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Tung Wah Group of Hospitals Kap Yan Directors' College 2012-2013 MOCK EXAMINATION 19 Feb 2013 Total marks: 40 Name: _______________________ Class no.: ________ Class: _______ LPK Marks: __________ PHYSICS PAPER 2 Question-Answer Book Time allowed: 1 hour This paper must be answered in English INSTRUCTIONS (1) This paper consists of THREE sections, Sections A, B and C. Each section contains eight multiple-choice questions and one structured question which carries 10 marks. Attempt ALL questions in any TWO sections. (2) Write your answers in the spaces provided in this Question-Answer Book. Do not write in the margins. Answers written in the margins will not be marked. For multiple-choice questions, blacken the appropriate circle with an HB pencil. You should mark only ONE answer for each question. If you mark more than one answer, you will receive NO MARKS for that question. (3) Graph paper and supplementary answer sheets will be provided on request. Write your name and class number on each sheet and fasten them with string INSIDE this Question-Answer Book. (4) The diagrams in this paper are NOT necessarily drawn to scale. (5) The last two pages of this Question-Answer Book contain a list of data, formulae and relationships which you may find useful. (6) No extra time will be given to candidates for filling in the question number boxes after the ‘Time is up’ announcement. P.1 Answer ALL questions. Write your answers in the spaces provided. Section A: Astronomy and Space Science Q.1: Multiple Choice Questions 1.1 The photo of star trails above sea level was taken by an observer facing north at an unknown place P on Earth. The centre of the semicircles is close to the sea level. Which of the following statements is/are correct? (1) The latitude of place P is close to zero. (2) Stars can be seen rising nearly vertically when viewed from the eastern horizon. (3) The polaris is at the zenith. A. (1) only C. (1) and (2) only 1.2 Source and observer moving with the same velocity. Source moving along a circular path around an observer. Source moving away from a stationary observer. Source moving towards a stationary observer. X is twice as far away as Y. X is four times as far away as Y. Y is twice as far away as X. Y is four times as far away as X. Let T be the temperature of a black-body radiator, the frequency at which maximum radiation of energy occurs is proportional to A. T–4 1.5 C D A B C D B. T –1 C. T D. T4 A B C D A B C D Two satellites, S1 and S2, of the same mass revolve around the Earth in two different circular orbits. The ratio of the speeds of satellites S1 and S2 is 1: 2. Find the potential energy of satellite S2 if the potential energy of satellite S1 is E. Take the potential energy to be zero at infinity. A B C D A. 0.25E 1.6 B X and Y are identical stars with the same luminosity. When viewed from Earth, the brightness of star X is 4 times the brightness of star Y. Which of the following explanations is possible? A. B. C. D. 1.4 A In which of the following situations would a blue shift be observed? A. B. C. D. 1.3 B. (3) only D. (2) and (3) only B. 0.5E C. 2E D. 4E Which of the following statements must be correct? (1) If the luminosity of star A is higher than that of star B, the absolute magnitude of star A is lower than that of star B. (2) If the difference of apparent magnitude of two stars is 6, the brightness of one star is about 100 times the brightness of the other star. (3) If the surface temperature of star A is higher than that of star B, the absolute magnitude of star A is lower than that of star B. A. (1) only B. (3) only C. (1) and (2) only P.2 D. (2) and (3) only A B C D 1.7 The Moon orbits the Earth in an elliptic orbit as shown in the figure. It moves at a speed of 1076 m s–1 at point P. What is its speed at point Q? The mass of the Earth is 5.98 × 1024 kg. The forces acting on the Moon by the Sun and other planets can be ignored. A. 968 m s–1 B. 1037 m s–1 C. 1106 m s–1 A B C D D. 1174 m s–1 1.8 A star is moving towards the Earth at the speed of 40 km s1. What should be the change in position of the observed Hα