WJEC Physics for AS: Study and Rev Guide

▪▪ Pointer and Grade Boost : offer extra examination advice based on experience of what candidates need to do to attain the highest grades. ▪▪ Extra questions : feature at the end of each topic providing you with further practice at answering questions with a range of difficulty. Exam Practice and Technique The second section of the book covers the key skills for examination success and offers you examples based on suggested model answers to possible examination questions. First, you will be guided into an understanding of how the examination system works, an explanation of Assessment Objectives and how to interpret the wording of examination questions and what they mean in terms of exam answers. A variety of structured and QER practice questions is provided taken from across the AS specification and model answers given. This is followed by a selection of examination and specimen questions with actual student responses. These offer a guide as to the standard that is required, and the commentary will explain why the responses gained the marks that they did. Most important of all, we advise you to take responsibility for your own learning and not rely on your teachers to give you notes or tell you how to gain the grades that you require. You should look for extra reading and additional notes to support your study in physics. It’s a good idea to check the awarding body website – www.wjec.co.uk – where you can find the full subject specification, specimen examination papers, mark schemes and in due course examiner reports on past years’ exams. Good luck with your revision! Extra questions 1. Calculate the total U and D numbersbeforeandafter the interaction p+p → p+n+ p + . 2. Fromwhatyouknowabout the strongande-m force,howdoyouknow thatneutrinos (andantineutrinos) can’texperienceeither. 3. A p + can (occasionally)decayvia: p + → e + + n e .Show that thisdecay satisfies the conservation rulesandexplainwhich interaction is responsible. 4. A p – candecaybya similarmode to that inquestion3.Write thedecay equation. 5. The r + mesondecaysvia the strong interaction toa p + andanother hadron.Write theequation for thisdecayandexplainwhy this is theonly possibility. 6. The followingoccurs in theproton–proton chainof reactions in theSun: Be+e – → 7 4 Li+Y 7 3 Write this reactionat thequark leveland identifyparticleY,explaining youranswer. 7. The last stageof thepp I branchof theproton–proton chain in theSun is He+ He → 3 2 H 3 2 He+2 4 2 1 1 wherewehaveused thenuclear symbol for theprotons. Whichof the interactions is responsible? 8. Solarneutrinos canbedetectedonEarthusingdry-cleaningfluid! In the process,occasionallya Cl 37 17 nucleus is converted into Ar 37 18 with theemission ofanotherparticle.Writeanequation for this reaction, identifying the emittedparticle. 9. The solarneutrinoflux (i.e. thenumberofneutrinosperm 2 per second) at theEarth isenormous: ~ 7 × 10 14 m -2 s -1 ,yet theneutrinodetectorof volume1000m 3 onlydetectsa fewneutrinosperyear.Suggesta reason for this. 10.Some (most)of the following ‘reactions’ cannothappenbecause they violateoneormoreof the conservation laws. Identify these.For the others, statewhich interaction controls it. p+p → n+p+ π + , (ii)e + +e – → n, (iii)p+p → n+ Δ – + π +, (iv) Δ – →π + +n, (i) p+p → n+p+ π + , (ii)e + +e – → n, (iii)p+p → n+ Δ – + π +, (iv) Δ – →π + +n, (i) (v)u+e – → d+v e , (vi)p+e + → n+ Δ – +v e , (vii) ρ – →π – + π 0 (v)u+e – → d+v e , (vi)p+e + → n+ Δ – +v e , (vii) ρ – →π – + π 0 75 1.7Particles andnuclear structure Q & A 1 Seren’sanswer (a) (i) The force exertedmultiplied by thedistance 3 travelled in thedirectionof the force. 3 (ii) [F] =N = kgm s - 2 [d] =m 3 \ [W] =J = [F] × [d] = kgm 2 s - 2 3 (b) (i) D gpe =mg D h =70 × 9.81 × (120 sin 20) 3 = 28183.82739J = 28.2 kJ (3 s.f.) 3 (ii) D KE = æ ö æ ö - ç ÷ ç ÷ è ø è ø 2 2 2 1 1 1 2 2 mv mv 3 = æ ö æ ö ´ - ´ ç ÷ ç ÷ è ø è ø 2 2 1 1 70 21 70 6 2 2 3 = 14175J = 14.2 kJ 3 (c) (i) Energy can neither be created nordestroyed, but converted intoother formsof energy. 3 (ii) The gravitational potential energy that has been lost betweenAandB has been converted intoother formsof energy, 3 including thermal, kineticand sound. (d) Fx = - 2 2 1 1 2 2 mv mu 3 120 F = ´ - ´ 2 2 1 1 70 21 70 6 2 2 7 120 F = 14175 3 F = 118N (3 s.f.) 7 Examiner commentary (a) (i) Serenhas correctly included theoften- forgotten statementaboutdirection. (ii) Thefirstmark is for correctly identifying the force anddistanceunitsand the second for themanipulation.Note: Serenhasused squarebrackets, [. . .], to indicate ‘theunit of’,which isquick. (b) (i) Serenhasgained1mark for correct substitution and 1mark for theanswer. In this case, converting tokJ and expressing to3 s.f.gainednoextra credit. (ii) Fully correct.Note that, if Serenhad slippedup in thefinal calculation, she wouldhave received2marksbecauseher workingwas clearand correct. (c) (i) Amarkwhichmost candidatesachieve. (ii) Serenhas identified that the initialGPE was converted into severalother forms [i.e. not just kinetic]buthasmissedout any discussionofmechanism,e.g.workdone against friction/drag. (d) Serenhasused theprinciple:Workdone= energy transferandused it to calculatea force from the changeofKE.Unfortunately, shehas calculate the resultant force on the skier,not the resistive force. Serengains13outof16marks. ASPhysics:Study andRevisionGuide 168 (a) (i) Definework. [2] (ii) Henceexpress theunit ofwork, J, in termsof the SIbaseunitskg,mand s. [2] (b) 120m A B 20° A skier ofmass70kgdescends a slopeas shown.The skierpassespoint A at a speed of 6m s - 1 and B at21m s - 1 .Calculate for thedescent from A to B : (i) Thegravitationalpotentialenergy lostby the skier. [2] (ii) Thekineticenergygainedby the skier. [3] (c) (i) State theprincipleof conservation of energy. [1] (ii) Discussyouranswer to (b) (i)and (ii) in termsof thisprinciple. [2] (d) Calculate themean resistive force experiencedby the skierbetween A and B. [4] 5 How to use this book: