2016 PRELIM 2 PAPER 2 MARK SCHEME

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1 06 River Valley Hig Scool Prelim Paper Mark Sceme 06 PRELIM PAPER MARK SCHEME (a) V 5.00 X 85. 9V 3 I.7 0 X V I X V I X X X X [A0] Anomalous data can be identified. Systematic errors can be identified and eliminated from measured values Random errors can be identified and teir effects reduced. [B] Any of te 3 points. (a) force on body A is equal in magnitude to force on body B (from A) forces are in opposite directions forces are of te same kind F A = F B and t A = t B Δp = F A t A = F B t B (c) (i) grap: momentum cange occurs at same times for bot speres final momentum of spere B is to te rigt and of magnitude 5 N s cange in momentum / time = 9 / = 00 N to te left [C] 3 (a) circular loop θ F C N W bead No marks if forces not labelled or forces missing. Considering forces on te bead, River Valley Hig Scool Pg of 9 Year 6 H Pysics 9646 Preliminary Examinations II 06

2 06 River Valley Hig Scool Prelim Paper Mark Sceme N cos mg N sin F r tan g c mv r 0. sin sin 0.75 cos (c) θ will decrease, if circle is rotating at a slower rate, centripetal force will decrease tus te orizontal component of te reaction force will be smaller and θ will be smaller. 4 (a) Consider forces in orizontal direction, F E = Tsinθ --- () Consider forces in vertical direction, mg = Tcosθ --- () [C] Combining () and (), tanθ = F E mg = q 4πε 0 d mg --- (3) Considering geometry, d = lsinθ --- (4) [C] Combining (3) and (4) and sinθ = tanθ, q 4πε 0 d mg = d l d q l 0mg 3 (sown) Using d q l 0mg 3, 9 ( 0 ) ( 08. ) 3 d m 0 (0.00) g River Valley Hig Scool Pg of 9 Year 6 H Pysics 9646 Preliminary Examinations II 06

3 06 River Valley Hig Scool Prelim Paper Mark Sceme (c) (i) 3 q l Using d, d will not cange as te product of q and mg q will not lead to a cange in te equation wile m and l are also kept constant. Using tanθ = q 4πε 0 d mg since d and m are kept constant., te canges in te carges will not affect θ and θ (c) Source: ttp:// Correct E-field lines spacing (closer field lines nearer to carge A) Correct direction of E-field lines wit neutral point nearer to carge B Important: Te diagram is sould be drawn witout any intersection of field lines and te field lines sould be perpendicular to te surface of te carge. Te top and bottom alf of te diagram sould also be proportional. 5 (a) (i) B electron Circular Pat downwards [A electron E River Valley Hig Scool Pg 3 of 9 Year 6 H Pysics 9646 Preliminary Examinations II 06

4 06 River Valley Hig Scool Prelim Paper Mark Sceme Parabolic pat upwards [A Magnetic force provides for centripetal force Bqv = m v / r B = m v / qr = (9.0-3 )(.80 8 ) / (.60-9 )(0.0) = T Wen undeviated Magnetic force = electric force Bqv = qe v = E / B E = v B = ( )(8.5 0 ) = (c) (i) Undeviated Undeviated (iii) Curve pat upwards (circular pat not accepted) (d) OR OR 6 (a) In a p-n junction, electron-ole recombination forms an internal electric field wic opposes furter diffusion of bot electrons and oles across a region known as te depletion region. Wen a potential difference is applied across suc tat p-type is at a iger potential tan n-type (or in forward bias/p-type connected to positive terminal), te widt of te depletion region is decreased so oles and electrons are allowed to flow troug allowing conduction to occur. Wen te potential difference is applied suc tat n-type is at a iger potential tan te p-type, (or in reversed bias/n-type connected to positive terminal), te depletion region is increased wic prevents te flow of carge carriers across te region, and te p-n junction beaves as a very ig resistance. Tis allows te p-n junction to act as a rectifier as current is allowed to flow in one direction and not te oter. River Valley Hig Scool Pg 4 of 9 Year 6 H Pysics 9646 Preliminary Examinations II 06

