General Certificate of Education Advanced Subsidiary Examination June 2014 Physics PHA3/B3/XTN (Specifications A and B) Unit Investigative and Practical Skills in AS Physics Route X Externally Marked Practical Assignment (EMPA) Teachers’ Notes Confidential The Exams Officer should make two copies of these Teachers’ Notes; one copy for the Head of A-level Physics and one for the technician These copies can be released to the Head of A-level Physics and the technician at any point following publication but must be kept under secure conditions at all times Teachers can have sight of the Teachers’ Notes but no further copies should be made Estimated entries must be submitted to AQA in order for centres to receive hard copies of the materials to be used by candidates WMP/Jun14/PHA3/B3/XTN/E8 PHA3/B3/XTN For Section A Task 1, Question Candidates are to investigate the extension of a mass-spring system Having calibrated the springs, they are to incorporate these in a system of coplanar forces to determine the value of an unknown mass Apparatus required: • two expendable steel springs, coupled together • mass hanger of mass 100 g; five additional 100 g slotted masses • concealed mass labelled ‘mass U’ consisting of a mass hanger and slotted masses to total 340 g; the hook of the mass hanger should be accessible so that the mass can be suspended from the loop on the string • retort stand to be fitted with a boss about 300 mm above the bench to which a clamp is fixed; the base should be made secure with a G-clamp • retort stand to be fitted with a boss, the height of which can be adjusted up to 500 mm above the bench; a free-running pulley is to be fixed to this boss so that the axis of rotation of the pulley is parallel to the bench – it is suggested that a counterweight (or other means) be provided to prevent this stand from sliding or toppling when candidates carry out question (a)(iii) • about 600 mm of string • half metre ruler and set-square • one sheet of A4 plain paper; Sellotape or Blu-Tack as required to stick this to the bench • pencil Link one end of the coupled springs through the arm of the clamp before fitting this to the boss, thus ensuring that the springs cannot slip off Set the height of the clamp at about 300 mm above the bench with the arm of the clamp perpendicular to the edge of the bench Use a G-clamp to secure the base of this stand to the bench Candidates are instructed not to move this stand or adjust the height of the clamp to which the springs are attached Tie the string to the free end of the springs then fasten a small loop about cm from this point Make an ink mark on the string at roughly the midpoint of the string between the spring and the loop Pass the string over the pulley then fasten the mass hanger securely to the free end Candidates are instructed not to unfasten the string from the mass hanger and Supervisors should be vigilant that they adhere to this Cut the sheet of paper into two lengthways and arrange the piece end to end to create a strip of about 100 mm wide and 580 mm long Tape or Blu-Tack this to the bench so that it will lie below the horizontal part of the string during part (a) of the experiment Arrange the apparatus as shown below and place all the other equipment on the bench in clear view of the candidate boss R ink mark on the string loop clamp L stand L G-clamp not shown stand R mass hanger At changeover replace the sheet of paper for the next candidate Examiners require no information for this question WMP/Jun14/PHA3/B3/XTN counterweight not shown The following data are provided to assist in trialling the practical tasks Question 1 (a) (i) (a) (iv) (d) (i) h/mm = 270 m/g x/mm 200 600 331 xU/mm = 141 Turn over ᮣ For Section A Task Candidates will investigate how the pd across a power supply varies when the resistance of the external circuit is changed Apparatus required for each candidate for the circuit: • digital voltmeter, or a 3½ digit multimeter, capable of reading to 0.01 V or better • two connecting leads terminating at mm plugs to connect the voltmeter in the circuit • dc power supply, one or more dry cells in holder are adequate, pd at discretion of centre to suit the range of voltmeter to be provided (a single D-type cell in a holder is suitable if the voltmeter is set for full scale reading of V/ 2000 mV) • 10 Ω resistor (0.5 W or 0.6 W, carbon or metal film) should be wired in series with the positive terminal of the power supply; to avoid confusion this resistor should be concealed from the view of the candidate • two mm round sockets labelled ‘P’ and ‘N’ to be connected to the free end of the 10 Ω resistor and the negative terminal of the dc power supply respectively (see circuit diagram below) • one 120 Ω resistor (0.5 W or 0.6 W, carbon or metal film) the value of this resistor is to be concealed from the candidate; this resistor should be labelled ‘resistor X’ and placed in clear view for the candidate to see • resistors of resistance 39 Ω, 68 Ω