L.35/36. Pre-Leaving Certificate Examination, Physics. Marking Scheme. Page 1 of 51

Transcription

1 L.35/36 Pre-Leaving Certificate Examination, 2017 Physics Marking Scheme Ordinary Pg. 4 Higher Pg. 29 Page 1 of 51

2 exams Pre-Leaving Certificate Examination, 2017 Physics Ordinary & Higher Levels Table of Contents Ordinary Level Section A Higher Level Section A Q Q Q Q Q Q Q Q Section B Section B Q Q Q Q Q Q Q Q Q Q Q Q Q Q Q Q L.35/36_MS 2/60 Page 2 of 59 exams

3 exams Pre-Leaving Certificate Examination, 2017 Physics Ordinary & Higher Levels Explanation Conventions Used 1. A dash before an answer indicates that the answer is a separate answer, which may be considered as independent of any other suggested answers to the question. 2. A forward slash / before an answer indicates that the answer is synonymous with that which preceded it. Answers separated by a forward slash cannot therefore be taken as different answers. 3. A double forward slash // is used to indicate where multiple answers are given but not all are required. 4. Round brackets ( ) indicate material which is not considered to be essential in order to gain full marks. 5. etc. is used in this marking scheme to indicate that other answers may be acceptable. In all other cases, only the answer given or words to that effect may be awarded marks. 6. In calculations, 3 marks are deducted for a mathematical error but no further penalty is incurred if the problem, otherwise correct, is completed. Allow for rounding unless specified otherwise; accept an answer given within a reasonable range if the method of calculation is correct. Current Marking Scheme Assumptions about these marking schemes on the basis of past SEC marking schemes should be avoided. While the underlying assessment principles remain the same, the exact details of the marking of a particular type of question may vary from a similar question asked by the SEC in previous years in accordance with the contribution of that question to the overall examination in the current year. In setting these marking schemes, we have strived to determine how best to ensure the fair and accurate assessment of students work and to ensure consistency in the standard of assessment from year to year. Therefore, aspects of the structure, detail and application of the marking schemes for these examinations are subject to change from past SEC marking schemes and from one year to the next without notice L.35/36_MS 3/60 Page 3 of 59 exams

4 exams Pre-Leaving Certificate Examination, 2017 Physics Ordinary Level Marking Scheme (400 marks) SECTION A (120 marks) Answer three questions from this section. Each question carries 40 marks. Section A Question 1 (40 marks) 1. In an experiment to verify Boyle s law for a fixed mass of gas, the volume of a gas, V, was measured for a number of different pressures, P. The table below shows the data recorded. P (kpa) V (cm 3 ) V (cm3 ) (i) Draw a labelled diagram of the arrangement of the apparatus used in this experiment. (12) ** Diagram to include: (4 3m) enclosed / trapped volume of gas method of measuring volume, e.g. scale method of measuring pressure, e.g. pressure gauge method of varying pressure ** Deduct (2m) if no labels included. (ii) State one other quantity, other than the fixed mass of gas, that was kept constant in this experiment. (4m) (4) temperature L.35/36_MS 4/60 Page 4 of 59 exams

5 2017 LC Physics [OL] Section A Question 1 (cont d.) (iii) Copy the table above and complete it in your answerbook. (6 1m) (6) ** Award 1m for each correct value of 1 V. P (kpa) V (cm 3 ) V (cm3 ) (iv) Using the data in the completed table, draw a graph on graph paper of P against 1 V. (4 3m) (12) ** Graph to include: axes labelled correctly, P against 1 V 4 points plotted correctly another 3 points plotted correctly straight line through the points and origin ** Deduct 3m if graph paper not used P (kpa) V (cm 3 ) (v) Explain how your graph verifies Boyle s law. (2 3m) (6) straight line through origin shows that P is proportional to 1 V L.35/36_MS 5/60 Page 5 of 59 exams

6 2017 LC Physics [OL] Section A Question 2 (40 marks) 2. During an experiment to measure the specific heat capacity of a substance (e.g. water or a metal), a student recorded a number of temperature and mass readings. The student used these measurements to calculate the specific heat capacity of the substance. (i) Draw a labelled diagram of the arrangement of the apparatus used in this experiment. (12) ** Diagram to include: (4 3m) liquid in calorimeter / block of metal method of heating (mixtures or electrical method) method of measuring energy provided to substance thermometer / insulation / other relevant detail ** Accept other appropriate answers. ** Deduct 2m if no labels included. (ii) What temperature measurements did the student take during the experiment? (2 3m) (6) temperature of substance before heating temperature of substance after heating / any other relevant temperature (iii) What mass measurements did the student take during the experiment? (6) Any 2: (2 3m) mass of substance / liquid / metal // mass of calorimeter // mass of calorimeter + liquid // etc. ** Accept any 2 measurements consistent with diagram. (iv) Write the formula that would have been used by the student to calculate the specific heat capacity of the substance. (10) E = m w c w (+m c c c ) consistent with diagram (10m) ** any reference to mc (6m) ** relevant attempt at word version of formula (3m) (v) Give an assumption that was made by the student when using this formula that could result in an error in the final value recorded. (6) Any 1: (6m) no loss in heat to surroundings // all other objects besides substance / liquid / calorimeter in experiment, e.g. thermometer, have negligible heat capacity // etc. ** Accept other appropriate answers L.35/36_MS 6/60 Page 6 of 59 exams

7 Section A Question 3 (40 marks) 3. An experiment was carried out to investigate the relationship between the fundamental frequency, f, of a stretched string and the length of the string, l. The length of a stretched string was measured when its fundamental frequency of vibration corresponded to the frequency of a vibrating source of sound. This was repeated for a number of different frequencies LC Physics [OL] (i) Draw a labelled diagram of the arrangement of the apparatus that may have been used to collect this data. (12) ** Diagram to include: (4 3m) tuning fork or some frequency source sonometer stretched string with two bridges or equivalent ** Deduct 2m if no labels included. (ii) State one quantity that is kept constant during this experiment. (6) Any 1: (6m) tension of string (same string) // mass of string (same string) (iii) How were the frequencies of the vibrating sources of sound changed during the experiment? (3m) (9) use different tuning forks / sound generator with variable frequency How were the corresponding lengths of the stretched strings determined? (2 3m) adjust length of stretched string (e.g. move bridge) until resonance is observed (e.g. piece of paper jumps off string) (iv) What is the relationship between frequency and length that would have been discovered in this experiment? (2 3m) (6) frequency is inversely proportional to / f length / 1 l (v) Draw a sketch of the graph that would verify this relationship. (7m) (7) sketch of frequency (f) against 1 l ** Axes correctly labelled. ** Straight line drawn through origin L.35/36_MS 7/60 Page 7 of 59 exams