line (λ0 = 656.1 nm) in the spectrum of this star? A. Red-shifted by 0.088 nm B. Red-shifted by 11.5 nm A B C D C. Blue-shifted by 0.088 nm D. Blue-shifted by 11.5 nm Q.1: Structured question A comet is a small celestial body orbiting the Sun. When it comes close to the Sun, it is heated up and its evaporated dust and gas form long tails (Figure 1.1). Halley is one of the best known comets. It orbits the Sun with a period of 75.3 years. Take the mass of the Sun to be 1.99 1030 kg. Figure 1.1 (a) Suppose Halley is 1.3 AU from the Earth at point P. An observer on the Earth can see a visible tail of Halley that is 9 long and perpendicular to the line of sight. Estimate the length of the tail in kilometres. (2 marks) ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ (b) Can we measure the distance between Halley and the Earth using the method of parallax? Explain briefly. (2 marks) ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ P.3 (c) Find the semimajor axis of Halley’s orbit in AU. The forces acting on Halley by planets in the solar system can be ignored. (2 marks) ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ (d) At perihelion (the point where an object is nearest to the Sun), the comet comes very close to the Sun’s surface. The perihelion distance is 8.75 x 1010 m. What is the farthest distance of the comet from the Sun? (1 mark) ____________________________________________________________________________________________ ____________________________________________________________________________________________ (e) Compare the speeds of Halley when it is at points Q and R. (1 mark) ____________________________________________________________________________________________ ____________________________________________________________________________________________ (f) Calculate the escape speed of Halley’s comet at the perihelion. (2 marks) ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ Section B: Atomic World Q.2: Multiple Choice Questions 2.1 Which of the following can be deduced from the result of Rutherford’s scattering experiment? (1) An atom is mainly empty space. (2) An electron occupies certain discrete orbits only. (3) The total energy of an electron in its orbit remains constant. A. (1) only C. (1) and (2) only 2.2 B. (3) only D. (1) and (3) only A B C D Which of the following photons may excite a hydrogen atom from the ground state to the first excited state? (1) A photon with energy 3.4 eV (2) A photon with energy 10.2 eV (3) A photon with energy 12.0 eV A. (1) only B. (2) only C. (1) and (2) only D. (2) and (3) only P.4 A B C D 2.3 Which of the following can be explained by the Bohr’s model? (1) Discrete bright lines are observed in the emission spectrum of hydrogen atom. (2) Dark lines are observed in the absorption spectrum of hydrogen atom. (3) The interference pattern observed using electrons. 2.4 A. (1) and (2) only B. (1) and (3) only C. (2) and (3) only D. (1), (2) and (3) B C D When a light beam is directed at a copper plate, photoelectrons are emitted. If the wavelength of the light beam is increased but the intensity of the light source remains unchanged, what is the change in the maximum kinetic energy of the photoelectrons and the number of photoelectrons emitted per second? A. B. C. D. 2.5 A maximum kinetic energy remains unchanged remains unchanged decreases decreases number of photoelectrons emitted remains unchanged A increases remains unchanged increases B C D In an experiment studying photoelectric effect, a graph showing the relationship between the stopping potential and the frequency of the incident light is obtained. Estimate Planck constant from the above graph. A. 5.3 × 10–34 J s B. 6.0 × 10–34 J s C. 6.7 × 10–34 J s A B C D D. 7.4 × 10–34 J s 2.6 2.7 Bohr’s theory quantizes the energy of electrons in orbits. Therefore the angular momentum of electrons is also quantized. Consider an electron in a hydrogen atom, determine the linear velocity of this electron which is revolving around the nucleus in the second orbit (quantum number 2). The radius of the orbit is 0.212 nm. A. 1.09 106 m s–1 B. 1.64 106 m s–1 A B C D C. 2.19 106 m s–1 