and 47 Ω, (all 0.5 W or 0.6 W, carbon or metal film) wired in series, as per the diagram below • SPST switch, toggle type, labelled ‘S’ with ‘open’ and ‘closed’ positions marked • two short leads terminating at crocodile clips to serve as flying leads (see diagram and explanation below); these leads should be made using insulated stranded wire, not solid-core wire • strip-board, solder pins and connecting wire, as required to complete the connection of the 10 Ω resistor in series with the positive terminal of the power supply for construction of the mounted resistors: • terminal block: four 2-way terminal blocks (eg cut from A or A 12-way terminal block) • screws • rectangular piece of softwood on which to mount circuit The circuit, which should be connected ready for each candidate, is shown below round socket labelled P switch S round socket labelled N concealed 10 Ω resistor 39 Ω flying lead 68 Ω 47 Ω flying lead The 10 Ω resistor should be wired in series with the positive terminal of the power supply; the resistor should then be concealed from view, eg by positioning it alongside the cell holder and winding insulation tape around it WMP/Jun14/PHA3/B3/XTN The mounting of the resistors and flying leads can be accomplished using the 2-way terminal blocks, screwed to a rectangular piece of softwood, as shown in the diagram below Labels, showing the values of the resistors, can be stuck on the wood, as shown 39 Ω 68 Ω 47 Ω The length of the flying leads should enable each lead to be connected across (and thus shorting out) the resistor to either side so that between sockets P and N a series circuit with any permutation of the 39 Ω, 68 Ω and 47 Ω resistors can be produced Note that it is not possible to use the flying leads to short out all three resistors simultaneously and no additional leads should be made available that might enable the candidate to this Candidates will vary the external resistance of the circuit by using the flying leads singly or in combination For example, when one flying lead is connected across the 47 Ω resistor the external resistance between sockets P and N is a series combination of 39 Ω and 68 Ω The candidates will be expected to deduce that the circuit resistance for this circuit is 107 Ω; the Supervisor must not provide the candidates with any assistance in making this deduction 39 Ω 68 Ω 47 Ω flying lead connected in parallel with the 47 Ω resistor Turn over WMP/Jun14/PHA3/B3/XTN ᮣ The candidates will also be required to connect resistor X in parallel with the 68 Ω resistor This can be achieved using both the flying leads, eg 39 Ω 68 Ω 47 Ω resistor X Testing: With S open the voltmeter should read the emf of the supply When S is closed and resistor X is in parallel with the 68 Ω resistor as shown above, the voltmeter voltmeter reading with S open reading will fall such that the ratio, –––––––––––––––––––––––––– is between 1.06 and 1.10 voltmeter reading with S closed Examiners require no information for this question The following data is provided to assist in trialling the practical tasks Question 1 (a) (i) ε/V = 1.528 (a) (ii) VX/V = 1.411 (b) R1+R2+R3 in series WMP/Jun14/PHA3/B3/XTN R/Ω V/V 154 1.428 General Certificate of Education June 2014 Advanced Subsidiary Level Examination PHYSICS (SPECIFICATIONS A AND B) PHA3/B3/XTN Unit SUPERVISOR’S REPORT When completed by the Supervisor, this Report must be attached firmly to the attendance list, or in the case of any problem affecting a particular candidate, it should be attached to the candidate’s script, before despatch to the Examiner Information to be provided by the centre Section A Task Question No information is required Section A Task Question No information is required Details of problems encountered by candidate candidate number Supervisor’s Signature Centre Number Date Centres may make copies of this Supervisor’s Report for attachment to individual scripts where necessary WMP/Jun14/PHA3/B3/XTN The following instructions include the task that candidates will be required to complete in Section A Task and Section A Task These instructions not include all the questions that may be asked Section A Task 1 (a) You are to investigate the extension of a mass-spring system You are provided with the apparatus shown in Figure Figure boss R loop clamp L stand R mass hanger Te ac he ru se G-clamp not shown stand L on ly ink mark on the string counterweight not shown Stand L has been clamped to the bench and a mass hanger has been securely fastened to the free end of the string An ink mark has been made on the string between the end of the spring and the loop tied in the string You must not move stand L, or adjust the height of clamp L, or unfasten the string from the mass hanger during the experiment WMP/Jun14/PHA3/B3/XTN (a) (i) Add mass to the hanger so that m, the total mass fastened to the string, is 200 g Move stand R to the right until the hanger is lifted clear of the bench Adjust the height of boss R until the part of the string