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GCE MAY 2008 : A2 3B Experimental and Investigative Skills (Session 1)

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Centre Number 71 Candidate Number ADVANCED General Certificate of Education 2008 assessing Module 6: Experimental and Investigative Skills Session No. 1 A2Y32 Physics Assessment Unit A2 3B [A2Y32] MONDAY 19 MAY TIME 1 hour 30 minutes. INSTRUCTIONS TO CANDIDATES Write your Centre Number and Candidate Number in the spaces provided at the top of this page. Turn to page 2 for further Instructions and Information. For Teacher/Supervisor s use only Question 1 Procedure (a) Was the candidate given the pre-connected circuit, or was assistance given in the connection of the candidate s circuit? YES NO For Examiner s use only Question Number 1 Procedure (b) Was the candidate given the pre-connected circuit, or was assistance given in the connection of the candidate s circuit? A2Y3BS8 4190 YES NO 2 3 Total Marks Marks Instructions to Candidates Answer all the questions in this booklet. Rough work and calculations must also be done in this booklet. Except where instructed, do not describe the apparatus or experimental procedures. The Supervisor will tell you the order in which you are to answer the questions. Not more than 28 minutes are to be spent in answering each question. In Questions 1 and 2 you must stop using the apparatus after 26 minutes so that it can be re-arranged for the next candidate. At the end of the 28-minute period you will be instructed to move to the area set aside for the next question. At the end of the Test, a 6-minute period will be provided for you to complete your answer to any question, but you will not have access to the apparatus during this time. Information for Candidates The total mark for this paper is 70. Quality of written communication will be assessed in Question 3. Questions 1 and 2 carry 25 marks each, and Question 3 carries 20 marks. Figures in brackets printed down the right-hand side of pages indicate the marks awarded to each part question. A2Y3BS8 4190 2 [Turn over 1 Introduction In this experiment you will investigate the variation of current with time for the charging of two different capacitor circuits. Aims The aims of this experiment are (a) to connect a circuit to charge a capacitor through a resistor, (b) to plot a graph from the experimental results, (c) to use the graph to determine the resistance of the resistor, (d) to use the circuit to find the capacitance of a second, unknown capacitor. Apparatus You are provided with a d.c. supply, a digital microammeter, a capacitor of known capacitance, a capacitor of unknown capacitance, a resistor, a switch, a stopwatch and some connecting leads. Two of the connecting leads are green, and with the switch are to be used as a shorting lead for the capacitor. CAUTION: before you open the switch on the shorting wire, the Supervisor must check your circuit. There is no mark penalty for this check. A2Y3BS8 4190 3 [Turn over Procedure (a) Examiner Only Marks Remark Connect the components as shown in the circuit of Fig. 1.1. Note that the capacitor polarity should be as shown. Do not use the unknown capacitor C2 at this stage. d.c. supply shorting wire C1 R closed switch A Fig. 1.1 If you are unable to set up this circuit, ask the Supervisor for assistance. A deduction of 2 marks will be made. [2] You are to obtain a series of readings of current I at ten-second intervals for one minute. Open the switch on the green shorting wire and record your results in Table 1.1. Results Table 1.1 t/s 0 10 20 30 40 50 60 I/ A [6] Analysis When a capacitor of capacitance C charges through a resistor of resistance R, the current I in the resistor varies with time t according to the equation I = I0 e t CR Equation 1.1 where I0 is the initial current. (a) On the grid of Fig. 1.2 draw a graph of I against t. Choose suitable scales, plot the points and draw a smooth curve through them. [5] A2Y3BS8 4190 4 [Turn over Fig. 1.2 A2Y3BS8 4190 5 [Turn over (b) The current I in the resistor varies according to Equation 1.1. Examiner Only Marks Remark The time constant CR (= ) is equal to the time taken for the current to decay to 37% of its initial value. (i) Use your graph to determine the time constant C1R. Show clearly the readings used. Enter the value, with an appropriate unit, below. C1R = __________________ Unit: ___________________ [4] (ii) The capacitance C1 of the capacitor in the circuit is 1000 F. Deduce the value of the resistance of the resistor. R = ___________________ [2] Procedure (b) Connect the second capacitor C2, which is of unknown capacitance, into the circuit in parallel with the capacitor C1 as shown in the circuit of Fig. 1.3. Again