8 2017 LC Physics [OL] Section A Question 4 (40 marks) 4. A student carried out a laboratory experiment to investigate how the resistance, R, of a thermistor varies with temperature,. The table below shows the data collected. ( C) R (Ω) (i) Draw a labelled diagram of the arrangement of apparatus used in this experiment. (12) ** Diagram to include: (4 3m) thermistor in water container method of measuring temperature method of measuring resistance connected to thermistor method of heating water ** Deduct 2m if no labels included. (ii) Name the instruments used to measure the resistance and temperature values. (6) Resistance (3m) ohmmeter (or equivalent) Temperature (3m) thermometer (or equivalent) (iii) Plot a graph, on graph paper, of the resistance against temperature,, for a thermistor. (12) ** Graph to include: (4 3m) axes labelled correctly at least 3 points plotted correctly another 3 points plotted correctly smooth curve drawn through the points ** Deduct 3m if graph paper not used L.35/36_MS 8/60 Page 8 of 59 exams

9 2017 LC Physics [OL] Section A Question 4 (cont d.) (iii) (cont d.) R (Ω) θ at 1600 Ω θ ( C) (iv) Use your graph to determine at what temperature the resistance of the thermistor is 1600 Ω. (6) line drawn across from 1600 Ω on graph (3m) temperature 34 C (3m) ** Accept any reasonable reading from the graph. ** Award full marks for any reading in range 33 C 35 C. (v) How does the resistance of the thermistor vary with temperature? (4m) (4) resistance decreases as temperature increases L.35/36_MS 9/60 Page 9 of 59 exams

10 2017 LC Physics [OL] SECTION B (280 marks) Answer five questions from this section. Each question carries 56 marks. Section B Question 5 (56 marks) 5. Answer any eight of the following parts (a), (b), (c), etc. ** Marks awarded for the eight best answers. (a) Give an example of (i) a vector quantity and (ii) a scalar quantity. (4m + 3m) (7) (i) (ii) vector quantity Any 1: force // acceleration // velocity // weight // momentum // etc. scalar quantity Any 1: time // speed // distance // mass // volume // length // energy // electric charge // etc. (b) Why is the acceleration due to gravity on the moon less than the acceleration due to gravity on the Earth? (7m) (7) the mass of the moon is much smaller than that of the Earth ** Award 3m for reference to different masses / moon smaller / Earth bigger. (c) What is the power developed by a person who lifts a weight of 60 N through a height of 5 m in 12 seconds? (4m + 3m) (7) work = 60 5 = 300 J power = = 25 W (d) What is meant by a thermometric property? (4m + 3m) (7) a property that changes measurably with temperature L.35/36_MS 10/60 Page 10 of 59 exams

11 2017 LC Physics [OL] Section B Question 5 (cont d.) (e) Why is the decibel adapted, db(a), scale used when constructing sound-level meters? (4m + 3m) (7) scale adapted to frequency response of the human ear (f) What is the power of a convex lens of focal length 10 cm? (4m + 3m) (7) power = 1 f = 10 m1 / 1 10 = 0.1 cm1 (g) State two uses for capacitors. (7) Any 2: (4m + 3m) tuning radios // flash guns // smoothing currents // filtering frequencies // etc. (h) How does a residual current device (RCD) act as a safety device in a circuit? (4m + 3m) (7) detects the difference between current in live and neutral wire switches off / trips the current if above a certain value (i) What is a photon? (4m + 3m) (7) a packet of energy associated with electromagnetic radiation (j) Choose from the list below the scientist who (i) named the electron, and (ii) measured the charge on the electron. (4m + 3m) (7) Bohr Stoney Millikan Chadwick (i) named the electron Stoney (ii) measured the charge on the electron Millikan L.35/36_MS 11/60 Page 11 of 59 exams

12 2017 LC Physics [OL] Section B Question 6 (56 marks) 6. Define momentum. (2 3m) (6) mass multiplied by velocity ** Award full marks for correct notation explained, P = mv. State the principle of conservation of momentum. (3 3m) (9) total momentum of a system before collision is equal to the total momentum of the system after collision if no external force acts on it Explain how the principle of conservation of momentum applies in launching a rocket ship. (8) momentum of gas fired out of back of rocket ship (3m) equal to momentum gained by rocket ship (3m) speed increases (2m) A white snooker ball of mass 0.18 kg travelling at 0.5 m s 1 strikes a stationary black snooker ball of mass 0.2 kg. After the collision the white snooker ball travels at 0.1 m s 1 in the same direction. The black ball travels in the same direction as the white ball after the collision. Calculate (21) (i) the momentum of the white ball before the collision (2 3m) P = mv = (0.18)(0.5) = 0.09 kg m s L.35/36_MS 12/60 Page 12 of 59 exams

13 2017 LC Physics [OL] Section B Question 6 (cont d.) (ii) the loss of momentum of the white ball during the collision (2 3m) After collision P = (0.18)(0.1) = kg m s 1 Loss of momentum = = kg m s 1 (iii) the speed of the black ball after the collision. (3 3m) momentum before = momentum after 0.09 = v v = 0.36 m s 1 After the collision the white ball travels a distance of 2 m before it stops, without striking any cushion. Calculate (12) (iv) the deceleration of the white ball after the collision (2 3m) v 2 = u 2 + 2as 0 2 = a(2) a = m s 1 (v) the time after the collision it takes the white ball to stop. (2 3m) v = u + at 0 = t 40 s L.35/36_MS 13/60 Page 13 of 59 exams

14 2017 LC Physics [OL] Section B Question 7 (56 marks) 7. In a periscope light is deflected twice through 90. Light can be deflected by reflection using mirrors or by total internal reflection using prisms. Mirror (i) Explain the underlined terms. Light ray (12) reflection (2 3m) light sending back / returning / bouncing from a mirror / off a (shiny) surface total internal reflection (2 3m) light going from a denser to a rarer medium at an angle of incidence greater than critical angle 45 angle Mirror Periscope Eye (ii) State the laws of reflection of light. (6m + 3m) (9) the angle of incidence is equal to the angle of reflection incident ray, reflected ray, normal all lie in the same plane ** Award (3m) for one partially correct law. (iii) What is the angle of incidence in the periscope shown for both mirrors? (4m) (4) 45 (iv) Give two properties of the image produced upon reflection from a plane mirror. (6) Any 2: (2 3m) virtual image // upright // laterally inverted // same size // same distance behind mirror as object // etc. (v) Give an application for (a) a concave mirror and (b) a convex mirror. (6) (a) a concave mirror Any 1: (3m) make-up / cosmetic / vanity mirror // shaving mirror // dentist s mirror // focusing beam // projectors // etc L.35/36_MS 14/60 Page 14 of 59 exams

15 2017 LC Physics [OL] Section B Question 7 (cont d.) (v) (cont d.) (b) a convex mirror Any 1: (3m) car mirror // widening range of view at e.g. concealed entrances // security mirrors in shops // etc. (vi) Draw a ray diagram showing a periscope using two prisms instead of two mirrors. (12) ** Diagram to show: (4 3m) two prisms replacing mirrors prisms aligned correctly rays showing total internal reflection through 90 Light ray 45 prism 45 prism Eye (vii) If the critical angle for the glass in the prism is 41, calculate the refractive index of the glass. (7) 1 n = = 1 n = (4m) sin c sin 41 = 1.52 (3m) L.35/36_MS 15/60 Page 15 of 59 exams

