Cambridge IGCSE Sciences - Co-ordinated (Double) 0654 — 2004 Oct/Nov Paper 3 · Variant 1

This document consists of 24 printed pages. SP (SC/GR) S69776/4 © UCLES 2004 [Turn over UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS International General Certificate of Secondary Education CO-ORDINATED SCIENCES 0654/03 Paper 3 October/November 2004 2 hours Candidates answer on the Question Paper. No Additional Materials are required. READ THESE INSTRUCTIONS FIRST Write your Centre number, candidate number and name on all the work you hand in. Write in dark blue or black pen in the spaces provided on the Question Paper. You may use a soft pencil for any diagrams, graphs, tables or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer all questions. The number of marks is given in brackets [ ] at the end of each question or part question. A copy of the Periodic Table is printed on page 24. Centre Number Candidate Number Name If you have been given a label, look at the details. If any details are incorrect or missing, please fill in your correct details in the space given at the top of this page. Stick your personal label here, if provided. For Examiner’s Use 1 2 3 4 5 6 7 8 9 10 Total www.XtremePapers.com

2 0654/03/O/N/04 1 (a) Fig. 1.1 shows how the radiation detected from a sample of carbon-14 would change with time. Fig. 1.1 Use the graph to calculate the half life of carbon-14. Show your working on the graph. …………………… years [2] (b) When a carbon-14 atom (14 6 C) emits radiation it changes into a nitrogen atom (14 7 N). Using this information, suggest the type of radiation emitted by carbon-14. Explain your answer. … …[2] 0 1 2 3 4 5 6 7 8 9 0 5000 10000 15000 20000 counts per minute time/years For Examiner’s Use © UCLES 2004

3 0654/03/O/N/04 [Turn over 2 Popcorn is a popular food. It is made by heating grains of the maize plant. Fig. 2.1 shows a cross section through a typical maize grain. Fig. 2.1 When the grain is heated, water in the endosperm vaporises and turns to steam. As the temperature increases, the pressure of the steam increases, and the starch in the endosperm softens and becomes fluid (more like a liquid than a solid). When the pressure inside the grain is high enough, the steam and fluid starch break through the seed coat. Fig. 2.2 shows the popped maize grain. Fig. 2.2 (a) Starch and glucose are carbohydrates. Starch is made of polymer molecules which can be broken down into glucose molecules. (i) Name the three elements in all carbohydrates. …[1] (ii) Using starch and glucose as examples, explain briefly the meanings of the terms monomer and polymer. … … …[2] (iii) Proteins are another very important group of substances made of polymer molecules. Name the element found in all proteins but not in carbohydrates. …[1] seed coat endosperm For Examiner’s Use © UCLES 2004

4 0654/03/O/N/04 (b) Explain in terms of the motion of molecules why the steam pressure inside the maize grain increases when the temperature increases. … …[2] (c) The starch, which bursts through the seed coat when the maize grain pops, cools quickly to form a solid foam. Fig. 2.3 shows a magnified view of the inside of the solid foam. Fig. 2.3 (i) What general name is given to a mixture in which one substance is dispersed in another? …[1] (ii) An emulsion, such as milk, is an example of a mixture in which one substance is dispersed in another. Explain why it is not possible to see through emulsions like milk. Draw some light rays on the diagram in Fig. 2.4 to help you to answer this question. Fig. 2.4 … …[2] starch bubbles originally formed by steam and now filled with air For Examiner’s Use © UCLES 2004

5 0654/03/O/N/04 [Turn over (d) Popcorn is often made by heating the maize grains in a cooking pot made from an aluminium alloy. In the boxes below, draw labelled sketches to show how the atoms are arranged in a piece of pure aluminium and in a piece of an aluminium alloy. One aluminium atom has been drawn in each box. [4] For Examiner’s Use © UCLES 2004 O O pure aluminium aluminium alloy

6 0654/03/O/N/04 3 Fig. 3.1 is a photograph of part of a leaf, taken using a light microscope. Fig. 3.1 (a) The presence of chloroplasts shows that these are plant cells, and not animal cells. (i) On the photograph, label one feature, other than chloroplasts, which is present in plant cells but not in animal cells. [1] (ii) Describe the function of the feature you have labelled. … … …[2] (b) Explain how the structure of these cells enables photosynthesis to be carried out effectively. … … … … …[2] For Examiner’s Use © UCLES 2004 palisade layer spongy layer chloroplasts

