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M13/4/PHYSI/SPM/ENG/TZ1/XX Physics Standard level Paper 1 Monday 6 May 2013 (morning) 45 minutes.

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1 M13/4/PHYSI/SPM/ENG/TZ1/XX Physics Standard level Paper 1 Monday 6 May 2013 (morning) 45 minutes

2 2. An archer aims five arrows at the centre of a target. The arrows strike the target as shown below. Which of the following describes the aim of the archer? A. Accurate and precise B. Accurate but not precise C. Precise but not accurate D. Neither accurate nor precise C C M13/TZ1

3 3. The graph below shows how velocity v varies with time t for a ball thrown vertically upwards from the Earth’s surface. The shaded area is equal to the A. displacement. B. final velocity. C. change in velocity. D. acceleration. 4. Two identical balls are dropped from a tall building, one a few seconds after the other. Air resistance is not negligible. As the balls fall, the distance between the balls will A. decrease. B. increase. C. increase then remain constant. D. remain constant. A C No air resistance y = 5 t 2 when a = 0 y = v t v is terminal speed timedistance 1 s5 m 2 s20 m 3 s45 m 4 s80 m M13/TZ1

4 5. Which of the following is always true for an object moving in a straight line at constant speed? A. No forces act on the object. B. No resultant force acts on the object. C. The momentum of the object is zero. D. No work is being done on the object. 6. A person of weight 600 N is standing on a weighing scale in a lift (elevator). The lift is accelerating upwards at 1.0 m s –2. Which of the following is the reading on the scale? A. 0 N B. 540 N C. 600 N D. 660 N B F net = ma F n – 600 = 60 F n = 660 N D M13/TZ1

5 7. A spaceship is moving at constant speed in outer space. An internal explosion causes it to break into two pieces that move in opposite directions. Which of the following best describes what happens to its total momentum and total kinetic energy as a result of the explosion? Total momentumTotal kinetic energy A.unchanged B.unchangedincreased C.increasedunchanged D.increased Momentum is conserved as the system is isolated. Kinetic energy obviously increases as the result of internal explosion. B M13/TZ1

6 8. A horizontal disc is rotating about a vertical axis through its centre. Points P and Q on the disc are at distances R and 2R respectively from the centre. The acceleration at P is a. Which of the following is the acceleration at Q? A. 0.5a B. a C. 2a D. 4a C kg of water at 100 °C is mixed with 1.0 kg of water at 0 °C in a container insulated from the surroundings. Which of the following is the final temperature of the water? A. 20 °C B. 25 °C C. 75 °C D. 80 °C D m 1 c 1 (100 – T) = m 2 c 2 (T – 0) c 1 = c (100 – T) = 1.0 T ⟹ 400 – 4 T = T Thermal energy given by hot water = thermal energy received by cold water M13/TZ1

7 10. Which of the following best describes the evaporation of a liquid? Location of processTemperature at which process can occur surfaceat any temperature of liquid surfaceat maximum liquid temperature only C.throughout liquidat any temperature of liquid D.throughout liquidat maximum liquid temperature only A 11. Which of the following is the temperature of an object related to? A. The kinetic energy of the object B. The random kinetic energy of the particles in the object C. The potential energy of the particles in the object D. The sum of the random kinetic energy and potential energy of the particles in the object B M13/TZ1

8 12. The acceleration of an object executing simple harmonic motion is proportional to the A. displacement of the object from equilibrium. B. velocity of the object. C. amplitude of oscillation. D. frequency of oscillation. A 13. A system, consisting of a mass M connected to a spring, oscillates on a frictionless surface with simple harmonic motion between two points, X and Y. Point O is the centre of the oscillation. For the system, at which of the following points is the elastic potential energy equal to the kinetic energy? A. O only B. X and Y only C. O, X and Y D. Neither O, X nor Y D v = ± ω (x 0 2 – x 2 ) 1/2 → Simple Harmonic Motion is periodic motion in which the acceleration/ restoring force is proportional to and in opposite direction of the displacement. M13/TZ1

