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GCE JUN 2007 : AS 3A Medical Physics

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Centre Number 71 Candidate Number ADVANCED SUBSIDIARY (AS) General Certificate of Education 2007 Physics assessing Module 3A: Medical Physics ASY31 Assessment Unit AS 3A [ASY31] FRIDAY 22 JUNE, AFTERNOON TIME 45 minutes. INSTRUCTIONS TO CANDIDATES Write your Centre Number and Candidate Number in the spaces provided at the top of this page. Answer all five questions. Write your answers in the spaces provided in this question paper. INFORMATION FOR CANDIDATES The total mark for this paper is 45. Quality of written communication will be assessed in question 4(c). Figures in brackets printed down the right-hand side of pages indicate the marks awarded to each question or part question. Your attention is drawn to the Data and Formula Sheet which is inside this question paper. You may use an electronic calculator. For Examiner s use only Question Number 1 2 3 4 5 Total Marks ASY3AS7 3037 Marks If you need the values of physical constants to answer any questions in this paper, they may be found on the Data and Formulae Sheet. Examiner Only Marks Remark Answer all ve questions 1 (a) (i) When you move from a bright room to a dark room, the sensitivity of the retina of the eye increases with time. This process is called dark adaptation. Fig. 1.1 shows how the sensitivity of the retina changes during dark adaptation. Sensitivity of retina High dark adaptation Low 0 5 10 15 Time/minutes 20 Fig. 1.1 Explain why retinal sensitivity changes in this way. Your answer should include a reason why the graph has two steps. ______________________________________________________ ______________________________________________________ ____________________________________________________ [2] (ii) Sudden exposure to bright light causes the sensitivity of the retina to change in the process called light adaptation. On the axes of Fig. 1.1 sketch a graph to show the change of sensitivity of the retina during this process. [2] ASY3AS7 3037 2 [Turn over (b) (i) Explain what is meant by the statement that two optical images can be resolved by the human eye. Examiner Only Marks Remark ______________________________________________________ ____________________________________________________ [1] (ii) State one factor upon which the resolving power of the human eye depends. ____________________________________________________ [1] (c) In the constellation of Lyra there is a double star called Epsilon. The two stars making up the double star are 2.41 1014 m apart. These stars are 2.37 1017 m from Earth. (i) Calculate the angular separation of these stars as seen from Earth. Give your answer in degrees. Angular separation = ____________ degrees [2] (ii) The resolving power of the human eye is 9.0 10 3 degrees. Explain whether or not these stars can be seen as separate by an unaided human eye. The stars can be seen as separate cannot be seen as separate Explanation ____________________________________________ ____________________________________________________ [1] ASY3AS7 3037 3 [Turn over 2 A student wears glasses to correct a defect in her vision. The prescription for each eye is the same and is stated as 2.75 D. Examiner Only Marks Remark (a) (i) State the name of the unit symbol D. ____________________________________________________ [1] (ii) What type of lens is in the student s glasses? ____________________________________________________ [1] (iii) State the physical property of the lens to which the prescription refers. ____________________________________________________ [1] (b) (i) State the eye defect from which the student in (a) suffers. ____________________________________________________ [1] (ii) Fig. 2.1 illustrates the student s eye with the uncorrected eye lens. The rays drawn come from an object at the normal near point. In Fig. 2.2 the rays come from a distant object. On Figs 2.1 and 2.2 sketch the rays between the eye lens and the retina. near point retina Fig. 2.1 eye lens retina [2] Fig. 2.2 ASY3AS7 3037 4 [Turn over (c) Determine the position of the student s uncorrected far point. Remember the correcting lens prescription is 2.75 D and a normal eye has a far point at infinity. Uncorrected far point = _____________ m from eye ASY3AS7 3037 5 Examiner Only Marks Remark [3] [Turn over 3 Fig. 3.1, which is not to scale, is a graph of lg10(I/I0) plotted against sound intensity level measured in decibels. Examiner Only Marks Remark 1g10(I/I0) 0 0 sound intensity level/dB Fig. 3.1 (not to scale) (a) Use the defining equation for sound intensity level to state the value of the gradient of this graph. Gradient = _____________ [1] (b) Explain why an increase of intensity of 4.0 10 