7 0654/03/O/N/04 [Turn over (c) Explain how the position of these cells in the leaf enables them to obtain each of the following requirements for photosynthesis. (i) light … … …[2] (ii) carbon dioxide … … …[2] (d) What name is given to a group of similar cells such as the palisade layer in a leaf? …[1] For Examiner’s Use © UCLES 2004

8 0654/03/O/N/04 4 (a) Fig. 4.1 shows an athlete running a race. Fig. 4.1 Some forces acting on the athlete are • a support force, A, from the ground pushing on the athlete, • a friction force, B, from the ground helping the athlete to move, • the weight, C, of the athlete, • the force of air resistance, D, which slows the athlete. Draw arrows on Fig. 4.1 to show the direction of each of these forces. Label each force clearly using the letters B – D. The direction of force A has been drawn for you. [2] (b) Good sprinters are said to need strong leg muscles and small body mass. Explain why these characteristics may be useful to a sprinter as he accelerates from the starting blocks. … … … …[3] For Examiner’s Use © UCLES 2004

9 0654/03/O/N/04 [Turn over (c) A spectator is sitting 85 m from the starting gun. When the race is started, the spectator sees the athletes run off and a little later hears the bang from the starting gun. The spectator thinks that there was a false start, when the athletes started running before the starting gun was fired. The speed of sound is 340 m / s. Explain why the athletes did not have a false start. … … …[2] For Examiner’s Use © UCLES 2004

10 0654/03/O/N/04 5 A student investigated the reaction of four metals, P, Q, R and S, with dilute hydrochloric acid. Fig. 5.1 shows what the student observed during the experiment. Fig. 5.1 (a) Name the gas given off in these reactions. …[1] (b) The student thought that the results clearly showed the reactivity order of the metals. (i) List the metals in reactivity order suggested by the observations. ……………. (most reactive) ……………. ……………. ……………. (least reactive) [1] (ii) State three conditions that would need to be kept the same for each reaction if the observations are to be a reliable indication of the reactivity of the metals. 1 … 2 … 3 …[3] P Q R S For Examiner’s Use © UCLES 2004

11 0654/03/O/N/04 [Turn over (c) The student then investigated the electrolysis of seven aqueous solutions, using the apparatus shown in Fig. 5.2. Fig. 5.2 His results are shown in Table 5.1. Table 5.1 Part of the reactivity series is shown below. potassium (most reactive) magnesium (hydrogen) copper silver (least reactive) (i) Use the patterns in the results shown in Table 5.1 to predict the electrode products in the examples below. [2] power pack electrode A electrode B For Examiner’s Use © UCLES 2004 solution product at electrode A product at electrode B potassium sulphate hydrogen gas oxygen gas magnesium nitrate hydrogen gas oxygen gas copper sulphate copper metal oxygen gas silver nitrate silver metal oxygen gas potassium chloride hydrogen gas chlorine gas magnesium chloride hydrogen gas chlorine gas copper chloride copper metal chlorine gas solution product at electrode A product at electrode B copper nitrate magnesium sulphate

12 0654/03/O/N/04 (ii) Suggest a general rule for predicting the product at electrode A from the reactivity series. … … …[2] 6 Fig. 6.1 is a transverse section through a human eye. Fig. 6.1 (a) On the diagram, draw label lines to (i) the area where an image is focused, and label it F, [1] (ii) a part of the eye that prevents too much light from reaching the retina, and label it P. [1] (b) Describe how information from the eye is transmitted to the brain. … … …[2] ciliary muscle For Examiner’s Use © UCLES 2004

13 0654/03/O/N/04 [Turn over (c) Explain how the contraction of the ciliary muscle helps the eye to focus on a nearby object. … … … …[3] (d) The eyes of snakes contain only cones, with no rods. Use this information to make two statements about the vision of snakes. 1 … … 2 … …[2] (e) Many snakes hunt for prey, such as small mammals, at night. They have structures in their heads called pit organs, which can sense infra-red radiation. This helps them to locate their prey even when it is completely dark, because small mammals emit much more infra-red radiation than their surroundings. (i) State one way in which infra-red radiation differs from light. …[1] (ii) Suggest why mammals emit much more infra-red radiation than their surroundings. … … …[2] For Examiner’s Use © UCLES 2004

