EDEXCEL A-LEVEL PHYSICS UNIT 4 EXTRA NOTES

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1 EDEXCEL A-LEVEL PHYSICS UNIT 4 EXTRA NOTES

2 Newton s Second Law of Motion in terms of momentum: (The) force (acting on a body) is proportional/equal to the rate of (1) change of momentum (1) and acts in the direction of the momentum change Alpha particle travels faster than any other new elements formed after radio active alpha decay because its mass is smaller/lighter So higher speed for the same (magnitude of) momentum. the 2 new particles formed travel in: Opposite directions/along a line experiment to find speed of 2 trolleys: 2 light gates (1) Gate gives time trolley takes to pass [ not just the time ] (1) Speed = length of interrupter /time taken (1) OR 2 ticker timers (1) Dots at known time intervals (1) Speed = length of tape section/time taken (1) 3 [ruler + clock could obtain third mark only, specifying a length/time] Law of conservation of linear momentum Provided no external [other/resultant/outside] force acts (1) The total momentum (of a system) does not change / total momentum (1) before(collision) = total momentum after (collision) 2 [Total seen at least once] [Ignore all references to elastic and inelastic] [Do not credit simple statement that momentum is conserved] If the car is driven across the bridge repeatedly, at gradually increasing speeds, it is found that, above a certain critical speed, the car loses contact with the road at A, and takes off. explain what happens Required centripetal force > mg (so cannot be provided Apparently weightless This means no force exerted on/by surroundings OR R = 0 OR only force acting is weight (1) 2 why an object moving in a circular needs a resultant force on it? Resultant force: Direction of travel changing (1), Velocity changing/accelerating (1), Force is towards centre of circle (1), The direction of speed OR velocity is changing (1), There is an acceleration/rate of change in momentum (1) When vehicles corner on a level road, the resultant force is provided by friction. For a given vehicle and road surface, the friction cannot exceed a certain maximum value. Use these facts, together with the expression for the resultant force, to explain why roads designed for high-speed travel have no sharp bends.:: Why no sharp bends: Relate sharpness of bend to r (1), Relate values of, r and F (1), [e.g. if r large, force being too large/if r small, must be small to prevent force being too large] can be large without explain how it is possible for the ball to move with constant speed and yet still be accelerating when moving in a circular path: Explanation There is a resultant (or net or unbalanced) force (1) Direction of motion is changing (1) Velocity is changing (1) Velocity change implies acceleration (1) Force produces acceleration by F = ma (or N2) (1) Force (or acceleration) is towards centre / there is a centripetal (1) force (or acceleration) / no force (or acceleration) parallel to motion No work done, so speed is constant (1)

3 Describe how the energy of the proton is increased in a cyclotron. Give one reason why the energy cannot be increased indefinitely.:: 1. Each time it crosses gap/between dees it accelerated / is attracted / is given E 1 2. Idea that p.d. between the dees reverses while the proton completes half a revolution / c.e.p As energy becomes large the mass/inertia of the proton increases 1 [not protons hit edge ] 4. so it cannot exceed the speed of light [i.e. ref to c ]/synchronous property breaks down/formula no longer gives constant f Explain how the electron produces the white track in a bubble chamber:: Link track to bubbles (1), Which reflects light / are illuminated (1), (produced as) the electron / it ionises liquid / particles / (1), H2 / air Explain the origin of the centripetal force that is making the electron spiral in this manner. Why does the radius of the circle in which it is moving gradually decrease::: Mention of B field/f = Bqυ/ F = Beυ/ FLHR (1) B is perpendicular to υ/ direction of motion / in or out (1) of page Electron loses energy/slows down (1) Colliding with / interacting with / ionising liquid particles / H2 (1) Describe how the protons are accelerated as they move along the linac and explain why the tubes get longer towards the right.:: Protons drift/move uniformly inside tubes (1) Accelerate between the tubes/in the gaps (1) Alternating p.d. reverses while p is in tube (1) The tubes must get longer as p speeds up (1) For time inside tube to be constant or to synchronise movement with the pd (1) The emerging protons in a linac can be made to collide with a target of fixed protons or a similar beam of protons travelling in the opposite direction. State some advantages of either or both experimental arrangement(s). Fixed target: Large(r) number of /more collisions or more likely to get collisions, [not easier to get collisions] (1) Other particle beams produced (1) Colliding beams: More energy available for new particles (1), p = 0 so all energy available (1) experiment to find structure of : 1. proton: deep inelastic scattering experiment 2. atom: Rutherford alpha particle scattering exp.