16 2017 LC Physics [OL] Section B Question 8 (56 marks) 8. Light waves are electromagnetic waves and sound waves are mechanical waves. Distinguish between electromagnetic waves and mechanical waves. (2 3m) (6) electromagnetic waves do not need a medium mechanical waves need a medium State two other differences between light waves and sound waves. (9) Any 2: (6m + 3m) light waves travel faster (than sound waves) light waves are transverse // sound waves are longitudinal Draw a waveform of a musical note and mark in the (i) wavelength and (ii) amplitude of the wave. (9) ** Diagram showing: (3 3m) correct shape of waveform wavelength correctly marked amplitude correctly marked Wavelength Amplitude If the (i) pitch and (ii) loudness of the musical note increase, how does the shape of the waveform change? (8) (i) (ii) pitch increases (4m) wavelength gets shorter / crests closer together loudness increases (4m) amplitude increases L.35/36_MS 16/60 Page 16 of 59 exams

17 2017 LC Physics [OL] Section B Question 8 (cont d.) A note of frequency 480 Hz is produced by a man playing a flute on the side of a street. What is the wavelength of the note? (3 3m) (9) c = f 340 = (480) = m A woman travelling in a car hears the flute while passing the man playing the flute. What difference does the woman observe between when (i) she is travelling towards the man and (ii) she is travelling away from him? (10) (i) when she is travelling towards the man (3m) observes higher frequency / pitch than produced by flute (ii) when she is travelling away from the man (3m) observes lower frequency / pitch than produced by flute What name is given to this change? (4m) Doppler effect Give an example of where this effect is observed with light waves. (5) Any 1: (5m) red shift in light from stars // blue shift in light from stars // etc. (speed of sound in air = 340 m s 1 ) L.35/36_MS 17/60 Page 17 of 59 exams

18 2017 LC Physics [OL] Section B Question 9 (56 marks) 9. Coulomb s law of force between electric charges is an example of an inverse square law. State Coulomb s law of force between electric charges and give an example of another inverse square law. (12) Coulomb s law (3 3m) force of attraction / repulsion is proportional to product of charges / Q 1 Q 2 1 and inversely proportional to square of the distance between them / 2 d ** Award full marks for correct notation explained. Another inverse square law (3m) Newton s law of gravitation Draw a labelled diagram of a gold leaf electroscope and explain how a positive charge could be placed on the electroscope by induction. (18) ** Diagram showing: (3 3m) cap connected to gold leaf metal case with window insulation between metal case and cap / leaf How charge placed on electroscope (3 3m) bring negatively-charged object near cap (positive charge at cap, negative charge at leaf) ground cap negative charge repelled to earth remove negatively-charged object positive charge distributed evenly between cap and leaf What would be observed if a negatively-charged object was brought near the electroscope? (3m) (9) leaf collapses Explain this observation. (2 3m) positive charge attracted from leaf and is neutralised What is meant by point discharge? (2 3m) (12) loss of charge through a point on an object L.35/36_MS 18/60 Page 18 of 59 exams

19 Section B Question 9 (cont d.) Copy the diagram below into your answer book and show how a negative charge is distributed on the metal conductor. ** Diagram showing: (2 3m) most of the charge concentrated at point remainder evenly distributed at surface of conductor 2017 LC Physics [OL] Explain how this conductor could be used as a lightning conductor to protect a building. (5m) (5) attached vertically at side of building, lightning passes through the conductor rather than through the building L.35/36_MS 19/60 Page 19 of 59 exams

20 2017 LC Physics [OL] Section B Question 10 (56 marks) 10. What is radioactivity? (2 3m) (6) spontaneous emission of radiation (particles or rays) from (unstable) nuclei Name the scientist who discovered radioactivity and after whom the unit of radioactive decay is named. (3m) (3) (Henri) Becquerel (i) What is the nature of the three forms of radiation: alpha ( )-particles, beta ( )-particles and gamma ( )-rays? (10) -particles (3m) helium nucleus / 2 protons and 2 neutrons -particles (3m) (high speed) electron -rays (2 2m) high energy electromagnetic radiation / photon (ii) Describe an experiment that compares the penetrating power of -, - and -radiation. (4 3m) (12) different sheet placed between radioactive source and radiation detector -particles stopped by sheet of paper -particles stopped by thin sheet of metal / plastic -rays stopped by lead / thick concrete Carbon-14 ( 14 6C ) is a radioactive isotope of carbon with a half-life of 5730 years. It decays by emitting a β-particle. (iii) How many protons and neutrons does a Carbon-14 atom contain? (2 3m) (6) 6 protons 8 neutrons (iv) How long does it take for a sample with 800 billion Carbon-14 nuclei to decay until 100 billion Carbon-14 nuclei remain? (2 3m) (6) 800 billion 400 billion 200 billion 100 billion (3 half lives) = years L.35/36_MS 20/60 Page 20 of 59 exams

21 2017 LC Physics [OL] Section B Question 10 (cont d.) (v) Using page 79 of the Formulae and Tables booklet, determine what element is formed after a β-particle is emitted from Carbon-14 ( 14 6C ). (2 3m) (6) -decay increase in atomic number of 1 nitrogen / N (vi) Give two uses for radioactive substances. (7) Any 2: (4m + 3m) medical imaging // medical therapy // irradiation of food // used in agriculture // carbon dating // smoke detectors // atomic clocks // industrial - as an energy source // industrial - as a static eliminator // etc L.35/36_MS 21/60 Page 21 of 59 exams

22 2017 LC Physics [OL] Section B Question 11 (56 marks) 11. Read this passage and answer the questions below. (a) What are integrated circuits? (4m + 3m) (7) a large number of electronic components, e.g. transistors, diodes, etc. all on one small silicon chip (b) Why was the invention of the integrated circuit important in the development of electronics? (4m + 3m) (7) no longer needed to build separate components and join very large number of components in one integrated circuit (c) A transistor consists of different types of semiconductor material. What is a semiconductor? (4m + 3m) (7) a material of resistance / with a resistivity between that of a conductor and that of an insulator L.35/36_MS 22/60 Page 22 of 59 exams

23 2017 LC Physics [OL] Section B Question 11 (cont d.) (d) Within a transistor are layers of p-type and n-type semiconductors. Give one difference between p-type and n-type semiconductors. (7) Any 1: (7m) p-type majority charge carriers are positive holes / doped with boron n-type majority charge carriers are electrons / doped with phosphorus (e) Explain how p-type and n-type semiconductors are used in a semiconductor diode. (4m + 3m) (7) p-type and n-type are joined together to form a p-n junction (f) Draw a circuit diagram showing a semiconductor diode in forward bias. (7) ** Diagram showing: (4m + 3m) battery connected to correct symbol for diode / p-n junction correct direction of diode (g) A semiconductor diode is used in rectification of a.c. electricity. What is rectification? (4m + 3m) (7) conversion of a.c. to d.c. electricity (h) Name a material, other than silicon, used in the manufacture of semiconductors. (7) Any 1: (7m) germanium // cadmium sulfide // zinc sulfide // gallium arsenide // etc. ** Accept other appropriate examples L.35/36_MS 23/60 Page 23 of 59 exams

