uranium1./' nuclei $and so on$

o This is called an !uncontrolled chain reaction"$


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-n uncontrolled chain reactions, lots of energy is released (throughnuclear fission) in a very short time – this occurs in an atomic

bomb• Nuclear &ission - controlled c%ain reactions:

• -f some of the neutrons released during nuclear fission are absorbed by other

materials, then chain reactions can be controlled$• *%g

o when a uranium1./' nucleus splits, all neutrons e5cept for one areabsorbed by other materials

o only one neutron from each fission event can be absorbed by anotheruranium1./' nucleus

o The chain reaction is now !controlled" because the chain reaction continuesat a constant ratethe amount of energy produced through nuclear fissionis regulated

• 9ontrolled chain reactions occur in nuclear reactors (see below)

• NUCLEAR ("##"ON "N NUCLEAR REACTOR#• 0uclear reactors in nuclear power stations convert (nuclear) energy contained in

the nuclei of uranium and plutonium ions into thermal energy using nuclearfission

• The rate at which nuclear energy is transferred to thermal energy is #ept constant by controlling the fission chain reaction$

o This is done by ensuring that only one of the neutrons released by thedecay of a uranium nucleus is absorbed by another uranium nucleus

o To achieve this, the e5tra neutrons that are released have to be absorbed –this is done by control rods in the reactor core$

Control rods:• 9ontrol rods contain elements that absorb neutrons$

o -f the rate of fission needs to be increased, the control rods are moved outof the corefewer neutrons are absorbed by control rodsmore neutronscan be absorbed by other uranium nuclei

o -f the rate of fission needs to be decreased, more control rods are movedinto the coremore neutrons are absorbed by control rodsfewerneutrons can be absorbed by other uranium nuclei

• ;hen the control rods are fully lowered into the reactor core, they absorb all theneutronsthe chain reaction stops and the reactor shuts down

• Moderators:

• 0eutrons emitted from the fission of a uranium1./' nucleus are moving very fast


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• To ma#e them more li#ely to be absorbed by other uranium1./' nuclei, they needto be slowed down – this is done by moderators in the reactor core

• Generating electricit+:

• +% Thermal energy from the core is transferred to the coolant (usually water at high pressure), which is pumped through the reactor

• .% This super1heated water is pumped to a !heat e5changer" where it"s used to produce steam

• /% The steam drives a turbine, which turns a generator • E% The generator transfers #inetic energy into electrical energy• Radioactie *aste:

• The products of nuclear fission (i%e the daughter nuclei and radioactive isotopes)are radioactive

• over time, radioactive waste builds up in the reactor core• NUCLEAR (U#"ON

•

0uclear fusion occurs when small nuclei combine to form larger nuclei• *%g when hydrogen nuclei fuse to form helium$

o There are two isotopes of hydrogen


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o The higher the temperature, the faster the nuclei movethe more li#elythey are to overcome their electrostatic repulsion and collide

• Knfortunately, the conditions that are re>uired for nuclear fusion (very hightemperature and pressure) are difficult to achieve and are very e5pensive

• it will be some time before fusion energy will become a viable energy source• ;Note; - Cold &usion:

• Scientists .& years ago claimed to have carried out nuclear fusion at '&9 – this became #nown as !cold fusion"

• The possibility of carrying out nuclear fusion at low temperatures was e5citing atthe time because it would be more convenient and less e5pensive

•


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o -:; includes metal cylinders that once contained the uranium fuel• 7or the ne5t tens of thousands of years after that – waste is called low level waste

(::;)$i%e waste is only slightly radioactivecan now be disposedo ::; includes clothing and cleaning materials from nuclear power stationso


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• The !half1life" is the time ta#en for the !activity" for a radioactive substance todecrease by half (i%e it"s the time ta#en for half of the nuclei in a sample of aradioactive isotope to decay and become more stable)

o The shorter the half1life, the >uic#er the isotope decays• The half1life of a radioactive sample is found by recording its activity over a

period of time 1 this is done using a Heiger1Fuller (HF) tubeo HF tube is connected to a counter – every time ionising radiation is

detected, it gives out a clic# o The !count rate" is the number of clic#s per secondo The time it ta#es for the count rate to halve is the half1life