14 0654/03/O/N/04 7 Fig. 7.1 shows the motion of a bus from one stop to the next. Fig. 7.1 (a) Describe the motion of the bus during BC and during CD. BC … … CD … …[2] (b) Calculate the distance covered by the bus from A to D. Show your working. …………………………………[3] 0 100 200 300 400 0 5 10 15 20 speed/ m per s time/s A B C D For Examiner’s Use © UCLES 2004

15 0654/03/O/N/04 [Turn over (c) Fig. 7.2 shows two toy buses. Bus A has a mass of 0.5 kg and bus B has a mass of 0.3 kg. Both buses are moving in the same direction. Fig. 7.2 Bus A is travelling at 1.0 m / s and bus B is travelling at 0.5 m / s. When they collide, bus A and bus B join together and move in the same direction. Calculate the speed at which they continue to move. Show your working and state the formula that you use. formula used working …………………………………[3] 1.0m/s 0.5m/s A B © UCLES 2004 For Examiner’s Use

16 0654/03/O/N/04 (d) The headlamps on a bus are connected in parallel as shown in Fig. 7.3. Fig. 7.3 Each headlamp has a resistance of 4 ohms. Calculate the combined resistance of the two headlamps. Show your working and state the formula that you use. formula used working …………………………………[2] 12 V For Examiner’s Use © UCLES 2004

17 0654/03/O/N/04 [Turn over 8 The manufacture of ammonia and of sulphuric acid are two important industrial processes. Fig. 8.1 is a simplified diagram of the type of reaction vessel which is used in both processes. Fig. 8.1 (a) The manufacture of ammonia and of sulphuric acid both involve reversible, redox reactions which require a catalyst. (i) State the purpose of a catalyst. …[1] (ii) The reactant gases required to make ammonia are nitrogen and hydrogen. Explain why the exit gas stream contains all three of these gases. … … …[2] (iii) The equation below shows one of the reactions involved in the manufacture of sulphuric acid. The equation is not balanced. Balance the equation. SO2 + O2 SO3 [1] (iv) Name the substance that is oxidised in this reaction. …[1] catalyst exit gas stream reactant gases For Examiner’s Use © UCLES 2004

18 0654/03/O/N/04 (b) Draw a diagram of an ammonia molecule, NH3, showing how the outer electrons are arranged. [2] (c) Ammonia reacts with dilute nitric acid to make the salt ammonium nitrate. NH3 + HNO3 → NH4NO3 A student makes a solution of ammonium nitrate by mixing the solutions shown in Fig. 8.2. Fig. 8.2 (i) Show that the number of moles of ammonia and the number of moles of nitric acid that the student uses are both 0.01. …[3] 100cm3 of 0.1 mol/dm3 nitric acid 50cm3 of 0.2 mol/dm3 aqueous ammonia For Examiner’s Use © UCLES 2004

19 0654/03/O/N/04 [Turn over (ii) The student leaves the mixture to evaporate. Calculate the mass of ammonium nitrate crystals that she will obtain. (relative atomic masses N = 14; O = 16; H= 1.) …………………………………[3] For Examiner’s Use © UCLES 2004

20 0654/03/O/N/04 9 Hog deer (Fig. 9.1) are herbivores which live in regions of Pakistan and India. They feed on grass. Hog deer are killed and eaten by tigers. Fig. 9.1 (a) (i) Construct a food chain using the information above. [1] (ii) What do the arrows in your food chain represent? …[1] (iii) Sketch a pyramid of biomass representing this food chain. Label each part of the pyramid using the correct terms for the feeding levels. [3] For Examiner’s Use © UCLES 2004

21 0654/03/O/N/04 [Turn over (b) Hog deer are normally brown, but occasionally an albino (pure white) hog deer is born. (i) Suggest how this might occur. … … …[2] (ii) Explain how natural selection is likely to ensure that very few albinos are present in a population of hog deer. … … … … …[4] For Examiner’s Use © UCLES 2004