24 2017 LC Physics [OL] Section B Question 12 (2 28 marks) 12. Answer any two of the following parts (a), (b), (c), (d). (a) State one of the conditions that is necessary for a body to be in equilibrium. (6) Any 1: (2 3m) sum of forces in any direction equals zero sum of clockwise moments equals sum of anti-clockwise moments (about any point) or A uniform plank, of length 2 m and mass 5 kg, is placed on two supports as shown in the diagram. The plank is in equilibrium. F 20 cm 50 cm (i) Calculate the weight of the plank. (2 3m) (6) weight = mg = (5)(9.8) = 49 N (ii) Find the clockwise moment of the weight about the 20 cm mark on the plank. (8) clockwise moment (weight of plank) = mg d (3m) perpendicular distance = = 0.8 m (2m) = (49)(0.8) = 39.2 N m (3m) (iii) The clockwise moment of the weight about the 20 cm mark equals the anti-clockwise moment of the force F about the 20 cm mark. Calculate the value of the force F. (8) anticlockwise moment = F 1.3 (3m) 1.3F = 39.2 (3m) F = 30.2 N (2m) (acceleration due to gravity = 9.8 m s 2 ) L.35/36_MS 24/60 Page 24 of 59 exams

25 2017 LC Physics [OL] Section B Question 12 (cont d.) (b) Dispersion of light can be observed in a rainbow. What is meant by dispersion of light? (2 3m) (6) separation of light into its individual colours / wavelengths Explain, using a diagram, how you would demonstrate the dispersion of light using a prism. In your diagram, indicate which ray is the red light and which is the violet light. (10) beam of white light striking face of prism (3m) beam of light refracted at different angles at the first surface (2m) and at the second surface (2m) red light refracted least and violet light refracted most (3m) White light Red Prism Violet Name a piece of laboratory equipment that can disperse light by a method other than refraction. (3m) (6) diffraction grating / Young s slits Which colour is dispersed the most using this piece of laboratory equipment? (3m) red Name the type of electromagnetic radiation that has a wavelength (i) just below visible light and (ii) just above visible light in the electromagnetic spectrum. (6) (i) (ii) just below visible light (3m) ultra-violet just above visible light (3m) infra-red L.35/36_MS 25/60 Page 25 of 59 exams

26 2017 LC Physics [OL] Section B Question 12 (cont d.) (c) Explain the term electromagnetic induction. (2 3m) (6) a change in the magnetic field induces an electromagnetic force (emf) to produce a current A transformer is based on electromagnetic induction. P R I M A R Y Input Coil Output Coil S E C O N D A R Y What is the difference between a step-up transformer and a step-down transformer? (8) Step-up (4m) voltage in secondary > voltage in primary number of turns in secondary > number of turns in primary Step-down (4m) voltage in secondary < voltage in primary // number of turns in secondary < number of turns in primary There are 200 turns in the primary coil of a transformer and 45 turns in the secondary coil. Calculate the output voltage when 230 V a.c. is connected across the primary coil. (8) V V s p = N N s p (2m) Vs 45 = (3m) V s = V (3m) If all the energy is transferred in the transformer, and there is a resistance of 10 Ω in the secondary coil, what is the current flowing in the secondary coil? (2 3m) (6) V = IR = I(10) I = A L.35/36_MS 26/60 Page 26 of 59 exams

27 2017 LC Physics [OL] Section B Question 12 (cont d.) (d) What is nuclear fission? (2 3m) (6) the splitting of one large nucleus into two smaller nuclei How is energy produced in a nuclear fission reaction? (3 3m) (9) mass of products / particles after reaction less than mass of reactants / particles before reaction energy = (loss in mass) c 2 / E = mc 2 Give one example of an element that could be used as fuel in a nuclear fission reactor. (6) Any 1: (6m) uranium // plutonium // thorium What is the function of (i) control rods and (ii) the moderator in a nuclear fission reactor? (4m + 3m) (7) (i) (ii) function of the control rods to control the speed of the reaction / prevent neutrons travelling between the rods function of the moderator Any 1: slows down neutrons // prevents capture of neutrons L.35/36_MS 27/60 Page 27 of 59 exams

28 Notes: L.35/36_MS 28/60 Page 28 of 59 exams

29 exams Pre-Leaving Certificate Examination, 2017 Physics Higher Level Marking Scheme (400 marks) Answer three questions from this section. Each question carries 40 marks. SECTION A (120 marks) Section A Question 1 (40 marks) 1. A student investigated the relationship between the period and length of a simple pendulum by measuring the time taken, t, for 40 oscillations of a pendulum of length l. This procedure was repeated for a number of different lengths of the pendulum. The following data were recorded. l (cm) t (s) Draw a suitable graph, using the data above, to illustrate the relationship between the period and the length of a simple pendulum. (4 3m) (25) l (m) T (s) T 2 (s) T and T 2 calculated axes showing T 2 against l (or l against T 2 ) points correctly plotted straight line through points and origin L.35/36_MS 29/60 Page 29 of 59 exams

30 2017 LC Physics [HL] Section A Question 1 (cont d.) T 2 (s 2 ) l (m) Use your graph to calculate a value for g, the acceleration due to gravity. take two points on the line (3m) use slope formula to measure slope, e.g. (0.37, 1.50), (0.85, 3.45) 1.95 =4.06 (allow a range of , if T 2 against l) 0.48 (4m) slope =, g =, e.g. g = g slope 4.06 (3m) g = 9.72 (3m) ** Allow answers in the range of 9.6 to 10.0 m s 2. ** Accept any reasonable reading from the graph. Apart from recording the time for 40 oscillations, state three precautions taken by the student to ensure that an accurate value for the acceleration due to gravity was obtained. (9) Any 3: (3 3m) small angle of oscillation (< 5 ) // length of pendulum should not be too short // oscillating in one plane only // length measured from point of suspension to centre of bob // small heavy bob to minimise air friction // fixed point of suspension // use a split cork to suspend pendulum // etc L.35/36_MS 30/60 Page 30 of 59 exams

31 2017 LC Physics [HL] Section A Question 1 (cont d.) The student measured another time for 40 oscillations as 45.4 s. However, the student forgot to record the length of the pendulum for this measurement. (6) Use your graph to estimate the length of the pendulum for this measurement. (2 3m) T = = T2 = 1.29 from graph read l as 0.31 m ** Allow answers in the range of 0.30 to 0.34 m. ** Accept any reasonable reading from the graph (0.85, 3.45) 3.00 T 2 (s 2 ) (0.37, 1.50) Estimated length) l (m) L.35/36_MS 31/60 Page 31 of 59 exams