8 W m 2 sometimes leads to a very large change in intensity level, but sometimes results in almost no change in intensity level. __________________________________________________________ __________________________________________________________ __________________________________________________________ _______________________________________________________ [2] ASY3AS7 3037 6 [Turn over (c) A crowd dispersal system generates a high frequency sound that is audible only to those of teenage years and below. The purpose of this device is to stop groups of teenagers congregating in certain areas by creating an irritating buzzing sound. Examiner Only Marks Remark The device is mounted on a wall. A distance of 1.2 m from it, the intensity level is 75 dB. (i) Calculate the intensity of the sound at this location. Threshold intensity I0 = 1.0 10 12 W m 2. Intensity = __________________ W m 2 [2] (ii) Because the device is mounted on a wall, the sound energy is spread uniformly over the area of a hemisphere of radius 1.2 m. The surface area of a hemisphere = 2 r2. Calculate the energy emitted every second by the source of the sound energy. Your answer must include the relevant SI unit. Energy emitted every second = __________________ SI unit = ________________ ASY3AS7 3037 [3] 7 [Turn over 4 The frequency threshold curve for a small mammal is shown in Fig. 4.1 below. intensity/Wm 2 intensity level/dB 103 150 10 2 100 10 7 50 10 12 0 10 17 50 1 10 100 1000 frequency/Hz 10 000 100 000 Fig. 4.1 Examiner Only (a) (i) State why both intensity and frequency scales in Fig. 4.1 are logarithmic. Marks Remark ______________________________________________________ ____________________________________________________ [1] (ii) State why the intensity level scale in Fig. 4.1 is not logarithmic, but linear. ____________________________________________________ [1] (b) State what is represented by the shaded area on Fig. 4.1. __________________________________________________________ _______________________________________________________ [1] ASY3AS7 3037 8 [Turn over (c) Contrast the hearing of the mammal with that for an adult human. In your answer you should identify: Examiner Only Marks Remark 1. differences in frequency detection, 2. differences in intensity detection. Quote values where possible. __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ _______________________________________________________ [5] Quality of written communication ASY3AS7 3037 [1] 9 [Turn over 5 (a) Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) are powerful diagnostic tools that use computers to produce detailed images of the body. Examiner Only Marks Remark Both techniques require electromagnetic radiation in order to operate. (i) Name the region of the electromagnetic spectrum used in CT scans. ____________________________________________________ [1] (ii) Name the region of the electromagnetic spectrum used in MRI scans. ____________________________________________________ [1] (b) Explain briefly the role played by the electromagnetic radiation in the resonance process of MRI. __________________________________________________________ __________________________________________________________ __________________________________________________________ _______________________________________________________ [2] (c) (i) In ultrasonic imaging a piezoelectric crystal is used both to generate and detect ultrasonic waves. Describe briefly how ultrasonic waves are generated using the piezoelectric effect. ______________________________________________________ ______________________________________________________ ______________________________________________________ ____________________________________________________ [2] ASY3AS7 3037 10 [Turn over (ii) Fig. 5.1 shows the printout from an ultrasound A-scan from an investigation of a patient s eye. Examiner Only Marks Remark s a: b: c: d: e: f: Initial spike (probe tip and cornea) Front lens surface Back lens surface Retina Sclera Orbital fat Ultrasound velocity in lens = 1641 m s 1. Fig. 5.1 Use the data from the A-scan, and associated information above, to calculate the thickness of the eye lens. Thickness of lens = _____________ mm [4] THIS IS THE END OF THE QUESTION PAPER ASY3AS7 3037 11 [Turn over S 1/07 7-157-1

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Additional Info : Gce Physics June 2007 Assessment Unit AS 3A, Module 3A: Medical Physics
Tags : General Certificate of Education, A Level and AS Level, uk, council for the curriculum examinations and assessment, gce exam papers, gce a level and as level exam papers , gce past questions and answer, gce past question papers, ccea gce past papers, gce ccea past papers

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