D. 4.92 106 m s–1 Which of the following statements about transmission electron microscopes (TEM) are correct? (1) A TEM has a higher resolution than an optical microscope because fast moving electrons have much shorter wavelengths than visible light. (2) A TEM can have a higher resolution by using electrons with lower kinetic energy. (3) TEM can image non-conducting samples. A. (1) and (2) only B. (1) and (3) only C. (2) and (3) only D. (1), (2) and (3) P.5 A B C D 2.8 Which of the following statements about nano particles is/are incorrect? (1) The colour of nano particles may depend on their size. (2) Nano particles of a material have a larger total surface area to volume ratio than the bulk form of the same material. (3) All nano particles are man-made. A. (1) only B. (3) only C. (1) and (2) only D. (2) and (3) only A B C D Q.2: Structured question (a) The following figure shows some of the energy levels for an iron atom. (i) Draw another arrow on the above figure to represent the smallest energy change possible for an electron moving between two of the energy levels shown. The electron energy change selected must result in energy being emitted from the atom. Label this arrow B. (1 mark) (ii) In the above figure, when the energy change labelled A occurs, a photon is emitted. What is the wavelength of the photon? (2 marks) ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ (iii) What type of radiation, infrared radiation, visible light or X-ray, does this photon belong to? (1 mark) ____________________________________________________________________________________________ (b) Explain why photons of this wavelength would be suitable to investigate the structure of a metallic crystal. (2 marks) ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ P.6 (c) (i) Electrons can also be made to investigate the structure of a metallic crystal. To do so, the electrons are to be accelerated by a potential difference V. When the electrons are accelerated to a certain speed v, its de Broglie wavelength will be 1.5 × 10-10 m and will be suitable for investigation purpose. Calculate the speed v required for such a de Broglie wavelength. (2 marks) ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ (ii) Calculate the potential difference V required. (2 marks) ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ Section C: Energy and Use of Energy Q.3: Multiple Choice Questions 3.1 Lamp X has a higher input power than lamp Y. Which of the following statements must be correct? (1) Lamp X is brighter than lamp Y. (2) The cost of electricity of using lamp X is higher than that of lamp Y. (3) Lamp Y is more energy efficient than lamp X. 3.2 A. (1) only B. (2) only C (1) and (2) only D. (1), (2) and (3) A B C D X is a point on a plane surface as shown. The surface can be rotated about axle PQ. A point source of light is 2.5 m away from X and the light from the source hits X perpendicularly. Which of the following can reduce the illuminance at X by half? (1) Reduce the luminous flux of the light source by half. (2) Rotate the surface about PQ by 30. (3) Increase the distance between X and the light source to 5 m. A. (1) only B. (3) only C. (1) and (2) only D. (1), (2) and (3) P.7 A B C D 3.3 Which of the following is/are (an) advantage(s) of an electric hotplate over an induction cooker? (1) An electric hotplate heats food without generating heat itself. (2) An electric hotplate is more energy efficient. (3) An electric hotplate can be used with non-metallic pots. 3.4 A. (2) only B. (3) only C. (1) and (3) only D. (1), (2) and (3) A B C D The table below shows the input powers and the cooling capacities of air-conditioners X and Y. Input power / W Cooling capacity / W X 800 1600 Y 1200 2400 Which of the following statements about X and Y is/are correct? 