• The half1life can be calculated from a graph$e%g (on ne5t page)

o ctivity of radioactive substance is initially @& counts per secondo -t ta#es D days for its activity to reduce to E&$its half1life is D days

• 0AC7GROUND RAD"AT"ON

• ;e are constantly e5posed to low levels of ionising radiation from space andfrom naturally radioactive substances in the environment 1 this is called!bac#ground radiation"

• ;hen scientists measure the activity of a source$o They first need to measure the bac#ground radiationo The bac#ground radiation is then subtracted from measurements to

give the corrected reading of the source"s activity• #ources o& /acground radiation:

• +% 2adon gas is the main source of bac#ground radiationo ;hen uranium in roc#s decays, it produces other radioactive isotopes

that also decay – one of these is radono 2adon diffuses into the air from roc#s and soil and can build up in

houses, especially if there is poor ventilationo The amount of radon in the air depends on the type of roc# and its

uranium content the radon content (and so also the bac#ground radiation)

varies according to where you are in the KA • .% Q1ray scans, gamma ray scans and radiotherapy treatment for cancer

contribute to bac#ground radiation


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• /% Some foods naturally contain small amounts of radioactive substances• Some bac#ground radiation comes from space$• E%


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• smo#e alarm consists of an electrical circuit with an air gap between twoelectrically charged (one positive, one negative) plates$

o The americium1.E+ source releases a constant stream of alpha particles, which ionise the air to give positive ions and electrons

o The electrons are attracted to the positively charged plate, positive ions

are attracted to the negatively charged platea small electrical currentflows in the air gap between the plates

o s long as the current flows, the alarm will not soundo ;hen smo#e gets into the air gap, the smo#e particles absorb the alpha

particlescurrent flowing across the gap decreaseso ;hen current drops below a certain level, the alarm sounds

• 0ote a source emitting alpha particles is used because alpha particles are veryionising

• C%ecing t%icnesses:

• Paper is made by s>ueezing wood pulp between rollers• The thic#ness of the paper is controlled by a detector, which counts the rate at

which beta particles pass through the paper$• ;hen the paper is too thin$

o :ots of beta particles penetrate the paper detector records a highcount rate

o computer senses the high count ratereduces the pressure applied tothe rollers paper is made thic#er

• ;hen the paper is too thic#$o 7ew beta particles penetrate the paper detector records a low count

rateo computer senses the low count rateincreases the pressure applied

to the rollers paper is made thinner • 0ote beta particles are used for this because they are moderately ionising

some pass through paper and others don"t, depending on the thic#ness of the paper

• Tracers in t%e eniron$ent:

• To detect lea#s in water pipes underground, a gamma source is added to thewater$a HF tube follows the path of the pipe, measuring the levels ofradiation

o ;here there"s a lea#, water flows into the surrounding earth

o The levels of radiation at this point are higher o These higher levels of radiation are detected by the HF tubeo the point where the water lea# has ta#en place can be located and

then fi5edTopic – #tatic and current electricit+

#TAT"C ELECTR"C"T)

Static electricity is caused by an electrical (!electrostatic") charge building up oninsulating materials – including on you

ll atoms contain electrically charged particles called protons and electronso

Protons have a positive charge and are found in the nucleus of atoms


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o *lectrons move around the outside of the atom at different distances fromthe nucleus – they are negatively charged

o The positive charges on the protons are balanced by the negative chargeson the electronsatoms have no overall charge

0ote the nucleus also contains neutrons, which have no charge

Generating static electricit+:

;hen two insulating materials are rubbed together, friction is generated andelectrons may be transferred from one material to the other (note protons can"t betransferred because they are fi5ed in the nuclei of atoms)

o The material gaining electrons now has more electrons than protonshasa negative charge

o The material losing electrons now has more protons than electronshas ane>ual positive charge

Lbjects charged with static electricity can attract or repel each othero -f the charges on the two objects are different, they will attract each other o -f the charges are the same as each other (i%e both positive or both

negative), the objects repel• -f you rub a balloon on a jumper you can get it to stic# to a wall – this process is

called charging !by induction" and the charge produced is an induced charge$• *5planation for this

o ;hen the balloon is rubbed against the jumper, electrons are transferredfrom the jumper to the balloonthe balloon becomes negatively charged

o ;hen the balloon is placed against the wall, the electrons in the wall arerepelled by the balloon"s negative charge and move away

o The positive charge left behind on the wall (the !induced charge") attracts

the negative charge on the balloon

the balloon stic#s to the wall• 6%+ it>s di&&icult to c%arge a conducting $aterial *it% static electricit+:

• -nsulating materials (e%g a polythene rod) do not conduct electricity$o electrons that are transferred cannot move through the material – i%e they

stay close together at the end of the polythene rodo static charge builds up at the end of the polythene rod

• 9onducting materials (e%g a metal rod) conduct electricity$o electrons that are transferred spread themselves out through the metal

rodo the e5tra static charge is difficult to detect

• This is why static electricity builds up between insulating materials and not between conducting materials

• U#E# AND DANGER# O( #TAT"C ELECTR"C"T)

• #%ocs &ro$ eer+da+ o/1ects:

• Rou can sometimes build up an electrostatic charge just by wal#ing on a carpeto s the shoes rub along the carpet, electrons are transferred from the carpet

to the person person becomes negatively chargedo -f the person then touches a conducting material (e%g metal object), the

person feels a small electric shoc# as electrons flow from the person,through the metal object to the earth

o The direction in which electrons flow depends on the charge of the object


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for a negatively charged object (as in this e5ample), electrons flowfrom the earth to the object

for a positively charged object, electrons flow from the earth to theobject

• The process of electrons flowing from a person to the ground through an object, or

the other way around, is called !earthing"• fter earthing, the person is discharged (i%e no longer has an electrostatic charge)

Lig%tning:

• :arge charges of static electricity can build up on clouds, causing electrons toflow through the atmosphere between the clouds and the ground (electrons canflow in either direction$i%e from ground to clouds or from clouds to ground)

• This produces the huge spar# that we see as lightning• Oerco$ing t%e dangers o& electrostatic c%arges:

• To reduce the dangers of the build1up of static electricity$o there needs to be a path between the object with electrostatic charge and

the ground, through which electrons can flow$ for electrons to flow along it, the !path" must be made of a material

that conducts electricity$in most cases, it"s made of metalo This earthing process discharges the object and prevents spar#s being

produced• *%g refuelling aircraft

o s fuel flows through a refuelling pipe, static electricity can build upo The aircraft can also build up a static charge as it flies through the air o a bonding line (a metal wire) is used to connect the aircraft to the earth

before it is refuelledo This discharges the aircraft of any electrostatic charge that may have built

upno spar#s are produced• similar problem can occur when tan#ers deliver fuel to filling stations

o -n this case, the hose used to fill the underground fuel tan#s is made of aconducting materialno spar#s are produced

• Uses o& static electricit+:

• Static electricity can be useful$• *%g it can be used in electrostatic spray painting to ma#e the spray spread out$

o The metal spray nozzle is connected to the positive terminal of anelectricity supplydroplets of paint pic# up a positive charge

o The positively charged droplets repel each other spread outo The object to be painted is given a negative chargeo the paint droplets are attracted to the surface of the object

• 0ote static electricity is also used in insecticide sprayers• ELECTR"C CURRENT#

• -n conducting materials (e%g metals), some of the electrons from each atom arefree to move about 1 this flow of electrons produces an electric current

• -n a piece of metal, the free electrons all move round in different directions• ;hen a metal wire is placed in an electrical circuit (it must be a complete circuit),

the cell (battery) pushes the free electrons in one direction around the circuit$o 9ells and batteries supply current that flows in only one direction – this is

called !direct current"


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• Henerators produce !alternating current" – i%e electrons change direction manytimes each second

• C%arge and current:

• n electric current is the rate of flow of charged particles• Knits

o 9harge – measured in coulombs (9)o 9urrent – measured in amperes (or amps, )

• The size of the elec tric current depends on how much charge is passing a point in a circuit each second

o + ampere is a flow of + coulomb of charge per second• The e>uation lin#ing charge and current

o charge (coulombs, 9) current (amps, ) 5 time (seconds, s)o B - 5 to -%e the more charge that passes a point in a circuit per second, the greater

the current• *%g

o a current of ' flows for +&s$how much charge has flowed through thecircuit6

o 9harge ' 5 +& '& 9

p2 topic 1 notes

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