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GCE MAY 2007 : A2 3B Experimental and Investigative Skills (Session 2)

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Centre Number 71 Candidate Number ADVANCED General Certificate of Education 2007 assessing Module 6: Experimental and Investigative Skills Session No. 2 A2Y33 Physics Assessment Unit A2 3B [A2Y33] TUESDAY 22 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 2 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 2 3 Total Marks A2Y3BaS7 3035 Marks Instructions to Candidates Answer all the questions in this paper, using 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, and after 26 minutes you must stop using the apparatus in Questions 1 and 2 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(b). 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. Question 3 contributes to the synoptic assessment of the Specification. In this question, you will need to make and use connections between different areas of physics and to use your knowledge and understanding of more than one area. A2Y3BaS7 3035 2 [Turn over 1 Introduction In this experiment you will time the oscillations of a 100 cm rule balanced on top of cylinders of different diameters. You will investigate how the periodic time of the oscillations depends on the diameter of the cylinder. Aims The aims of this experiment are (a) to measure the period of the oscillating rule for various diameters of the cylinder, (b) to analyse the results and plot a linear graph, (c) to use this graph to find the value of an unknown constant. Apparatus You are provided with five cylinders of different diameters, a 100 cm rule, vernier calipers, a micrometer screw-gauge and a stop watch. Rule b Bench Cylinder D Fig. 1.1 A2Y3BaS7 3035 3 [Turn over Procedure Examiner Only Marks Remark (a) (i) Use the micrometer screw-gauge to determine the average thickness b of the 100 cm rule. Record your results in Table 1.1. (ii) Use the vernier calipers to measure the external diameter D of each of the cylinders. You may need to use the base of the cylinder. Record your results in Table 1.2. (iii) Secure the largest cylinder to the bench with Blu-tack. Set the 100 cm rule on the cylinder and set it oscillating with a small amplitude, as shown in Fig. 1.1. Take measurements to determine the period of oscillation T. Take care not to use too large an amplitude; the rule may slide off the cylinder. Record all your readings, including the value of T, in Table 1.2. Repeat this procedure for the other four cylinders. Results (b) (i) Use Table 1.1 to record measurements that will allow you to calculate the average thickness b of the rule. Table 1.1 Thickness/mm Average thickness b = _________ mm (ii) Complete the column headed (D b) in Table 1.2. [2] [1] Use the other columns of Table 1.2 to record measurements that will allow you to calculate the periods of oscillation T of the rule. [6] Table 1.2 D/mm A2Y3BaS7 3035 (D b)/mm Period T/s 4 [Turn over Theory Examiner Only Marks Remark The relationship between the period T and the diameter D is given by T 2 = A(D b)n Equation 1.1 where A and n are constants. Analysis (c) You are to draw a suitable straight-line graph and use it to find the constant n. To do this requires a log log graph. (i) Take logarithms of the right-hand side of Equation 1.1 and complete Equation 1.2 below. log10 (T 2) = _____________________ Equation 1.2 [1] By comparing Equation 1.2 with the general equation for a straight line graph y = mx + c, (ii) state the quantities you intend to plot on your graph, Vertical axis: __________________________________________ Horizontal axis: _____________________________________ [2] (iii) state how the value of n may be obtained from this graph. __________________________________________________ [1] A2Y3BaS7 3035 5 [Turn over (iv) In order to plot this graph you will need to calculate the values of further quantities from your results. Record the values of your chosen quantities in Table 1.3. The first two columns of the table have already been headed for you. Head the third column appropriately. [4] Examiner Only Marks Remark Table 1.3 T 2/s2 log10 (T 2/s2) (v) Label the axes of the graph grid of Fig. 1.2 and choose suitable scales. Plot the points and draw the best straight line through them. [5] (vi) Use your graph to find the value of the constant n. Record the value below. n = ___________ A2Y3BaS7 3035 [3] 6 [Turn over Fig. 1.2 A2Y3BaS7 3035 7 [Turn over 2 Introduction In this experiment you will obtain the current-voltage characteristic of a non-ohmic device called a light-emitting diode (LED). Aims The aims of the experiment are (a) to set up a circuit to obtain values of current and voltage for an LED, (b) to use the circuit to obtain the current-voltage characteristic for a green-emitting LED, (c) to use the characteristic to obtain quantitative information about the electrical behaviour of the LED. Apparatus You are provided with a green-emitting LED with the positive lead marked. Also supplied are a 6 V power supply, a potentiometer (potential divider) unit, a digital voltmeter, a digital ammeter, a safety resistor labelled S and connecting leads. A2Y3BaS7 3035 8 [Turn over Procedure (a) Set up the circuit shown in Fig. 2.1. potentiometer + T3 power supply A knob S V T1 LED + T2 Fig. 2.1 Examiner Only Marks Remark The lead on the LED marked + must be connected as shown. The diode will not light if incorrectly connected. When you have set up the circuit, turn the potentiometer knob fully anticlockwise. Test the circuit by switching on the power supply and turning the potentiometer knob clockwise so as to obtain a current through the diode and then to gradually increase the current. Stop turning the potentiometer knob when you reach a current of about 18 mA. The diode should emit green light. [3] If you are unable to obtain a working circuit, ask the Supervisor for assistance. A deduction of 3 marks will be made. A2Y3BaS7 3035 9 [Turn over (b) Return the potentiometer to the fully anti-clockwise position. Take a series of readings of the current I through the LED, up to a maximum of about 18 mA, and the corresponding voltage V across the LED. Note that the characteristic is non-linear in the low-current region. It is important to take plenty of readings in this region, making sure that you go down to