9 14. Microwave ovens cause the water molecules in food to resonate. Water molecules have a natural frequency of vibration f. In order to heat the food most effectively, the frequency of the microwaves should have a value A. less than f. B. equal to f. C. greater than f. D. as large as possible. B Natural frequency is the frequency an object will vibrate with after an external disturbance. resonance: The increase in amplitude of oscillation of a system exposed to a periodic driving force with a frequency equal to the natural frequency of the system. If the frequency of a driving force matches the natural frequency of the system, this leads to a better absorption of energy by the system, resulting in large amplitude oscillations. M13/TZ1

10 15. Gas particles are equally spaced along a straight line. A sound wave passes through the gas. The positions of the gas particles at one instant are shown below. Which of the distances shown is equal to the wavelength of the wave? B Wavelength λ: the distance, measured in the direction of propagation of a wave, between two successive points with the same phase of oscillation. 16. A particle with positive charge +q moves freely from one plate held at potential V 1 to another plate held at potential V 2. Which of the following is the electric potential energy lost by the charge? A. qV 1 B. qV 2 C. q (V 1 +V 2 ) D. q (V 1 – V 2 ) D M13/TZ1

11 17. Which of the following graphs shows the relationship between current I and voltage V for a filament lamp? D Filament does not obey Ohm’s law because ratio voltage to current is not constant. We say tungsten is “non-ohmic” It’s resistance increases as current through it increases, because temperature increases. M13/TZ1

12 18. A cell of negligible internal resistance is connected to three identical lamps. A voltmeter is connected across one of the lamps. If the filament in lamp X breaks, the reading on the voltmeter will A. become zero. B. decrease. C. stay the same. D. increase. B V = IR R doesn’t change Current in the circuit flowing through resistor will be smaller if X breaks, because resistance of the parallel connection will increase, so will total resistance of the circuit, what results in smaller current. M13/TZ1

13 A M13/TZ1

14 20. Two point charges of size +2q and –q are placed as shown below. In which of the regions I, II and III can the resultant electric field strength be zero? A. I only B. II only C. III only D. I and III only C In region I electric field due to (+2q) is to the left and electric field due to (–q) is to the right, but one due to (+2q) is always greater then the other one. In region II both electric fields are to the right In region III electric field due to (+2q) is to the right and electric field due to (–q) is to the left, and there is the point at which the are equal in magnitude but in opposite direction resulting in zero resultant electric field. M13/TZ1

15 . 21. A wire is placed in a magnetic field which is directed to the right. The wire carries a current directed into the page. Which of the following is the direction of the force on the wire? D R-H-R 1: The direction of the magnetic force on a charge/current is given by the right-hand rule 1 Outstretch fingers in the direction of v (or current I). Curl fingers as if rotating vector v (I ) into vector B. Magnetic force on a positive charge (or I) is in the direction of the thumb Magnetic force on a negative charge points in opposite direction. M13/TZ1

16 22. Which of the following would decrease the initial activity of a sample of plutonium? A. Placing the sample in a lead container B. Placing the sample in a dark room C. Decreasing the mass of the sample D. Decreasing the temperature of the sample C M13/TZ1

17 23. A radioactive sample of initial activity 12 Bq has a half-life of 3 days. What is the activity after 6 days? A. 2 Bq B. 3 Bq C. 4 Bq D. 6 Bq B After 3 days activity is half of the initial one = 6 Bq After next 3 days activity is half of that one = 3 Bq 24. The reaction is an example of A. alpha decay. B. artificial transmutation. C. nuclear fusion. D. proton decay. B M13/TZ1

18 25. The diagram below shows an energy flow diagram (Sankey diagram) for a car. What is the efficiency of the car? A. 30 % B. 40 % C. 70 % D. 100 % A M13/TZ1