32 2017 LC Physics [HL] Section A Question 2 (40 marks) 2. In an experiment to measure the focal length of a converging lens, the following values of the image distance, v, were measured for a number of different object distances u. Before taking these readings, an approximate value for the focal length was measured to be 30 cm. u (cm) v (cm) How could an approximate value of the focal length of the converging lens have been measured? (2 3m) (9) focus distant object onto a screen measure distance from lens to screen as approximate focal length What was the benefit of measuring an approximate value for the focal length before recording the above values? (3m) can place object outside focal point to ensure real image Describe, with the aid of a labelled diagram, how the image distance was measured. (12) Diagram showing: (6m) object correct lens screen / search pin ** Award (3m) for any two correct items. Description (2 3m) adjust position of screen until sharp image is obtained / adjust search pin position until no parallax measure distance from screen / search pin to centre of the lens Use all of the above data to calculate a more accurate value for the focal length of the converging lens. (15) Formula method = u v f (3m) Any 3 correct: (3 3m) = f, f = cm =, f = cm f = f, f = cm =, f = cm f Average f = 31.1 cm (3m) L.35/36_MS 32/60 Page 32 of 59 exams

33 2017 LC Physics [HL] Section A Question 2 (cont d.) Graph method (5 3m) calculate each 1 u and 1 v plot 1 u against 1 with correctly labelled axes v straight line with good distribution read off intercept values from graph 1 calculate f as ~ 31.1 cm (intercept value) u (cm) u v (cm) v Why would an object distance of 32 cm not have been chosen during this experiment? (4) Any 1: (4m) image formed very far from lens (more than 11 m) // image very large (not sharp) L.35/36_MS 33/60 Page 33 of 59 exams

34 2017 LC Physics [HL] Section A Question 3 (40 marks) 3. A student performed an experiment to measure the speed of sound in air by adjusting the length of a column of air, until it resonated with a tuning fork of known frequency f. The length, l, of the column of air was measured when it was vibrating at its first harmonic. The student also measured the diameter of the air column. The following data were recorded. f (Hz) l (cm) Diameter of the column of air = 3.5 cm Draw a labelled diagram of the apparatus used in the experiment and explain how the length of the column of air was adjusted. (12) Diagram showing: (3 3m) tuning fork held over column of air column of air (e.g. resonance tube) means of adjusting length of column (e.g. resonance tube in graduated cylinder of water) / metre stick, callipers Explanation (3m) describe method for adjusting length of column, e.g. resonance tube moved up and down in water How did the student know that the column of air was vibrating at its first harmonic? (2 3m) (6) the column of air initially very short length (e.g. resonance tube almost fully immersed in water) adjust length of air column (e.g. by lifting the tube out of the water) until loud sound is observed for the first time when tuning fork is struck Use all the data in the table to calculate the speed of sound in air. (12) C = 4f (l + 0.3d) (3m) = 4(512)[ (0.035)] = m s 1 (3m) Both correct: (3m) = 4(427)[ (0.035)] = m s 1 = 4(341)[ (0.035)] = m s 1 average value = m s 1 (3m) For the 512 Hz tuning fork, the student continued to increase the length of the column of air until resonance was observed for a second time and continued adjusting the length to the position where resonance was observed for a third time. Calculate the distance between these two positions. (10) distance between the position where resonance was observed for the second time and for the third time = ½ (3m) l + 0.3d = ¼ (2m) l + 0.3d = (0.035) = m (2m) distance between 2nd and 3rd time = 2(0.1635) = m (3m) L.35/36_MS 34/60 Page 34 of 59 exams

35 2017 LC Physics [HL] Section A Question 4 (40 marks) 4. In an experiment to verify Joule s law, a coil of resistance 10 Ω was placed in 250 g of water in an insulated cup. A current, I, was passed through the coil for a set time and the rise in temperature,, was recorded. This was repeated for a number of different currents. The current was passed through the coil for the same length of time for each setting of the current. The following data were recorded. I (A) ( C) Draw a labelled diagram of the arrangement of the apparatus used in this experiment. (10) Diagram showing: power supply connected to coil in water (3m) method of varying current (2m) ammeter and thermometer (3m) correct arrangement (2m) Using the recorded data, draw a suitable graph to verify Joule s law. (18) Explain how the graph verifies Joule s law. Graph (4 3m) calculate 6 values of I 2 labelled axes, against I 2 (or I 2 against ) 6 points correctly plotted straight line with good fit I 2 (A 2 ) How verifies Joule s law (2 3m) Joule s law is I 2 / power current 2 verified by straight line through the origin Δθ (ºC) I 2 (A 2 ) L.35/36_MS 35/60 Page 35 of 59 exams

36 2017 LC Physics [HL] Section A Question 4 (cont d.) Assuming all the electrical energy in the coil is absorbed by the water, use your graph to calculate the time the current flowed for each value of the current. (12) two points chosen from line / and I 2 taken from point on line (2m) 2 2 I slope ( 2 ) or ( I ) calculated correctly / ( I 2 ) or ( I ) calculated 13.5 between 2.5 and 2.7 (for 2 ), e.g. I 5.2 = 2.6 (3m) = mc t 2 I R (3m) (0.25)(4180)2.6 formula filled in correctly; e.g. t = = 272 s 10 (2m) t between 260 and 280 s (2m) (10, 25.5 ) 20 Δθ (ºC) (4.8, 12 ) I 2 (A 2 ) (specific heat capacity of water = 4180 J kg 1 K 1 ) L.35/36_MS 36/60 Page 36 of 59 exams

37 2017 LC Physics [HL] Answer five questions from this section. Each question carries 56 marks. SECTION B (280 marks) Section B Question 5 (56 marks) 5. Answer any eight of the following parts, (a), (b), (c), etc. ** Marks awarded for the eight best answers. (a) State Newton s second law of motion. (4m + 3m) (7) force is proportional to rate of change of momentum ** Award full marks for correct notation explained, F = ma. (b) The acceleration due to gravity on the surface of the planet Jupiter is 26.7 m s 2. The mass of Jupiter is kg. What is the radius of Jupiter? (4m + 3m) (7) = GM 11 g 2 R ; 26.7 = ( )( R R = m 27 ) (c) At what speed would light travel in an optical fibre whose refractive index is 1.46? (4m + 3m) (7) n = c v v = c n v = = m s (d) Draw a diagram of a thermocouple in operation. (7) Diagram showing: (4m + 3m) iron wire and copper wire / any two wires of different metals with voltmeter joined at hot and cold junction L.35/36_MS 37/60 Page 37 of 59 exams