between the spring and the pulley is horizontal, as shown in Figure Check that the system is in equilibrium Figure ink mark boss R h m = 200 g Te ac he ru se point O marked on the strip of paper on ly loop Measure and record h, the vertical distance between the horizontal part of the string and the table h = (a) (ii) A point has been marked on the string between the end of the spring and the loop; a strip of paper has been taped to the bench below the horizontal part of the string Mark the point O on the strip of paper directly below the ink mark Question continues on the next page Turn over WMP/Jun14/PHA3/B3/XTN ᮣ 10 (a) (iii) Add mass to the hanger until m = 600 g Without adjusting the height of boss R, move stand R further to the right until the mass is once again lifted clear of the bench, as shown in Figure Figure boss R at same height ink mark position of point O on ly mark P marked on the strip of paper m = 600 g x stand R moved to the right Te ac he ru se Check that the system is in equilibrium, then mark the point P on the strip of paper directly below the ink mark Mark a straight line joining the points O and P Measure and record x, the distance along the line between O and P x = (a) (iv) Remove mass from the hanger so that m = 500 g If necessary move stand R to the left so that the hanger does not touch the pulley, while remaining clear of the bench Check that the ink mark is directly above the line between O and P Check that the system is in equilibrium then locate the point on OP that is directly below the ink mark then measure and record the new value of x Repeat the procedure until you have the values of x when m = 400 g and m = 300 g Record all your measurements in Table on page WMP/Jun14/PHA3/B3/XTN 11 Measurements Table m/g x/mm 200 600 500 Te ac he ru se 300 on ly 400 Turn over ᮣ WMP/Jun14/PHA3/B3/XTN 12 (d) You are provided with an object U, the mass of which you are to find Suspend U from the loop tied in the string The apparatus will now appear as in Figure Figure ink mark on ly object U suspended from the loop boss R at same height as before Te ac he ru se Add mass to the hanger so that m = 500 g Raise boss R so that both masses are lifted clear of the bench and the part of the string between the spring and the loop is approximately horizontal Make small adjustments to the position of stand R, moving this stand either left or right, until the ink mark is at a height h, as measured in part (a)(i), and is directly over the line between O and P, as shown in Figure Figure boss R raised and stand R moved to the left or to the right, as required ink mark point marked on line between O and P directly below the ink mark object U position of point O h position of point P m = 500 g xU WMP/Jun14/PHA3/B3/XTN 13 (d) (i) Check that the system is in equilibrium then locate the point between O and P that is directly below the ink mark Measure and record the distance xU that is defined in Figure Te ac he ru se on ly xU = Turn over WMP/Jun14/PHA3/B3/XTN ᮣ 14 Section A Task In this experiment you are required to investigate how the potential difference (pd) across a power supply varies when the resistance of the external circuit is changed You are provided with the circuit shown in Figure Figure P N switch S 47 Ω flying lead Te ac he ru se flying lead 68 Ω on ly 39 Ω (a) Use the leads supplied to connect the voltmeter between socket P and socket N (a) (i) Ensuring that switch S is in the open (off) position, read and record the voltmeter reading ε, which is the electromotive force (emf) of the power supply ε = WMP/Jun14/PHA3/B3/XTN 15 (a) (ii) You are provided with a resistor X, the resistance of which has been concealed Use the flying leads to connect resistor X in parallel with the 68 Ω resistor, as shown in Figure Figure 39 Ω 68 Ω 47 Ω on ly resistor X Close (turn on) switch S then read and record Vx , the new voltmeter reading Te ac he ru se Vx = Turn over ᮣ WMP/Jun14/PHA3/B3/XTN 16 (b) Keeping switch S closed, remove resistor X so that R, the resistance of the circuit between socket P and socket N, is the series combination of the 39 Ω, 68 Ω and 47 Ω resistors You may assume that each flying lead has zero resistance so these can be used individually, or in combination, to change R in a predictable way In the example shown in Figure 10, one flying lead has been connected in parallel with the 47 Ω resistor and R is now the series combination of the 39 Ω and 68 Ω resistors Figure 10 68 Ω 47 Ω on ly 39 Ω the flying lead is shorting out the 47 Ω resistor Te ac he ru se Using neither of the leads, or either lead separately or both leads in combination, obtain values of V that correspond to all possible values of R When you have completed your measurements, open (turn off) switch S Record below all your values of R and V in a single table Note that the independent variable should be recorded in the left-hand column of your table Copyright © 2014 AQA and its licensors All rights reserved WMP/Jun14/PHA3/B3/XTN