19 26. A small biofuel power station burns ethanol with an overall efficiency of 25 %. The energy density of ethanol is 30 MJ kg –1. The mass of fuel consumed every second is 50 kg. Which of the following gives the useful power output in MW? A M13/TZ1

20 27. An oscillating water column ocean-wave energy converter produces power P from waves of a certain amplitude and wavespeed. Which of the following would be the power produced from waves of twice the amplitude and twice the wavespeed? A. 2P B. 4P C. 8P D. 16P C Wave power: P/L amplitude of the wave A, length of wavefront L,  - density of waterM13/TZ1

21 28. The total power radiated by the Sun is P. The distance from the Sun to the Earth is d. The albedo of the Earth is α. What is the power absorbed by each square metre of the Earth’s surface? D M13/TZ1

22 29. Carbon dioxide is a greenhouse gas because A. it absorbs infrared light radiated by the Sun. B. it absorbs ultraviolet light radiated by the Earth. C. its natural frequency molecular oscillation lies in the infrared region. D. its natural frequency molecular oscillation lies in the ultraviolet region. C Short wavelength radiation is received from the sun and causes the surface of the Earth to warm up. The Earth will emit infra-red radiation (longer wavelengths than the radiation coming from the sun because the Earth is cooler than the sun). Some of this infra-red radiation is absorbed by gases in the atmosphere and re-radiated in all directions. Temperature of the Earth’s surface will be constant if the rate at which it radiates energy equals the rate at which it absorbs energy. The greenhouse effect is the warming of a planet due its atmosphere allowing in ultraviolet radiation from the Sun, but trapping the infrared radiation emitted by the warm Earth. The greenhouse gas has natural frequency of molecular oscillations in the infrared region, so they easily absorb energy in that region. When the frequency of the electric field is near to the natural frequency of an oscillation of the molecule, the amplitude will be high: The molecule absorbed energy from the field. Infrared radiation drives the vibration of the atoms; visible and UV radiation excites the electron cloud. The greenhouse gases like CO 2 or several organic gases have natural vibration frequency in the infrared domain. They absorb it very strongly. On the other hand, they are transparent for visible and UV light. So the visible and UV light arrives to the surface of the Earth, and is absorbed by metals, rocks, soil, and the leaves of the vegetation and also by waters. The molecules can re-radiate the absorbed energy, but it is more probable, that they collide with other molecules and excite vibrations. These vibrations emit infrared photons which can not go through the atmosphere, as the greenhouse gases absorb them. M13/TZ1

23 30. Which of the following is most likely to increase the rate of global warming? A. Deforestation B. Increasing the use of nuclear power stations C. Increasing the use of renewable energy sources D. Using natural gas instead of coal for electricity generation A M13/TZ1

24 M13/4/PHYSI/SPM/ENG/TZ2/XX Physics Standard level Paper 1 Monday 6 May 2013 (afternoon) 45 minutes

25 1.The length of the side of a cube is 10.0 ±0.3 cm. What is the uncertainty in the volume of the cube? A. ±0.027 cm 3 B. ±2.7 cm 3 C. ±9.0 cm 3 D. ±90 cm 3 D 2. Which of the following lists three vector quantities? A. momentum, electric field strength, displacement B. momentum, displacement, pressure C. pressure, electric current, displacement D. electric current, electric field strength, impulse A electric field strength is not a magnitude It is the whole vector M13/TZ2

26 3. An object, initially at rest, travels a distance d in a time t at a constant acceleration. What is the time taken for the object to travel 16d from rest at the same acceleration? A. 16t B. 8t C. 4t D. 2t C 4. An object is released above the surface of Earth. Which of the following correctly describes the speed and acceleration before it reaches terminal speed? Speed Acceleration A. increases remains constant B. increases decreases C. remains constant remains constant D. remains constant decreases B Air resistance provides a drag force to objects in free fall. ▪ The drag force increases as the speed of the falling object increases resulting in decreasing downward acceleration ▪ Although acceleration decreases, the speed still increases ▪ When the drag force reaches the magnitude of the gravitational force, the falling object will stop accelerating and fall at a constant velocity. This is called the terminal velocity/speed. M13/TZ2