22 0654/03/O/N/04 10 (a) Microwaves travel at 300 000 000 m / s. Calculate the frequency of a microwave of wavelength 6 cm. Show your working and state the formula that you use. formula used working …………………………………[3] (b) A microwave oven was used to heat 0.5 kg of milk contained in a plastic cup. The temperature of the milk was 15 °C when it was placed in the microwave oven and 95 °C when it was taken out. The specific heating capacity for milk is 4500 J / kg °C. (i) Calculate the amount of energy transferred from the microwave oven to the milk. Show your working and state the formula that you use. formula used working …………………………………[3] © UCLES 2004 For Examiner’s Use

23 0654/03/O/N/04 To heat the milk, 240 000J of electrical energy was transferred to the microwave oven. (ii) Use your answer to part (i) to calculate the efficiency of the energy transfer. …………………………………[1] (iii) Suggest why the energy transfer is not 100% efficient. … …[1] (c) Fig. 10.1 shows a reed switch used as a safety device in a microwave oven. Fig. 10.1 Suggest what the reed switch contains and how this ensures that the microwave oven only operates when the oven door is shut. … … …[3] reed switch in microwave generator circuit magnet in edge of door © UCLES 2004 For Examiner’s Use University of Cambridge International Examinations is part of the University of Cambridge Local Examinations Syndicate (UCLES), which is itself a department of the University of Cambridge.

24 0654/03/O/N/04 © UCLES 2004 Group DATA SHEET The Periodic Table of the Elements 140 Ce Cerium 58 141 Pr Praseodymium 59 144 Nd Neodymium 60 Pm Promethium 61 150 Sm Samarium 62 152 Eu Europium 63 157 Gd Gadolinium 64 159 Tb Terbium 65 162 Dy Dysprosium 66 165 Ho Holmium 67 167 Er Erbium 68 169 Tm Thulium 69 173 Yb Ytterbium 70 175 Lu Lutetium 71 232 Th Thorium 90 Pa Protactinium 91 238 U Uranium 92 Np Neptunium 93 Pu Plutonium 94 Am Americium 95 Cm Curium 96 Bk Berkelium 97 Cf Californium 98 Es Einsteinium 99 Fm Fermium 100 Md Mendelevium 101 No Nobelium 102 Lr Lawrencium 103 1 H Hydrogen 1 7 Li Lithium 3 23 Na Sodium 11 24 Mg Magnesium 12 40 Ca Calcium 20 45 Sc Scandium 21 48 Ti Titanium 22 51 V Vanadium 23 52 Cr Chromium 24 55 Mn Manganese 25 56 Fe Iron 26 59 Co Cobalt 27 59 Ni Nickel 28 64 Cu Copper 29 65 Zn Zinc 30 70 Ga Gallium 31 27 Al Aluminium 13 11 B Boron 5 12 C Carbon 6 14 N Nitrogen 7 16 O Oxygen 8 19 F Fluorine 9 28 Si Silicon 14 31 P Phosphorus 15 32 S Sulphur 16 35.5 Cl Chlorine 17 40 Ar Argon 18 20 Ne Neon 10 4 He Helium 2 73 Ge Germanium 32 75 As Arsenic 33 79 Se Selenium 34 80 Br Bromine 35 84 Kr Krypton 36 39 K Potassium 19 88 Sr Strontium 38 89 Y Yttrium 39 91 Zr Zirconium 40 93 Nb Niobium 41 96 Mo Molybdenum 42 Tc Technetium 43 101 Ru Ruthenium 44 103 Rh Rhodium 45 106 Pd Palladium 46 108 Ag Silver 47 112 Cd Cadmium 48 115 In Indium 49 119 Sn Tin 50 122 Sb Antimony 51 128 Te Tellurium 52 127 I Iodine 53 131 Xe Xenon 54 137 Ba Barium 56 139 La Lanthanum 57 * 178 Hf Hafnium 72 181 Ta Tantalum 73 184 W Tungsten 74 186 Re Rhenium 75 190 Os Osmium 76 192 Ir Iridium 77 195 Pt Platinum 78 197 Au Gold 79 201 Hg Mercury 80 204 Tl Thallium 81 207 Pb Lead 82 209 Bi Bismuth 83 Po Polonium 84 At Astatine 85 Rn Radon 86 Fr Francium 87 227 Ac Actinium 89 † 9 Be Beryllium 4 I II III IV V VI VII 0 85 Rb Rubidium 37 133 Cs Caesium 55 226 Ra Radium 88 The volume of one mole of any gas is 24 dm3 at room temperature and pressure (r.t.p.). a X b a = relative atomic mass X = atomic symbol b = proton (atomic) number Key *58-71 Lanthanoid series †90-103 Actinoid series

UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS International General Certificate of Secondary Education MARK SCHEME for the November 2004 question paper 0654 CO-ORDINATED SCIENCES 0654/03 Paper 3 (Extended Theory), maximum mark 100 This mark scheme is published as an aid to teachers and students, to indicate the requirements of the examination. It shows the basis on which Examiners were initially instructed to award marks. It does not indicate the details of the discussions that took place at an Examiners’ meeting before marking began. Any substantial changes to the mark scheme that arose from these discussions will be recorded in the published Report on the Examination. All Examiners are instructed that alternative correct answers and unexpected approaches in candidates’ scripts must be given marks that fairly reflect the relevant knowledge and skills demonstrated. Mark schemes must be read in conjunction with the question papers and the Report on the Examination. CIE will not enter into discussion or correspondence in connection with these mark schemes. CIE is publishing the mark schemes for the November 2004 question papers for most IGCSE and GCE Advanced Level syllabuses. www.XtremePapers.com

Grade thresholds taken for Syllabus 0654 (Co-Ordinated Sciences) in the November 2004 examination. minimum mark required for grade: maximum mark available A C E F Component 3 100 65 41 20 13 The threshold (minimum mark) for B is set halfway between those for Grades A and C. The threshold (minimum mark) for D is set halfway between those for Grades C and E. The threshold (minimum mark) for G is set as many marks below the F threshold as the E threshold is above it. Grade A* does not exist at the level of an individual component.

November 2004 INTERNATIONAL GCSE MARK SCHEME MAXIMUM MARK: 100 SYLLABUS/COMPONENT: 0654/03 CO-ORDINATED SCIENCES Paper 3 (Extended Theory)

Page 4 Mark Scheme Syllabus Paper IGCSE – NOVEMBER 2004 0654 3 © University of Cambridge International Examinations 2005 1 (a) evidence of working; 5400 - 5500 years ‘ 2 (b) neutron converted to proton; therefore loses an electron; beta emission; 2 max Total 4 2 (a) (i) carbon, hydrogen and oxygen; 1 (ii) monomer is small molecule/idea of building block; links in a chain (to form a polymer); 2 (iii) nitrogen; 1 (b) molecules/particles, move faster/gain kinetic energy; collide with inside of seed coat, more frequently/with more force; 2 (c) (i) colloid; 1 (ii) transparency means light rays are passing through; (in emulsion) light rays are, scattered/reflected; light rays shown, reflected/scattered, on diagram; 2 max (d) (i) pure metal diagram shows all atoms same size; close packed with regular pattern; alloy diagram shows at least two different sizes of atoms; close packed but with one atom size breaking the regularity; 4 Total 13 3 (a) (i) label to cell wall or position of vacuole, plus appropriate name; 1 (ii) cell wall supports the cell/holds cell in shape; stops it bursting when it takes up water; prevents entry of fungi; vacuole contains cell sap; store of, minerals/sugars/(soluble) nutrients; reference to turgor; max 2 (b) chloroplasts; which contain chlorophyll; (chlorophyll) absorbs sunlight; max 2

Page 5 Mark Scheme Syllabus Paper IGCSE – NOVEMBER 2004 0654 3 © University of Cambridge International Examinations 2005 (c) (i) 1 near the (upper) surface of the leaf; 2 only, epidermis/one layer, above them; 3 epidermis cells have no chloroplasts so more light reaches palisade cells; 4 cells are arranged, upright/vertically; 5 so light does not have to pass through many cell walls; max 2 (ii) 1 air spaces/gaps; 2 in, spongy layer/cells just below palisade layer; 3 are in contact with outside air; 4 allow diffusion (of carbon dioxide); max 2 (d) tissue; 1 Total 10 4 (a) B arrow pointing right; C arrow pointing vertically downwards; D pointing left; 2 marks for all three correct, 1 mark for 1 correct 2 (b) force = mass x acceleration; so large force = large acceleration/small = small; small mass requires less force (to provide acceleration); 3 (c) light travels, virtually instantaneously/faster than sound; time taken for sound to reach spectator is longer than light; use of figures, e.g. 85 ÷ 340 = 0.25 s; max 2 Total 7 5 (a) hydrogen ‘ 1 (b) (i) Q, P. R, S; 1 (ii) same temperature; same acid concentration; same solid surface area; no insoluble salt formed; max 3 (c) (i) copper nitrate - A copper; B oxygen; magnesium sulphate - A hydrogen; B oxygen; any two for one mark max 2