38 2017 LC Physics [HL] Section B Question 5 (cont d.) (e) Calculate the tension of a stretched string of mass 0.35 g and length 70 cm when it is vibrating with a fundamental frequency of 420 Hz. (7) = = (2m) 1 T f = 2 l, 1 T (0.7) 5 10 (3m) T = N (2m) (f) Copy the diagram of the solid metallic conductor shown into your answer book and indicate how a positive charge would be distributed on it. (4m + 3m) (7) all charge on outside of conductor correct distribution (more concentrated at pointed end) (g) Explain why the current flowing in circuit B is smaller than that flowing in circuit A. (4m + 3m) (7) 12 V 12 V Circuit A Circuit B 6 Ω 6 Ω only ohmic resistance opposing in circuit A ohmic and back electromotive force (emf) opposing current in circuit B induced emf in coil in circuit B reduces resultant voltage, hence less current or L.35/36_MS 38/60 Page 38 of 59 exams

39 2017 LC Physics [HL] Section B Question 5 (cont d.) (h) Give one use of X-rays in (i) medicine and (ii) industry. (4m + 3m) (7) (i) Use in medicine Any 1: X-ray photography of bone / tissue // destroying cancerous cells (ii) Use in industry Any 1: detecting structural flaws in pipework // measuring thickness of material without the need for cutting // photographing machines // luggage scanning machines at airports // etc. (i) If the half life of a radioactive isotope is 12 years, what fraction of the undecayed nuclei in a sample of the isotope will decay after 60 years? (7) 60 years is 5 half-lifes (2m) = remains undecayed after 60 years (3m) will decay (2m) 32 (j) Give the quark composition of an anti-neutron. To which family of particles does it belong? (7) udd baryons ** Correct composition (4m). ** Family (3m). or A galvanometer has an internal resistance of 6 Ω and a full-scale deflection of 10 ma. Calculate the value of the resistor that must be placed in series with the galvanometer to produce a voltmeter of full-scale deflection 10 V. (4m + 3m) (7) R(0.01) + 6(0.01) = 10 R = 994 Ω L.35/36_MS 39/60 Page 39 of 59 exams

40 2017 LC Physics [HL] Section B Question 6 (56 marks) 6. What is meant by centripetal force? (3m) (15) force towards the centre that keeps object travelling in a circle Explain how the centripetal force changes if (i) the angular velocity is doubled, while the radius remains constant (2 3m) F = mω 2 r F ω 2 force multiplies by 4 (ii) the radius is doubled, while the linear velocity remains constant. (2 3m) F = mv F 1 r r force halves 2 The Indianapolis Speedway track consists of four straights (two of length 1000 m and two of length 200m) and four curved sections (each a quarter of the circumference of a circle of length 400m) as shown. The curved sections are banked (sloped inwards) at an angle of approximately 10 towards the centre of the track, while the straights have no banking, i.e. they are flat m Inside 10º Outside Curved section 400 m 200 m In the first lap of a race, a car accelerates from rest at an average rate of 5 m s 2, until a speed of 346 km h 1 is reached. The car continues at this speed for the remainder of the first lap. Calculate (19) (i) the distance travelled to reach the maximum speed 346 km h 1 = = 96.1 m s 1 (3m) v = u + at 96.1 = 0 + 5t (3m) t = s (2m) s = ut + ½at 2 = (0)(19.22) + ½(5)(19.22) 2 = m (3m) v 2 = u 2 + 2as = s) 9235 = 10s s = m or (ii) the time taken for the car to complete the first lap. length of 1 lap = (2 1000) + (4 400) + (2 200) = 4000 m remaining distance at constant speed = = m (3m) time = distance = = 32.0 s speed 96.1 (3m) total time = = 51.2 s (2m) L.35/36_MS 40/60 Page 40 of 59 exams

41 2017 LC Physics [HL] Section B Question 6 (cont d.) The fastest time recorded for one lap of the Indianapolis Speedway track is s and was achieved in a car of mass 700 kg. Assuming the car travels at constant speed during this lap, calculate the angular velocity of the car as it travels on the curved sections of the track. (10) 400 = ¼(2 r) (3m) r = m (2m) 4000 v = = m s1 (2m) v = = = rad s 1 r (3m) What is the maximum force exerted on the car as it travels around the curved section of the track? (5) F = mω r = (700)(0.4145) 2 mv (700)( ) ( ) / F = = r (3m) = N (2m) Why is banking of the track at curved sections beneficial to racing drivers? (7) it enables greater force towards the centre (3m) so they travel at faster speed (2m) without toppling over (2m) L.35/36_MS 41/60 Page 41 of 59 exams

42 2017 LC Physics [HL] Section B Question 7 (56 marks) 7. Interference is observed when waves from two coherent sources meet. Explain the underlined terms. (9) interference (3m) when two waves meet, new wave produced / waves add displacement coherent sources (2 3m) same frequency in phase / constant phase difference Explain, using a diagram, how an interference pattern is formed from two coherent sources. (12) Diagram showing: (4 3m) semi-circular wavefronts from two sources overlapping positions of constructive interference highlighted (e.g. crest meeting crest) positions of destructive interference highlighted (e.g. crest meeting trough) A helium-neon (HeNe) laser of wavelength 632 nm has a power rating of 35 mw. The HeNe laser is normally incident on a diffraction grating with 300 lines per mm. An interference pattern is formed on a wall parallel to and 2 m from the grating. Calculate the distance between the third order images on either side of the central image. (13) 1 d = 300 mm = m (3m) n = dsin 9 (3)( ) sin = (3m) = (2m) tan = 2 x, x = m (3m) distance between third order fringes = = 2.77 m (2m) Laser Grating 2 m Wall L.35/36_MS 42/60 Page 42 of 59 exams

43 2017 LC Physics [HL] Section B Question 7 (cont d.) Calculate (10) (i) the energy of one photon from the HeNe laser beam E = hc (3m) 34 8 ( )(3 10 ) E = J (3m) 9 ( ) (ii) the number of photons emitted per second from the laser J per second (2m) = photons (2m) 19 ( ) The laser beam is then pointed at a block of copper in the shape of a cube of side 2 cm for 5 minutes. Assuming that 90% of the light is absorbed by the copper and no heat is lost to the surroundings, calculate the rise in temperature of the block of copper. (12) energy absorbed by copper = 0.9( ) = 9.45 J (3m) mass of copper = V = ( ) = g (3m) Δ θ = E mc (3m) 9.45 = = 0.34 C ( )(390) (3m) (density of copper = 8.92 g cm 3 ; specific heat capacity of copper = 390 J kg 1 K 1 ) L.35/36_MS 43/60 Page 43 of 59 exams

44 2017 LC Physics [HL] Section B Question 8 (56 marks) 8. Variable capacitors used in radio frequency circuits usually consist of an array of parallel plates, with half of the plates being static and the other half able to be moved. Define capacitance. (2 3m) (6) ratio of charge to potential ** Accept Q C = with explanation of terms for (6m). V Describe an experiment that demonstrates how the capacitance of a parallel plate capacitor depends on the overlap area of its plates. (4 3m) (15) plates charged and aligned opposite each other one plate connected to gold leaf electroscope, causing leaf to diverge move one plate so that overlap area decreases observe increase in divergence of leaf indicates that potential increases capacitance decreases as area decreases ** Allow other appropriate experiments, e.g. multimeter with a capacitance setting. The capacitance of a parallel plate capacitor also depends on distance between plates. Name the other factor on which the capacitance of a parallel plate capacitor depends. (3m) dielectric / material between plates Explain why bringing a negatively charged conductor near a positively charged conductor increases the capacitance of the positively charged conductor. (7) bringing negatively charged conductor near positively charged conductor reduces potential of positively charged conductor / easier to move 1 C charge towards positively charged conductor (3m) as C = Q V, (2m) C increases (2m) L.35/36_MS 44/60 Page 44 of 59 exams