27 5. An object of mass m is connected via a frictionless pulley to an object of mass M, where M > m. M rests on a horizontal frictionless surface. What is the acceleration of the system? A T = Ma mg - T = ma mg - Ma = ma a(M+m)=mg M13/TZ2

28 6. The graph shows the variation with distance x of the magnitude of the net force F acting on a body initially at rest. Which of the following describes how the kinetic energy and the acceleration of the body change with distance? Kinetic energy Acceleration A. decrease decrease B. decrease increase C. increase decrease D. increase increase C 1. ∆ KE = W net work done on an object will result in the change of kinetic energy (work is the area under the graph F vs. x) 2. As net F decreases, so does acceleration M13/TZ2

29 7. A ball of mass 0.40 kg travels horizontally and strikes a vertical wall with a speed of 5.0 m s –1. It rebounds horizontally with a speed of 3.0 m s –1. The ball is in contact with the wall for a time of 0.20 s. What is the average magnitude of the force exerted by the ball on the wall? A N B N C. 4 N D. 16 N D F ∆t = ∆ p = p final – p initial = m(v final – v initial ) ▪ we can choose coordinate system (vectors !!!) positive left or positive right ▪ as the force is positive we want final direction to be positive, so we choose left to be positive ▪ Then F (0.2) = 0.40 [3.0 – (–5.0)] = 3.2 ▪ F = 3.2/0.2 = 16 N (positive means to the left) M13/TZ2

30 8.A car on a road follows a horizontal circular path at constant speed. Which of the following correctly identifies the origin and the direction of the net force on the car? Origin Direction A. car engine toward centre of circle B. car engine away from centre of circle C. friction between car tyres and road away from centre of circle D. friction between car tyres and road toward centre of circle D Whatever the object, if it moves in a circle, there is some force acting upon it to cause it to deviate from its straight-line path, accelerate inwards and move along a circular path. Newton’s first law of motion – the law of inertia... objects in motion tend to stay in motion with the same speed and the same direction unless acted upon by a net force. For object's moving in circular motion, there is a net force acting towards the center which causes the object to seek the center. M13/TZ2

31 9. The temperature of an object is −153°C. Its temperature is raised to 273°C. What is the temperature change of the object? A. 699 K B. 426 K C. 153 K D. 120 K B M13/TZ2

32 10. Two ideal gases X and Y are at the same temperature. The mass of the molecules of gas X is twice the mass of the molecules of gas Y. Microscopic level: (absolute) temperature directly proportional to the average kinetic energy of the molecules of a substance: k is Boltzmann constant B M13/TZ2

33 B Avogadro’s number: Number of constituent particles (atoms/molecules) per mole of a given substance is 6.022×10 23 mol −1 M13/TZ2

34 12. Which graph shows how velocity v varies with displacement x of a system moving with simple harmonic motion? A Dependence on t: v = –  x 0 sin ωt = – v 0 sin ωt Be aware: M13/TZ2

35 D M13/TZ2

36 14. Light of wavelength 600 nm travels from air to glass at normal incidence. The refractive index of the glass is 1.5. The speed of light in air is c. Which of the following correctly identifies the speed of the waves and their wavelength in the glass? D M13/TZ2

37 15. Which of the following correctly describes the direction of a ray drawn relative to a wavefront for longitudinal and transverse waves? Longitudinal wave Transverse wave A. parallel parallel B. parallel perpendicular C. perpendicular parallel D. perpendicular perpendicular D M13/TZ2

38 C M13/TZ2

39 B M13/TZ2

40 18. A proton is accelerated from rest through a potential difference of 1000 V. What is the potential difference through which an alpha particle must be accelerated to gain the same kinetic energy as the accelerated proton? A V B V C. 500 V D. 250 V C 19. The magnitude of the gravitational field strength at the surface of a planet of mass M and radius R is g. What is the magnitude of the gravitational field strength at the surface of a planet of mass 2M and radius 2R? B M13/TZ2