note that it is important to connect the capacitor with polarity as shown. d.c. supply shorting wire C2 C1 R closed switch A Fig. 1.3 If you are unable to set up this circuit, ask the Supervisor for assistance. A deduction of 1 mark will be made. A2Y3BS8 4190 6 [1] [Turn over Obtain a series of readings of current I at ten second intervals for one minute. Open the switch on the green shorting wire and record your results in Table 1.2. Examiner Only Marks Remark Results Table 1.2 t/s 0 10 20 30 40 50 60 I/ A [2] On the same axes of Fig. 1.2, plot the points from Table 1.2 and draw a smooth curve through them. (a) Find the value of the time constant 2 of this second circuit from the graph. Enter the value, with an appropriate unit, below. 2 ___________________ [1] (b) Use this value of the time constant 2 , the capacitance C1 and your value of the resistance R to find the capacitance C2 of the unknown capacitor. Show clearly how you determined the value. C2 = ___________________ A2Y3BS8 4190 [2] 7 [Turn over 2 Introduction Examiner Only Marks Remark In this experiment you will investigate the oscillations of a laboratory beaker suspended from a spring. Aims The aims of the experiment are (a) to measure the length of a spring when loads are attached to it, (b) to determine the period of oscillation of the system, (c) to illustrate the relationship between the period of oscillation and the length of the spring by plotting a straight line graph, (d) to use the results to determine the value of a constant. Apparatus You are provided with a spring which is attached to a clamp on a retort stand, a 250 cm3 laboratory beaker with a string handle, a beaker of water, a measuring cylinder, a stopwatch and a half-metre rule. There is a 100 g mass at the bottom of the beaker to provide stability. Leave this in the beaker at all times. The beaker has been attached to the spring which is suspended from a retort stand, as shown in Fig. 2.1. L Fig. 2.1 A2Y3BS8 4190 8 [Turn over Procedure Examiner Only Marks Remark Determine the length L of the spring with the beaker and the slotted mass attached, as shown in Fig. 2.1. Record this length in Table 2.1. Displace and release the beaker gently so that it oscillates vertically with a small amplitude. Take readings to allow you to determine the period of oscillation T. Complete any headings needed in Table 2.1 and record your observations. Measure 50 cm3 of water using the graduated cylinder and add the water to the suspended beaker. Determine and record the new values of L and T with this mass of water of 50 g. Repeat the procedure by adding 50 cm3 each time, determining corresponding values of L and T, up to 200 g of water. Results Table 2.1 Volume of water/cm3 0 50 100 150 200 Mass of water/g 0 50 100 150 200 L /m T /s [6] Theory Theory suggests that the relationship between T and L is given by T = 2 L P Q Equation 2.1 where P and Q are constants. A2Y3BS8 4190 9 [Turn over (a) You are to draw a suitable straight line graph which may be used to find the values of the constants P and Q. Examiner Only Marks Remark (i) (1) Modify Equation 2.1 by squaring both sides to give Equation 2.2. Equation 2.2 [1] (2) Compare Equation 2.2 with the equation of a straight line y = m x + c and state the quantities you intend to plot on your graph. Vertical axis: __________________________ Horizontal axis: ________________________ [2] (ii) Explain how the constants Q and P could be obtained from your graph. ______________________________________________________ ____________________________________________________ [2] (iii) In order to plot this graph, you may need to calculate the values of a further quantity. If so, head the last column in Table 2.1 appropriately, carry out the calculations and tabulate the results in this column. [2] (iv) Label the axes of the graph grid of Fig. 2.2 and choose suitable scales. Plot the points and draw the best fit straight line through them. [5] (v) Use the graph to find the value of Q and enter the value below with the correct unit. Q = ____________________ [2] (vi) Q is the acceleration of free fall, which is normally stated as 9.81 m s 2. Calculate the percentage difference between your value of Q and the stated value. Percentage difference = ____________________ % A2Y3BS8 4190 10 [1] [Turn over (b) Consider the experiment you have completed and suggest two sources of error which may arise in such a practical procedure, and how they may be reduced. Examiner Only Marks Remark 1. Error ___________________________________________________ Method of reduction _________________________________________ __________________________________________________________ 2. Error ___________________________________________________ Method of reduction _________________________________________ _______________________________________________________ [4] Fig. 2.2 A2Y3BS8 4190 11 [Turn over Where appropriate, your answer to this question should be in continuous prose. You will be assessed on the quality of your written communication. 