5 06 River Valley Hig Scool Prelim Paper Mark Sceme Wen temperature increases for intrinsic semiconductor, electrons are excited from valence band to conduction band and oles are formed in valence band. Te increases in carge carriers are electrons in conduction band and oles in valence band and tese elp to lower te resistance in te material. Te conduction band of metal is partially filled wit electrons. Wit termal excitation, tere is negligible effect on number density of te electrons. Instead, tere is increase in lattice vibrations in te material wic results in iger resistance in metal. 7 (a) (i) B H. Te ratio of B/H decreases wit increasing values of B, taking points from curve A. So te magnetic permeability of iron decreases. NA( B 360 Wb B ) (40000)(0.090)( ) [C] [] (iii) ΔΦ Δt / 50 4 V (sf) [C] [] (i) [] B max / T P / kw lg (B max / T) lg (P / W) Fig. 7.4 River Valley Hig Scool Pg 5 of 9 Year 6 H Pysics 9646 Preliminary Examinations II 06

6 06 River Valley Hig Scool Prelim Paper Mark Sceme lg (P / W) 3.80 anomalous (iii) 3.60 Gradient = translate down by lg (B max / T) Fig. 7.5 Correct computation of data in table Correctly plotted point lgp lgk gradient n f nlgb y intercept lgkf Correctly drawn best fit line y y gradient x x n.6 max [4] lgk f K y lgk f (.5995) x J T.6 [C] River Valley Hig Scool Pg 6 of 9 Year 6 H Pysics 9646 Preliminary Examinations II 06

7 06 River Valley Hig Scool Prelim Paper Mark Sceme (iii) Same gradient straigt line Sifted down by 0.30 * [] * lgp lgkf nlgbmax y - intercept is lgk f, or (lgk ten intercept w illbecome (lgk (lgk lgf lg ) (lgk lgf ) soif f is alved, lg f ) lgf 0.30) (c) (i) Read off from grap, at B max = 0.0, P loss =.30 kw [] (iii) Average power supplied to primary coil = (4500)(0)(0.5) = 500 W [C] efficiency % Average power supplied to secondary coil = =000 W V rms (sec ondary ) ( ) V [C] P P loss I R ( ) R V 000 ( ) (0) W It is an overestimate as it does not factor in oter losses, suc as copper loss in te resistance of te wires, or eddy currents in te iron core. [] [] River Valley Hig Scool Pg 7 of 9 Year 6 H Pysics 9646 Preliminary Examinations II 06

8 06 River Valley Hig Scool Prelim Paper Mark Sceme Q8 Planning Markseme ( marks) Diagram: [ mk] Lamp connected to constant power source pieces of glass supported by older Potocell connected to voltmeter V fixed distance [Labelled diagram of apparatus: lamp, glass seet and potocell in line. Voltmeter connected in parallel to potocell] (a) te identification and control of variables, [ mk] n is te independent variable and E is te dependent variable control includes distance from ligt to potocell kept constant, intensity of ligt kept constant, constant voltage across lamp/current troug lamp/brigtness (any control) Do not allow same lamp/output. te equipment you would use, Use micrometer screw gauge to measure tickness of glass seet Voltmeter to measure emf [ mk] (c) te procedure to be followed, [3 mk] Take at least readings of tickness of glass and find average Direct ligt at glass, read emf E of potocell Record n and E, repeat wit additional piece of glass Additional detail [any oter point] Preliminary readings: adjust distance of lamp, glass and detector until noticeable reading is obtained on voltmeter. Try a few pieces of glass to get te suitable range of tickness suc tat tere is significant reading on te voltmeter. Use small distance/ig intensity to gain large reading. Metod to ceck output of lamp is constant e.g. measure current troug/p.d. across lamp/regularly ceck V0 wit no glass. Clean seets of glass before use. Direction of ligt is perpendicular to glass seets/constant orientation. River Valley Hig Scool Pg 8 of 9 Year 6 H Pysics 9646 Preliminary Examinations II 06

9 06 River Valley Hig Scool Prelim Paper Mark Sceme Do not allow vague computer metods. (d) ow te absorption coefficient is determined from your readings, ln E = αnt + ln E 0 Plot a grap of ln E against n. (Allow ln E against nt) [ mk] From grap, calculate gradient α = ( )gradient / t. (ln E against nt ten α = ( )gradient) (e) any precautions tat would be taken to improve te accuracy and safety of te experiment. [ mk] Perform experiment in a dark room or sield apparatus from ambient ligt Reasoned metod to prevent burns from ot source, e.g. use gloves Reasoned metod to prevent eye damage from brigt/intense source, e.g. sield lamp/ dark glasses/do not look at source directly Reasoned metod to prevent cuts from glass e.g. use gloves. River Valley Hig Scool Pg 9 of 9 Year 6 H Pysics 9646 Preliminary Examinations II 06