41 20. Three positive point charges +Q are fixed in position at the vertices of an isosceles triangle. P is the mid point between two of the charges. Which arrow correctly identifies the direction of the electric field at point P? A. W B. X C. Y D. Z B The only electric field that survives at point P is the one due to charge at the right angle corner. The other two cancel each other out. M13/TZ2

42 21. Three wires, P, Q and R, carry equal currents directed into the plane of the paper. Which arrow correctly identifies the direction of the magnetic force on wire P? A. W B. X C. Y D. Z Currents in same direction attract! Currents in opposite direction repel! B M13/TZ2

43 22. Which particle is acted on by both the strong nuclear force and the Coulomb force? A. Antineutrino B. Electron C. Neutron D. Proton D 23. A nucleus of californium (Cf) contains 98 protons and 154 neutrons. Which of the following correctly identifies this nucleus of californium? C M13/TZ2

44 24. Which of the following gives the particles of the same energy in an increasing order of ionizing ability? A. β, α, γ B. α, β, γ C. γ, α, β D. γ, β, α D 25. The use of which energy source enhances the greenhouse effect the most? A. Wood B. Coal C. Wind D. Tidal B M13/TZ2

45 B M13/TZ2

46 27. Which of the following correctly describes the energy transformation within photovoltaic cells and within solar heating panels? Photovoltaic cells Solar heating panels A. solar to thermal solar to electrical B. solar to thermal solar to thermal C. solar to electrical solar to electrical D. solar to electrical solar to thermal D M13/TZ2

47 28. An oscillating water column (OWC) ocean-wave converter produces a power P. What is the power output of this converter if the amplitude and speed of the waves are both doubled? A. 2P B. 4P C. 8P D. 16P Wave power: P/L A - amplitude of the wave, L - length of wavefront  - density of water C M13/TZ2

48 29. The graph shows the spectrum of a black-body. Which graph shows the spectrum of a body of emissivity 0.5 at the same temperature as the black-body? (The original graph is shown dotted.) C M13/TZ2

49 30. A student states that the following factors may lead to global warming I. decreased albedo of the Earth’s surface II. increase in volcanic activity III. deforestation. Which of the above statements are correct? A. I and II only B. II and III only C. I and III only D. I, II and III D M13/TZ2

50 N13/4/PHYSI/SPM/ENG/NOV/XX Physics Standard level Paper 1 45 minutes Wednesday 6 November 2013 (morning)

51 1. The sides of a square are measured to be 5.0 ± 0.2 cm. Which of the following gives the area of the square and its uncertainty? A ± 0.2 cm 2 B ± 0.4 cm 2 C. 25 ± 2 cm 2 D. 25 ± 4 cm 2 C 2. Which of the following lists two vector quantities and one scalar quantity? A. force, mass, time B. acceleration, energy, momentum C. distance, impulse, power D. density, pressure, temperature BN13/NOV

52 3. A tennis ball is dropped from the top of a high building. Air resistance cannot be neglected. Which graph represents the variation with time t of the magnitude of the acceleration a of the ball before it hits the ground? BN13/NOV

53 Terminal speed – When air resistance is taken into account object in free fall will not accelerate forever. Air resistance depends on the speed of the object. As speed increases, so does air resistance until it reaches the value equal to the weight of the object. At that time net force is zero, so is acceleration. The speed doesn’t change any more. It is constant speed.N13/NOV

54 4. A model plane flies with constant velocity at constant height. Which diagram represents the forces acting on the plane? D Object is in translational equilibrium if velocity is const.N13/NOV