4 W particle:: 1. Exchange particle 2. Change in quark flavour / strangeness not conserved 3. Charge conservation requires negative particle n = udd and p = uud β and v have no quarks / are leptons / are fundamental p n +β+ and ν [on RHS, allow e+] [beta+ decay] Weak interaction: Change of quark flavour / type: [d u (in β ) AND u d (in β+) [accept vice versa ] ], (anti) neutrino only affected by weak interaction Antimatter storage: Annihilates (On contact) with matter / container / protons / H OR Not charged: not affected by magnetic fields what change takes place in the nucleus of an atom during a beta minus decay reaction:

5 hadron: particle composed of quarks Binding energy: Energy required to separate a nucleus into nucleons Weak force affect all particles / matter Strong force only affect quarks Electromagnetic force affects charged particles / charges Faraday's law of electromagnetic induction states that the magnitude of the induced electromotive force (e.m.f.) is directly proportional to the rate of change of magnetic flux linkage in the solenoid or the rate at which a conductor cuts through the magnetic flux. PHY5 june 2002 ques 2b (imp): When a person speaks through the microphone, the diaphragm and the coil vibrate at a certain frequency. When the coil moves into the magnet, the change in flux linkage results in an induced e.m.f and induced current flows in the coil. When the coil moves out of the magnet, the change in flux linkage leads to an induced e.m.f., where the induced current flows in the reversed direction. Hence, an alternating current at a frequency equivalent to the frequency of the longitudinal sound wave, is produced and sent to an amplifier. why is there a loss of stored energy when a capacitor is connected in a charged circuit? 1. There's loss of stored energy when the capacitors are connected due to gain in internal energy during electrical work 2. There's loss of stored energy when the capacitors are connected because of the heating in the wires resulting in the dissipation of thermal heat. 3. There's loss of stored energy when the capacitors are connected due to work done in charges 4. There's loss of stored energy when the capacitors are connected because energy is needed to overcome resistance in wires. if there are 2 capacitors in parallel, and you have to find total energy then use capacitance and charge [add charges of the 2 capacitors] E=0.5*[Q 2 /C] The operation of transformer is based on the principle of electromagnetic induction. The primary coil is connected to power supply with an sinusoidal alternating current a current where the magnitude and direction changes continuously at a certain frequency. The alternating current produces a flux or magnetic field lines which build a link between the primary coil and secondary coil. Soft iron core is used to increase the magnetic field strength. The magnetic flux produced varies in magnitude and direction. Such changing magnetic flux produces an induced e.m.f. across the secondary coil. The induced e.m.f. varies in magnitude and direction as well. Consequently, the secondary voltage is also a sinusoidal alternating voltage. A step up transformer is a type of transformer where secondary coil has more number of turns than the primary coil, therefore the rate of change of flux linkage is more and thus more e.m.f is induced across the secondary coil. When the compression pulse [sent in a slinky acting as a solenoid] pass through the Hall probe, the magnetic field B increases because the coil gets closer together. if the area of an electric conductor is decreased, its resistance increases. june 2003 PHY5 ques 4: The oscillations of blade A are rapidly damped. As the blade A, which has low resistance, oscillates between the permanent magnet, there's a cutting of magnetic field line resulting in induced e.m.f and flow of current. Lenz's Law shows that the direction of these current is such that they oppose the motion of the blade, where two magnetic field produce an opposing force, and so damp its swing. While swinging from one side and cutting through the magnetic flux induces a eddy current, swinging from the other side and cutting through the magnetic flux induces eddy current in another direction. Kinetic energy has been converted to thermal energy, contributing to heat dissipation. As a result, damping occur very rapidly. Slot cuts in the blade greatly reduce the flow of eddy current as the resistance is higher, therefore weaker magnetic field surrounding it is created. However it has lower magnitude to oppose the magnetic field between two permanent magnet. Therefore it is lightly damped. Equipotential surface: Surface containing all points at the same (gravitational) potential (energy) investigate variations of B with perpendicular dis. r from wire in a region arnd the centre of the wire: Investigation 1. Name or describe apparatus for measuring B, eg Hall probe/search coil (with pre-calibrated meter) 2. Probe positioned so the B field is perpendicular to the Hall slice/probe 3. Appropriate method for measuring r perpendicular to wire described or shown on diagram OR repeat readings for each r OR keep current constant 4. Vary distance r and measure B (and r) each time OR reference to graph plotting how a step down transformer works: 1. AC/changing current in the primary, 2. Produces a changing B field, 3. B field carried through core (to secondary), 4. Changing B field over secondary induces emf, 5. Rate of change of flux linkage is less through secondary OR emf induced across sec. is less because it has less turns than primary OR explanation in terms of the turns ratio formula

proportional to the product of their charges [plural] and inversely proportional to

OR Either equation for F*, with valid word replacements for Q1, Q2 and r or r2

6 jan 2004 Q3d:. Induced current I 1 0 Time I 2 The force between two charged particles is directly) proportional to the product of their charges [plural] and inversely proportional to the square of their separation [not just radius ]. OR Either equation for F*, with valid word replacements for Q1, Q2 and r or r2 symbols. One mark for numerator, one for denominator. describe how u wud show experimentally that the charged stored on a capacitor is propotional to the pd across the capacitor for a range of pds:

7 A second wire carrying a current of the same size is placed parallel and near to L. The magnetic field along a line joining the wires is investigated and it is found that at a certain distance from L, no magnetic field can be detected. Explain this observation.