45 2017 LC Physics [HL] Section B Question 8 (cont d.) A power supply of potential difference 1200 V is connected 20 cm across two identical parallel plates d cm apart in air. The areas of the two plates completely overlap and the dimensions are shown in the diagram. If a charge of 0.6 µc is stored on both plates, calculate d 30 cm (18) (i) the energy stored on the capacitor 50 cm C = Q V = ( ) (3m) = F (2m) W = ½CV 2 = ½( )(1200) 2 (3m) = J (2m) (ii) the distance d between the plates. εa d= C (3m) 12 ( )( ) d (3m) = m (0.266 cm) (2m) The top plate is then moved 20 cm to the right as shown above and the distance d is multiplied by 1.5. What potential difference would need to be applied to keep the energy stored on the capacitor constant? (10) 12 C A ( )( ) = d (3m) F (2m) = ½( )V 2 (3m) V (2m) L.35/36_MS 45/60 Page 45 of 59 exams

46 2017 LC Physics [HL] Section B Question 9 (56 marks) 9. The electric motor is a device that converts electrical energy to mechanical energy. In 1820 Andre-Marie Ampere proposed the theoretical principle behind how an electric motor works. In 1821 Michael Faraday demonstrated this principle in an experiment. State the principle on which an electric motor works. (2 3m) (12) force on a current-carrying conductor in a magnetic field Name two other devices based on the same principle. Any 2: (2 3m) loudspeaker // galvanometer // ammeter // voltmeter // etc. ** Accept other appropriate answers. The definition of the unit of electric current, the ampere, is based on the principle on which a motor works. Define the ampere. (16) two infinitely long wires of negligible cross sectional area (2m) 1 m apart in a vacuum (2m) experience a force of N per unit length (3m) Describe an experiment that demonstrates this principle. (3 3m) conductor free to move (e.g. strip of tin foil) connected to power supply between two poles of a magnet / cut by a magnetic field when current switched on, conductor deflects An electric motor has a coil of dimensions 4 cm 6 cm with 50 turns in the coil. The coil is in the horizontal plane and is cut by a horizontal magnetic field of flux density 15 T, at right angles to the 6 cm side of the coil. The coil rotates around an axis parallel to the 6 cm sides of the coil and through the middle of the 4 cm sides. When a current flows through the coil, the coil experiences a maximum torque of 1.4 N m. 4 cm 6 cm Axis B = 15 T Calculate (23) (i) the force acting on one 6 cm side of the coil (2 3m) torque = F d F = = 35 N L.35/36_MS 46/60 Page 46 of 59 exams

47 2017 LC Physics [HL] Section B Question 9 (cont d.) (ii) the current flowing through the coil F = NBIL (3m) 35 = (50)(15)I(0.06) (3m) I = A (2m) (iii) the force on the 4 cm side of the coil when the angle of the coil from the horizontal is 45. F = NBILsin (3m) F = (50)(15)(0.778)(0.04)sin 45 (3m) F = 16.5 N (3m) Explain why the torque changes as the coil rotates while the size of the force on each 6 cm side remains constant. (3m + 2m) (5) force is constant because 6 cm side always perpendicular to magnetic field moment changes because perpendicular distance changes L.35/36_MS 47/60 Page 47 of 59 exams

48 2017 LC Physics [HL] Section B Question 10 (56 marks) 10. Answer either part (a) or part (b). (a) An experiment performed at Cambridge University in 1932 by English scientist John Cockroft and an Irish scientist resulted in the first experimental verification of Einstein s E = mc 2. It also involved the first artificial splitting of a nucleus. Name the Irish scientist, who became the only Irish person to receive a Nobel Prize in Physics in (3m) (3) Ernest Walton Describe, with the aid of a labelled diagram, the experiment performed by these two men. (4 3m) (12) hydrogen discharge tube producing protons accelerated by high voltage to strike lithium target producing alpha particles striking zinc sulfide / fluorescent screen measured kinetic energy of alpha particles ** Deduct (3m) if no diagram. In this experiment, what specifically do m and E stand for in E = mc 2? (2 3m) (20) m decrease / loss in mass due to the reaction E energy released / gain in kinetic energy of particles Calculate the values that would have been calculated for E and m in this experiment. mass of reactants (mass of proton + lithium nucleus) = = kg (3m) mass of reactants = kg mass of products (2 α-particles) = = kg (3m) m = loss in mass = kg (2m) E = mc 2 = ( )( ) 2 = J (3m) Explain how it was concluded that these results verified E = mc 2. (3m) measured increase in kinetic energy during experiment agreed with value calculated using E = mc L.35/36_MS 48/60 Page 48 of 59 exams

49 2017 LC Physics [HL] Section B Question 10 (cont d.) (a) (cont d.) In the Cambridge experiment in 1932, particles were accelerated to approximately 1 MeV. After 1932, scientists started to develop particle accelerators that accelerated charged particles to higher and higher energies, in the hope of producing and observing new particles in these accelerators. The Large Hadron Collider (LHC) at CERN is capable of accelerating particles to ev. In one collision of two protons in the LHC 64 Higgs bosons (each of mass kg) were produced. + leptons were also detected after the collision. What is the maximum number of + leptons that could have been produced during the collision? (21) maximum possible kinetic energy lost by protons in one collision = = J (3m) energy needed to produce 64 Higgs bosons = 64 ( )( ) 2 = J (2m) remaining energy = J (2m) energy needed to produce 1 τ + lepton = ( )( ) 2 = J (3m) 9 ( ) 10 ( ) = 16.3 (2m) maximum numbers of τ leptons = 16 (can only have even number as τ + and τ must both be produced) (3m) number of τ + leptons = 8 (2m) Why is it unlikely that 64 Higgs bosons would be produced in all other collisions between two protons in the LHC? (4m) in most collisions, not all the kinetic energy will be lost by protons (mass of a lithium nucleus = kg) L.35/36_MS 49/60 Page 49 of 59 exams