55 5. The net force on a body is F. The impulse of F is equal to the A. change in momentum of the body. B. rate of change of momentum of the body. C. change of kinetic energy of the body. D. change of total energy of the body. A Newton’s second law:: Impulse is defined as the product of the net force acting on an object and time interval of action: FΔt vector! (Ns) Impulse F∆t acting on an object will produce the change of its momentum Δp: F∆t = ∆p Δp = mv - mu Ns = kg m/sN13/NOV

56 6. In an inelastic collision A. momentum and kinetic energy are both conserved. B. momentum is conserved but kinetic energy is not. C. kinetic energy is conserved but momentum is not. D. neither momentum nor kinetic energy are conserved. BN13/NOV

57 7. A force which increases uniformly from 0 to a maximum value of F is applied to an object. The object does not move until the force exceeds 0.5F. As the force increases from 0.5F to F the object moves a distance x in the direction of the force. What is the work done by this force? A. 0.25Fx B. 0.5Fx C. 0.75Fx D. Fx C distance Work is the area under F vs distance graph force F 0.5 F xN13/NOV

58 8. A body moves with uniform speed around a circle of radius r. The period of the motion is T. What is the speed of the body? AN13/NOV

59 9. Molar mass is defined as A. the number of particles in one mole of a substance. B. 1/12 the mass of one atom of carbon-12. C. the mass of one mole of a substance. D. the number of particles in 1/12 of a mole of carbon-12. C 10. Which of the following is true about boiling and evaporation? Boiling Evaporation A. occurs throughout liquid occurs at liquid surface B. occurs throughout liquid occurs throughout liquid C. occurs at liquid surface occurs at liquid surface D. occurs at liquid surface occurs throughout liquid AN13/NOV

60 11. A solid of mass m is initially at temperature ΔT below its melting point. The solid has specific heat capacity c and specific latent heat of fusion L. How much thermal energy must be transferred to the solid in order to melt it completely? A. mL + mc B. mc + mLΔT C. mcΔT + LΔT D. mcΔT + mL D To bring solid to melting point Q = mc∆T is needed. And then Q = mL is needed to melt itN13/NOV

61 12. For a body undergoing simple harmonic motion the velocity and acceleration are A. always in the same direction. B. always in opposite directions. C. in the same direction for a quarter of the period. D. in the same direction for half the period. DN13/NOV

62 13. Which graph of displacement x against time t represents the motion of a critically damped body? A Critical/heavy damping: occurs if the resistive force is so big that the system returns to its equilibrium position without passing through it. The mass comes to rest at its equilibrium position without oscillating. The friction forces acting are such that they prevent oscillations.N13/NOV

63 14. Which of the following correctly relates the direction of oscillation of the particles in a medium to the direction of energy propagation for transverse and longitudinal waves? Transverse wave Longitudinal wave A. perpendicular perpendicular B. perpendicular parallel C. parallel perpendicular D. parallel parallel BN13/NOV

64 15. Which of the following relates the amplitude A of a travelling wave to the intensity I ? C 16. Two identical waves of wavelength λ leave two sources in phase. The waves meet and superpose after travelling different distances. Which path difference will result in destructive interference? B N13/NOV

65 17. A resistor X of resistance R is made of wire of length L and cross-sectional area A. Resistor Y is made of the same material but has a length 4L and a cross-sectional area 2A. X and Y are connected in series. What is the total resistance of the combination? A. 1.5R B. 2R C. 3R D. 9R C N13/NOV

66 18. A light dependent resistor L is connected in series with a cell C and a fixed resistor R. The cell has a negligible internal resistance. V OUT is the output voltage across L. Which change will increase V OUT ? A. Connect another resistor in parallel with L B. Decrease the intensity of light on L C. Increase the resistance of R D. Decrease the emf of C B A photoresistor or light-dependent resistor (LDR) or photocell is a light-controlled variable resistor. The resistance of a photoresistor decreases with increasing incident light intensity; in other words, it exhibits photoconductivity. A photoresistor can be applied in light-sensitive detector circuits, and light- and dark-activated switching circuits. If intensity of light decreases, R L increases, and V OUT increases N13/NOV