Rutherford experiment:: Observations: Most alpha went straight through (1) Some deflected (1) (Very) few came straight back/large angle (1) Conclusions: Atom mainly (empty) space (1) Nucleus contains

8 Rutherford experiment:: Observations: Most alpha went straight through (1) Some deflected (1) (Very) few came straight back/large angle (1) Conclusions: Atom mainly (empty) space (1) Nucleus contains most of the mass (1) (Nucleus) very small/tiny (1) (Nucleus) charged /positive (1) equations of motion are for use on rectilinear motion what happens to a capacitor when the switch is closed? :: Charges (1) Movement of electrons from one plate to the other OR one plate becomes + the other OR until pd across C equals Vsupply ROLE Of electric and magnetic field in a cyclotron::: Electric fields: Electric field provides force on the charge/proton (1) gives energy to /work done / E = qv/ accelerate protons (1) Magnetic fields: Force on moving charge/proton (1) Produces circular path/centripetal force (1) labelled diagram showing Dees with E field indicated across gap OR B field through Dees (1) E field is reversed/alternates (1) electric field exerts a force on a charged particle whereas a magnetic field exerts a force on a moving charged particle why fragments shoot out in all directions when a nucleus breaks up:: momentum (1) Zero / negligible momentum before (1) To conserve momentum (fragments go in all directions) (1) State the meaning of the term Nφ in faradays law (Magnetic) Flux linkage Explain the significance of the minus sign How tiny bacteria move is of interest in nanotechnology. Mycobacteria move byejecting slime from nozzles in their bodies.explain the physics principles behind this form of propulsion::

9 There is some uncertainty in the time a molecule with a particular mass will take tocover this distance.suggest two reasons for this.::: [june 2010 ques 15d] DC voltage graph: (Trace) always positive/not negative/not below 0/ if it was AC the graph would be positive and negative, Indicating one/same direction A teacher suggests that certain electronic circuits require a constant voltage supply to operate correctly.(i) A student places a capacitor across the terminals of this DC power supply. Suggest how this produces a constant voltage.::: Capacitor stores charge/charges up, (If voltage is constant) capacitor doesn t discharge explain the process by which proton is given E in a particle accelerator:: Electric field Does work on proton/applies a force /repel/attract qv / Fd / Eq explain y the angle between the collision is not 90degree:: Mass of incoming proton larger (than rest mass) due to moving near speed of light/high speed/high energy/relativistic Alt answer : image not in plane of two protons after the event Explain what a charge of +2/3 on a quark means: Which one of the following might not apply in interactions between sub atomic particles?:: matter conservation When identifying the charge on a particle, you must identify if it is positive, negative or has no charge. only charged particles give tracks Sometimes additions to a diagram can be helpful commutator keeps the current direction the same on left and right sides of the coil by reversing the current direction If you realise that a question is about Lenz's law,remember to talk about flux not fields and also mention induced e.m.f.

fundamental particle: Cannot be split further/has no internal structure / not made up of other particles Make sure field lines are drawn with a ruler and are equispaced if appropriate.

[The word majority is not enough - it is the vast majority or better still 'most'.

10 fundamental particle: Cannot be split further/has no internal structure / not made up of other particles Make sure field lines are drawn with a ruler and are equispaced if appropriate. Limit yourself to 4 lines This type of question on Rutherford s scatteringexperiment is likely to appear regularly and the answercould be learnt by candidates. [The word majority is not enough - it is the vast majority or better still 'most'. Some reflected back is not good enough, it needs to be very few] [Many candidates did not specify that "very few" are deflected through large angles. A number of answers blurred the distinction between at least two from straight though, small angle deflection and large angle deflection.] why electrons are particularly useful for investigating nuclear structure?:: Wavelengths need to be smaller than nuclei Proton is not uniform / has space (1) Contains quarks purpose of magnetic field in a cyclotron: Force on (charged) particles at right angles to motion (1) Causes circular motion [not spiral / curved] OR force/acceleration is centripetal. [It is because the force is at right angles tom the motion that there is a centriptal force and this is an essential part of the explanation] why pd used in a cyclotron is alternating:: (Protons) accelerated / given energy, in the gaps / between D s/from one D to the other (1) Every half rotation/semicircle later (polarity of D s) needs a change explain how the freq. must change as the proton gains more and more evergy in a cyclotron: Relativistic effect / v approaching c/mass increases (1) so frequency decreases jan 2011 ques 18:: PART A) Measurement of appropriate quantity e.g.height /distance /time (1) Calculate speed or inferred by an equation (1) Speed on impact (1) Statement of how method shows momentum has been conserved (1) [must include correct mention of mass and velocity] [correct description of measuring velocity directly with a sensor scores first two marks] PART B) Collisions inelastic / KE is transferred in collisions (1) to internal energy (of balls) [allow heat] / to KE of middle balls/to sound (1) Eventually stops because all energy is transferred

Number 1 QWC i and iii Spelling of technical terms must be correct and the answer must be organised in a logical sequence

Number 1 QWC i and iii Spelling of technical terms must be correct and the answer must be organised in a logical sequence 1 QWC i and iii Spelling of technical terms must be correct and the answer must be organised in a logical sequence Observations: Most alpha went straight through Some deflected (Very) few came straight