3 Examiner Only Marks Remark Planning and design question Introduction Traditionally, bronze 2 p British circulation coins were made from an alloy of copper, tin and zinc. However, in 1992 the Royal Mint changed the material of these coins to copper-plated steel. d t 2 p coin Fig. 3.1 In this question you are to discuss a plan to find the density of a pre-1992 2p coin and a post-1992 2p coin. The density of a material may be calculated using the equation mass density = volume Equation 3.1 It is proposed to measure the mass of each coin with a top-pan balance. (a) The volume V of a disc of diameter d and thickness t can be determined using Equation 3.2. 1 V = d 2t 4 Equation 3.2 (i) Suggest an appropriate instrument which may be used to measure the thickness of the coins with precision. Give the uncertainty in measurements made with this instrument. Instrument __________________ Uncertainty = _______________ A2Y3BS8 4190 [1] [1] 12 [Turn over (ii) (1) What feature of a coin makes the measurement of the thickness uncertain? Examiner Only Marks Remark ________________________________________________ [1] (2) Suggest how you would take this feature into account when taking measurements. ________________________________________________ [1] (iii) The vernier caliper is an appropriate instrument for the measurement of the diameter of this coin. (1) State the uncertainty in the measurement taken with this instrument. Uncertainty = _____________________________________ [1] (2) Explain why the measurement of this quantity will have a greater influence on the error in the calculation of density. ___________________________________________________ ________________________________________________ [1] (iv) Briefly describe another procedure to measure the volume of a coin. State one source of uncertainty. State also how this method may be improved upon. ______________________________________________________ ______________________________________________________ ______________________________________________________ ____________________________________________________ [2] A2Y3BS8 4190 13 [Turn over (b) Suppose that a top-pan balance is not available for measuring the mass of the coins. It is proposed that the mass of the coins should be determined using the concept of centre of gravity, the principle of moments and the following apparatus: several coins of each type, a metre rule of known mass and a knife edge pivot. Examiner Only Marks Remark (i) State the principle of moments. ______________________________________________________ ____________________________________________________ [1] (ii) Draw a labelled diagram and describe a procedure using the principle of moments and the apparatus listed above to find the mass of the coins. ______________________________________________________ ______________________________________________________ ______________________________________________________ ____________________________________________________ [5] A2Y3BS8 4190 14 [Turn over (c) With the change in material came a change in density of the coins. The post-1992 coins are 9% less dense than the pre-1992 coins. For sorting and counting purposes at banks, it is important that all 2 p coins in circulation have the same mass and diameter. Hence the thickness of the coins had to change when the material they were made from changed. The pre-1992 coins have a thickness of 1.85 mm. What thickness must the post-1992 coins be to keep the mass and diameter constant? Thickness of post-1992 coin = __________________ mm Examiner Only Marks Remark [3] (d) Copper-plated coins are the same mass, colour, diameter and design as those made of bronze and circulate alongside them. Apart from differences in density and thickness, there is one other notable difference which makes the two types easy to separate by a simple item of school laboratory apparatus. What is this item, and why can it be used to separate pre-1992 and post-1992 coins? __________________________________________________________ __________________________________________________________ _______________________________________________________ [2] Quality of written communication [1] THIS IS THE END OF THE QUESTION PAPER A2Y3BS8 4190 15 [Turn over S 11/07 529-048-1

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Additional Info : Gce Physics May 2008 Assessment Unit A2 3B, Module 6: Experimental and Investigative Skills
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