67 19. Each of the resistors in the circuit has a resistance of 2.0 Ω. The cell has an emf of 3.0 V and negligible internal resistance. The ammeter has negligible resistance. What is the ammeter reading? A. 0.4 A B. 0.5 A C. 1.5 A D. 2.0 A C 1/R TOT = 1/R + 1/3R = 4/3R R TOT = 3/2 Ω I = emf/R TOT = 2 A Current through one resistor I 1 Current through three resistors I 3 2 = I 1 + I 3 R I 1 = 3R I 3 I 1 = 3I 3 I 3 = 0.5 A I 1 = 1.5 AN13/NOV

68 20. Which diagram represents the pattern of electric field lines of two small positive point charges held at the positions shown? BN13/NOV

69 Both A and D will result in the product (abc) = N m 2, but the problem asks about gravitational force, not electric one. DN13/NOV

70 22. An electron of mass m e and charge e accelerates between two plates separated by a distance s in a vacuum. The potential difference between the plates is V. What is the acceleration of the electron? C N13/NOV

71 23. In a particular atom, the nucleon number is the total number of A. protons. B. neutrons. C. electrons. D. protons and neutrons. 24. For which quantity can the unit MeV c –2 be used? A. Mass B. Momentum C. Kinetic energy D. Binding energy D A Unit for mass is unit for energy (MeV) divided by c 2N13/NOV

72 25. Uranium-238 forms a nucleus of plutonium-239 as a result of A. electron capture followed by alpha decay. B. electron capture followed by beta decay. C. neutron capture followed by alpha decay. D. neutron capture followed by two beta decays. D 2 protons more means 2 neutrons into 2 protons and two electrons = two beta decays That would leave the same number of nucleons, so one extra neutron must be capturedN13/NOV

73 26. In the production of electric power, an advantage of using photovoltaic cells rather than fossil fuels is that the photovoltaic cells A. can be effective in any location. B. can be used continuously. C. have low initial set-up costs. D. are more environmentally friendly when in use. DN13/NOV

74 27. What is the main role of the control rods and the main role of the moderator in a thermal fission reactor? Control Rods Moderator A. decrease neutron speed decrease neutron speed B. decrease neutron speed absorb neutrons C. absorb neutrons decrease neutron speed D. absorb neutrons absorb neutrons C Main energy transformations in a nuclear power station: nuclear energy → thermal energy → mechanical energy → electrical energy Three important components in the design of all nuclear reactors are moderator, control rods and heat exchanger. ▪ Moderator is a medium that slows down fast neutrons to make them suitable for reaction (water, graphite, heavy water). ▪ Control rods are movable rods that readily absorb neutrons. They can be introduced or removed from reaction chamber in order to control the rate of fission of uranium and plutonium. Made of chemical elements capable of absorbing manyuraniumplutonium neutrons without fissioning themselves (cadmium, hafnium, boron, etc) ▪ Heat exchanger is used to seal off the place where nuclear reactions take place from the rest of the environment. In some nuclear power plants, the steam from the reactor goes through a heat exchanger to convert another loop of water to steam, which drives the turbine. The advantage to this design is that the radioactive water/steam never contacts the turbine.N13/NOV

75 28. An oscillating water column (OWC) ocean-wave energy converter uses waves to alter the air pressure in a chamber. Which energy resources must have been involved for this method to generate electricity? I. Tides II. Wind III. Solar A. I only B. II only C. I and II only D. II and III only D It is wave not tide !!!!N13/NOV

76 29. The surface temperature of a black-body emitter is doubled. By what factor does the power emitted by the body increase? A. 32 B. 16 C. 4 D. 2 B 30. Which option is not a possible solution to reduce the enhanced greenhouse effect? A. Decommission nuclear power plants B. Replace the use of coal and oil with natural gas C. Use combined heating and power systems (CHP) D. Use hybrid motor vehicles AN13/NOV

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