3.5 3.6 3.7 3.8 (1) Y cools a room faster than X does. (2) Y consumes more energy than X does in cooling a room. (3) Y removes more heat from the room to the outside than X does within the same period of time. A. (1) only B. (2) only C. (1) and (3) only D. (1), (2) and (3) A B C D The total area of the exterior walls (excluding windows) and the roof of a building is 6000 m2. The total rate of heat transfer through the walls and the roof is 12.5 kW while the rate of heat transfer through the windows of the building is 185 kW. If the Overall Thermal Transfer value (OTTV) of the building is 27.5 W m–2, what is the total area of the windows? A. 486 m2 B. 571 m2 C. 914 m2 D. 1182 m2 A B C D In a hydroelectric power plant, some water falls through a vertical distance of 90 m and drives the turbine. Suppose the rate of water flow is 2 × 105 kg s−1 and the overall efficiency of the turbine is 40%. Estimate the output power. A. 7.20 MW B. 18.0 MW C. 70.6 MW D. 106 MW A B C D Which of the following statements about binding energy per nucleon (Eb/A) is/are correct? (1) The higher the value of the (Eb/A), the more unstable the nucleus is. (2) A heavier nucleus must have a higher value of the (Eb/A). (3) The Eb equals the work done required to break the nucleus into its constituent nucleons. A. (1) only B. (3) only C. (1) and (2) only D. (2) and (3) only A B C D A B C D Which of the following factors will affect the power output of a wind turbine? (1) the length of the blades (2) the direction of the wind (3) the wind speed A. (1) and (2) only B. (1) and (3) only C. (2) and (3) only D. (1), (2) and (3) P.8 Q.3: Structured question An electric vehicle is propelled by an electric motor. A battery cell converts chemical energy into electrical energy which is used to operate the motor. Suppose an electric car has a battery pack with an energy capacity of 25 kWh. (a) The battery should be charged at a voltage of 220 V. If the average charging current is 35 A, how long (in hours) does it take to charge the battery pack fully? (2 marks) ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ (b) If one unit of electrical energy costs $ 0.98, calculate the cost of recharging the battery pack fully. (1 mark) ____________________________________________________________________________________________ ____________________________________________________________________________________________ (c) Test results indicate that when the electric vehicle is travelling at a uniform speed of 40 km h -1 along a straight horizontal road, the total energy required to overcome air resistance and friction is 240 kJ per km of distance travelled. Assume that 60 % of the energy supplied by the battery pack is usesd to overcome air resistance and friction. (i) Based on the test results, estimate the farthest distance travelled by the vehicle when travelling at a uniform speed of 40 km h-1. (2 marks) ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ (ii) State one reason why the actual distance travelled is smaller than that found in (c) (i) when the vehicle is put to use in practical situations. (1 mark) ____________________________________________________________________________________________ ____________________________________________________________________________________________ (d) An electric vehicle has installed a regenerative braking system. Explain the function of such a system. (2 marks) ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ (e) State two advantages of an electric vehicle other than its high efficiency. (2 marks) ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ P.9 End of Paper 2 List of data, formulae and relationships Data R = 8.31 J mol1 K1 NA = 6.02 1023 mol1 g = 9.81 m s2 (close to the Earth) G = 6.67 1011 N m2 kg2 c = 3.00 108 m s1 e = 1.60 1019 C me = 9.11 1031 kg 0 = 8.85 1012 C2 N1 m2 0 = 4 107 H m1 u = 1.661 1027 kg (1 u is equivalent to 931 MeV) 11 AU = 1.50 10 m ly = 9.46 1015 m pc = 3.09 1016 m = 3.26 ly = 206 265 AU = 5.67 108 W m2 K4 h = 6.63 1034 J s molar gas constant Avogadro constant acceleration due to gravity universal gravitational constant speed of light in vacuum charge of electron electron rest mass permittivity of free space permeability of free space atomic mass unit astronomical unit light year parsec Stefan constant Planck constant Rectilinear motion For uniformly accelerated motion: v = s = v2 = u + at 1 ut + at 2 2 u2 + 2as Mathematics Equation of a straight line y = mx + c Arc length = r Surface area of cylinder = 