50 2017 LC Physics [HL] Section B Question 10 (cont d.) (b) What are logic gates? (2 3m) (9) an electronic circuit whose output voltage depends on input voltage in a defined way Name the Irish mathematician who devised the rules on which logic gates are based. (3m) George Boole Construct a truth table for (i) an AND gate and (ii) an OR gate. (20) Award (8 1m) for each correct pair of input values and output value. AND gate OR gate In 1 In 2 Out In 1 In 2 Out Describe how one of these truth tables could have been established experimentally. (4 3m) diagram showing option to apply inputs to gate as 0 V or to approximately 6 V (representing 1 in truth table) method of measuring / indicating output, e.g. voltmeter / LED each combination of inputs used, output measured / observed AND gate - both inputs need to be switched on to turn the output on OR gate - if at least one switch is on the output is on Draw a circuit diagram containing a bipolar transistor that will behave as a NOT gate. (24) Diagram showing: (5 3m) transistor with three inputs resistor (R CB ) connected correctly from collector to battery protective resistor at base V in shown between base and emitter V out shown between collector and emitter Clearly explain how the circuit behaves as a NOT gate. (3 3m) when V in is large, base current flows V out ~ 0, as collector-emitter resistance small compared to R CB when V in is zero, collector-emitter resistance is large compared to R CB and V out is large L.35/36_MS 50/60 Page 50 of 59 exams

51 2017 LC Physics [HL] Section B Question 10 (cont d.) (b) (cont d.) Give one other application for bipolar transistors. (3) Any 1: (3m) amplifier // switch // etc L.35/36_MS 51/60 Page 51 of 59 exams

52 2017 LC Physics [HL] Section B Question 11 (56 marks) 11. Read the following passage and answer the accompanying questions. (a) What is radioactivity? (4m + 3m) (7) spontaneous decay of unstable nuclei with the emission of radiation (b) It was later discovered that iron was not present in the sun. What two elements were later discovered to be present within the sun? (4m + 3m) (7) hydrogen helium (c) Write a nuclear equation for a fusion reaction that takes place in the sun. (2m + 1m + 2m + 2m) (7) H H 3 He + 1 n or 2 H + 3 H 4 He + 1 n ** Award a max. 3m if no numbers given. (d) Why are very large temperatures required for nuclear fusion to take place? (7) very large force needed to (3m) overcome force of repulsion between nuclei (4m) L.35/36_MS 52/60 Page 52 of 59 exams

53 2017 LC Physics [HL] Section B Question 11 (cont d.) (e) How are the lines observed in a spectrum recorded from a spectroscope explained by Bohr s model of the atom? (4m + 3m) (7) difference in energy between orbits when electrons move between levels equal to energy of photon (corresponding to line) emitted (f) State two differences between continuous spectra and line spectra. (7) ** Expect one point of information on each type of spectrum. Any 2: (4m + 3m) Continuous spectra produced by incandescent solid or liquid // all wavelengths are emitted // not characteristic of material that produced spectrum Line spectra produced by gas // only produces particular wavelengths // each element has different line spectrum (g) The sun emits joules of energy in a year. Calculate the change in mass of the sun in a year. (7) E = mc 2 (2m) = m( ) 2 (3m) = kg (2m) (h) Why will the rate at which energy is produced by the sun be considerably less in a few billion years? (7) there will be much fewer hydrogen atoms present / hydrogen atoms being used up in fusion reactions (4m) much fewer fusion reactions taking place (3m) L.35/36_MS 53/60 Page 53 of 59 exams

54 2017 LC Physics [HL] Section B Question 12 (2 28 marks) 12. Answer any two of the following parts (a), (b), (c), (d). (a) State the law of flotation. (2 3m) (6) weight of floating body is equal to weight of fluid displaced Using the law of flotation, explain why two objects A and B, identical in dimensions (10 cm 6 cm 6 cm) but with different densities, will float at different heights on the surface of water. (7) lower density object has lower weight / higher density object has more weight (2m) will displace less water / will displace more water (law of flotation) (2m) less of the object under water (floats higher) / more of the object under water (floats lower) (3m) d A 10 cm 10 cm B d Calculate the upward force exerted on the objects above in terms of d, the height of the floating objects above the surface. (9) pressure on bottom = gh = (1000)(9.8)(0.1 d) (3m) = d (3m) force = PA = ( d)( ) = d (3m) If one of the objects is pushed downwards and then released, explain why the object will initially travel upwards. (2 3m) (6) more of object under water more water displaced greater upthrust upthrust greater than weight of object net force upwards (density of water = 1000 kg m 3 ; acceleration due to gravity = 9.8 m s 2 ) L.35/36_MS 54/60 Page 54 of 59 exams

55 2017 LC Physics [HL] Section B Question 12 (cont d.) (b) Define specific latent heat. (2 3m) (6) the heat needed to change the state of 1 kg of a substance without a change in temperature In a nuclear fission reactor, liquid sodium is used as the circulating coolant and it transfers heat to water in the heat exchanger. The temperature of the liquid sodium entering the heat exchanger is 240 C and its temperature leaving the heat exchanger is 115 C. 10 L of water per second at 20 C enters the heat exchanger and is converted to steam at 100 C. Liquid sodium Control rods Steam Pressure vessel Graphite moderator Fuel rod Radiation shielding Heat exchanger Water circulator Water Cool gas duct Gas circulator Assuming no heat is lost to the surroundings, calculate (18) (i) the amount of heat energy per second required to produce steam in the heat exchanger Q = mc( ) + ml v (3m) = (10)(4180)(80) + (10)( ) (3m) = J (2m) (ii) the volume of liquid sodium that enters the heat exchanger every second. m s c s ( ) = J (3m) m s ( )( ) = (2m) m s = kg (2m) = m s V = = m 3 (3m) What is the purpose of the moderator in the reactor? (4m) (4) to slow down neutrons (specific heat capacity of water = 4180 J kg 1 K 1 ; specific latent heat of vaporisation of water = J kg 1 ; specific heat capacity of liquid sodium = J kg 1 K 1 ; density of liquid sodium = 927 kg m 3, 1 L of water has a mass of 1 kg) L.35/36_MS 55/60 Page 55 of 59 exams

56 2017 LC Physics [HL] Section B Question 12 (cont d.) (c) Define sound intensity. (2 3m) (6) the rate at which sound energy passes through unit area (at right angles to its path) ** Award full marks for correct notation explained, = P I A. A man sees a fire engine in the distance and hears the siren from a fire engine being turned on. The sound intensity detected by the man at that moment is W m 2. The man sees the fire engine travelling directly towards him and after a few seconds detects a sound intensity level increase of 12 db. At that time he can see that the fire engine is 100 m from his position. Assuming that sound energy is emitted at a constant rate and uniformly in all directions, what is (22) (i) the sound intensity observed by the man when the fire engine is 100 m from him (2 3m) 12 db sound intensity multiplies by 2, 4 times, stated or implied = W m 2 (ii) the rate at which sound energy is being emitted by the fire engine siren P I = 4 2 R, P = I(4 R 2 ) (3m) = ( )[4 (100) 2 ] (3m) = W (2m) (iii) the distance travelled by the fire engine from when the siren was switched on until it was 100 m from the man? 2 P R = 4 I (2 10 ) (3m) R = 400 m (3m) distance travelled = = 300m (2m) L.35/36_MS 56/60 Page 56 of 59 exams