Page 6 Mark Scheme Syllabus Paper IGCSE – NOVEMBER 2004 0654 3 © University of Cambridge International Examinations 2005 (ii) if metal (ion in electrolyte) is above hydrogen then hydrogen is produced; if below hydrogen then metal forms (on electrode surface ); note Allow one mark for the idea that more reactive metals give hydrogen and less reactive ones give the metal 2 Total 9 6 (a) (i) label line F to retina; 1 (ii) label line P to iris; 1 (b) as electrical signal/electrical impulse/action potential/nerve impulse; along a sensory, neurone nerve cell; in the optic nerve; max 2 (c) (contraction) reduces the diameter of the ciliary muscle; slackens tension on the suspensory ligaments; allows lens to become thicker; decreases focal length of the lens/bends light rays more strongly; max 3 (d) they can see colour; they cannot see (well) in the dark; 2 (e) (i) longer wavelength/lower frequency; 1 (ii) they are warmer (than their surroundings); they regulate their body temperature/they are homeothermic /endothermic; heat generated by, metabolic reactions/respiration/muscle activity; max 2 Total 12 7 (a) BC constant speed/20 ms-1; CD slowing (to a stop)/decelerating (to 0 ms-1); 2 (b) evidence of working; AB 1000 m, BC 4000 m, CD 500 m; total distance = 5500 m; 3 (c) momentum = mass x velocity or formula showing initial momentum = final momentum; working; v = 0.8125 ms-1; 3 (d) 1/R = 1/R1 + 1/ R2; accept alternative version R = 2 ohms; 2 Total 10

Page 7 Mark Scheme Syllabus Paper IGCSE – NOVEMBER 2004 0654 3 © University of Cambridge International Examinations 2005 8 (a) (i) speeds the reaction; 1 (ii) reaction is reversible; so some product reacts to form reactants; mixture passes too quickly through reaction chamber/some nitrogen and hydrogen do not react; max 2 (iii) 2SO2
O2 + 2SO2 ; 1 (iv) sulphur dioxide; 1 (b) three shared pairs; lone pair on nitrogen; 2 (c) (i) use of formula - moles = (vol in cm3 ÷ 1000 ) x concentration; (allow other correct working) for the acid (100 ÷ 1000) x 0.1 (= 0.01); for the ammonia (50 ÷ 1000) x 0.2 (= 0.01); 3 (ii) recognises that 0.01 moles of salt will be produced; calculates formula mass of salt = (14 x 2) + (1 x 4) + (16 x 3) = 80; 0.8 g 3 Total 13 9 (a) (i) grass
hog deer
tiger; 1 (ii) energy; 1 (iii) three rectangular boxes stacked centrally on each other; largest box at bottom and smallest at top; labelled producer + primary consumer + secondary consumer; 3 (b) (i) caused by, genes/alleles/DNA; mutation; in cell producing gametes; by both parents having a recessive allele for albino; albino offspring is homozygous for this allele; max 2 (ii) albino deer more likely to be killed/eaten/brown ones more likely to survive; by tigers/predators; because they are, less well adapted/too easily seen; less likely to (live long enough to) reproduce; so do not pass on their genes; max 4 Total 11 10 (a) frequency = velocity ÷ wavelength; wavelength = 0.06 m (or shown in calculation); frequency = 5 x 109 Hz; 3 (b) (i) energy = mass x shc x change in temperature; = 0.5 x 4500 x 80; = 180 000 J; 3

Page 8 Mark Scheme Syllabus Paper IGCSE – NOVEMBER 2004 0654 3 © University of Cambridge International Examinations 2005 (ii) 0.75/75 %; 1 (iii) some energy lost as, heat/light/sound; 1 (c) reed contains magnetic strip; magnet closes switch when door is closed; this completes circuit; 3 Total 11