currents of 0.1 mA or less. Record your results in Table 2.1. [4] Examiner Only Marks Remark Results (c) Table 2.1 I/mA V/V I/mA V/V Analysis (d) (i) You are to plot a graph of I against V on the graph grid of Fig. 2.2. Label the axes of the graph grid and choose suitable scales. It is not necessary to start the voltage axis from zero. It is advisable to make your graph as large as the graph grid will allow. [5] A2Y3BaS7 3035 10 [Turn over Fig. 2.2 A2Y3BaS7 3035 11 [Turn over (ii) In testing these diodes, the manufacturer takes a current of 0.2 mA to indicate that the LED is emitting light, or is on . Read off from your graph the value of the voltage Von across the LED at which the current is 0.2 mA. Von = ___________ V Examiner Only Marks Remark [1] (iii) (1) From your graph, determine the rate of change of current with voltage when the current is 2.0 mA. State this quantity, with its unit if applicable, below. If the quantity does not have a unit, state no unit . Rate of change = ____________________ Unit: ____________________ [4] (2) On Fig. 2.3, sketch a graph to show how the rate of change of current with voltage depends on the voltage V across the LED over the full range of voltages. You do not need to obtain further numerical values. [2] Rate of change of current with voltage 0 0 V/V Fig. 2.3 A2Y3BaS7 3035 12 [Turn over (iv) The manufacturer considers that the LED is at its normal brightness when the current through it is 15 mA. Using the equation P = VI, calculate the electrical power of the diode when it operates at normal brightness. Use your graph to obtain additional information required. Power = _________ mW Examiner Only Marks Remark [2] (v) Digital meters flicker (that is, the last digit on the display changes randomly) during the course of taking readings. The magnitude of this flicker can be taken as a measure of the uncertainty in a reading. Assume that the electrical power of the diode at normal brightness is being measured from a single value of the current (15.0 mA) and the corresponding value of the voltage. These values are obtained using digital meters. The flicker in the current and voltage readings is 0.1 mA and 0.01 V respectively. Calculate the percentage uncertainty in the value of the power, due only to the flicker of the readings. Percentage uncertainty = _________ % A2Y3BaS7 3035 13 [4] [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 in part (b). 3 Examiner Only Marks Remark Planning and design question Introduction In this question you are asked to discuss the details of an experiment to find a value for the viscosity of a clear, thick liquid called glycerin by dropping ball bearings through a transparent cylinder full of the liquid. Viscosity is the internal property of fluids that makes flow difficult it is fluid friction. The maximum velocity attained by an object in free fall is called the terminal velocity and is strongly affected by the viscosity of the fluid through which it is falling. When terminal velocity is attained, the body experiences no acceleration, so the forces acting on the body are in equilibrium. In this experiment, the state of terminal velocity is very quickly attained. However, the speed of descent does not remain constant near the bottom of the cylinder. (a) Theory The viscosity of a fluid is given by = kr 2/v where r is the radius of the ball bearing v is the terminal velocity of the ball bearing falling through the glycerin, k is a known constant. (i) In the experiment you will need to determine values for r and v. By plotting a suitable graph, you will then find the value of . Label the axes below and sketch the shape of graph you would expect to obtain. A2Y3BaS7 3035 14 [Turn over (ii) Explain how you would use your graph to find a value for . Remember, k is a known constant. Examiner Only Marks Remark _____________________________________________________ _____________________________________________________ __________________________________________________ [2] (iii) Use your answer to (a)(ii) to obtain a unit for . The SI unit for k is kg m 2 s 2. Unit for = _______________________ [2] (b) Planning and design procedure You are provided with five ball bearings of different sizes all made from the same material. Their diameters vary between about 2 mm and 12 mm. (i) Name a suitable measuring instrument and explain how you will obtain a precise and reliable value for the radius r of each ball bearing. _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ __________________________________________________ [4] A2Y3BaS7 3035 15 [Turn over (ii) Write an account of the experiment you would carry out to measure the terminal velocity of the ball bearings as they fall through the glycerin. Remember, the terminal velocity is attained very quickly and the speed is not constant near the bottom of the cylinder. Your account should include (1) a description of the procedure, (2) a list of readings to be taken and (3) how the readings are used to obtain a value for terminal velocity. Examiner Only Marks Remark You may use the space below for a diagram to illustrate your answer. _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ __________________________________________________ [6] Quality of written communication A2Y3BaS7 3035 [1] 16 [Turn over (c) Interpretation Examiner Only Marks Remark The viscosity of a fluid is temperature dependent. At 40 C the viscosity of glycerin is 280 units At 20 C the viscosity of glycerin is 1420 units (i) State qualitatively what happens to the time taken by the ball bearing to fall through the glycerin as the temperature of the glycerin decreases. Explain your answer. _____________________________________________________ _____________________________________________________ __________________________________________________ [2] (ii) Assuming a linear relationship between viscosity and temperature in the range stated above, calculate the numerical value of the viscosity at 25 C. Viscosity = ___________________ units [1] THIS IS THE END OF THE QUESTION PAPER A2Y3BaS7 3035 17 [Turn over A2Y3BaS7 3035 18 [Turn over A2Y3BaS7 3035 19 [Turn over S 12/06 7-148-1

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Additional Info : Gce Physics May 2007 Assessment Unit A2 3B, Module 6: Experimental and Investigative Skills (Session 2)
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