2rh + 2r2 Volume of cylinder = r2h Surface area of sphere = 4r2 Volume of sphere 4 = πr 3 3 For small angles, sin tan (in radians) Astronomy and Space Science Energy and Use of Energy GMm U = r P = AT4 f v λ f0 c λ0 gravitational potential energy E Stefan’s law A(TH TC ) Q =k d t k U= d 1 P = Av 3 2 Doppler effect A illuminance Atomic World Medical Physics 1 m0 v max 2 = hf Einstein’s photoelectric equation 2 4 1 m e 13 .6 En = 2 2e 2 = 2 eV n 8h 0 n energy level equation for hydrogen atom h h = = de Broglie formula p mv = 1.22 λ d Rayleigh criterion (resolving power) 1.22 λ d 1 power = f L = 10 log rate of energy transfer by conduction thermal transmittance U-value maximum power by wind turbine Rayleigh criterion (resolving power) power of a lens I I0 intensity level (dB) Z = c acoustic impedance 2 I (Z Z1 ) = r = 2 intensity reflection coefficient I 0 (Z 2 Z1 ) 2 I = I0ex transmitted intensity through a medium P.8 Q1Q 2 A1. E = mcT energy transfer during heating and cooling D1. F= A2. E = lm energy transfer during change of state D2. E= A3. pV = nRT equation of state for an ideal gas D3. V= Q 4π 0 r electric potential due to a point charge A4. pV = 1 Nmc 2 3 kinetic theory equation D4. E= V d electric field between parallel plates (numerically) A5. EK = 3RT 2N A molecular kinetic energy D5. I = nAvQ general current flow equation D6. R= force D7. R = R1 + R2 v p = t t 4 π 0 r 2 Q 4π 0 r 2 l Coulomb’s law electric field strength due to a point charge resistance and resistivity A B1. F =m B2. moment = F d moment of a force D8. B3. EP = mgh gravitational potential energy D9. P = IV = I2R power in a circuit B4. EK = kinetic energy D10. F = BQv sin force on a moving charge in a magnetic field B5. P = Fv = mechanical power D11. F = BIl sin force on a current-carrying conductor in a magnetic field B6. a= centripetal acceleration D12. V= B7. F= Newton’s law of gravitation D13. B= D14. B= fringe width in double-slit interference D15. =N D16. Vs N s Vp N p ratio of secondary voltage to primary voltage in a transformer E1. N = N0ekt law of radioactive decay E2. t1 = 1 mv 2 2 W t v2 = 2r r Gm1 m 2 r 2 λD a C1. y = C2. d sin = n diffraction grating equation C3. 1 1 1 = u v f equation for a single lens 1 1 1 = + R R1 R 2 2 BI nQt 0 I 2 πr 0 NI l t ln 2 k resistors in series resistors in parallel Hall voltage magnetic field due to a long straight wire magnetic field inside a long solenoid induced e.m.f. half-life and decay constant E3. A = kN activity and the number of undecayed nuclei E4. E = mc2 mass-energy relationship P.9 F6 Physics Mock Exam (12-13) Paper 2 Suggested Answers Section A: Astronomy and Space Science 1-5 C D C C D 6-8 A A C 9. (a) d = tan 4.5 1.3 1.50 1011 d = 1.535 × 1010 m Length of tail = 2d = 3.07 × 107 km (b) (c) 1M 1A OR: Length of tail = 1.3 1.50 1011 9 180 = 3.06 × 1010 m = 3.06 × 107 km No, because Halley is not fixed on the celestial sphere. By Kepler’s third law, a3 T2 aEarth3 TEarth2 13 (in AU) 12 (in Earth years) 1M 1A 1A 1A 1M 3 ∴ a 75.32 AU = 17.8 AU The semimajor axis of Halley’s orbit is 17.8 AU. (d) 8.75 x 1010 + d = 2 x 17.8 x 1.50 x 1011 The farthest distance d = 5.25 x 1012 m (e) The speed of Halley is higher at point Q than that at point R. Since point Q is closer to the Sun than point R . (f) v 2GM r 2 6.67 10 11 1.99 1030 5.51 10 4 m / s 8.75 1010 1A 1M+1A 1A 1M+1A Explanations to selected MC 1.1 Since the center of the circles is near the sea level, the north celestial pole is near the sea level, so the latitude of the place P must be near 0o (recall that NCP or SCP is at the same angle as the latitude of the observer). 1.2 Brightness b = L / 4r2. 1.4 For blackbody radiation, maximum amount of radiation occurs at wavelength where max 1 T or max = constant / T => fmax = c/max T 1.5 Since T2 r3, so T1 r ( 1 )3 / 2 T2 r2 v1 1r1 T2 r1 1 v2 2 r2 T1r2 2 3/ 2 T2 r1 r2 r r 1 1 2 T1r2 r1 r2 r1 2 r2 1 r1 4 U 1 GMm / r1 r2 1 => U2 = 4U1 = 4E U 2 GMm / r2 r1 4 1.6 Statement 1, remember that absolute magnitude (as well as apparent magnitude) works backward, i.e. the higher the luminosity, the lower the absolute magnitude. Statement 2, if the difference of apparent magnitude of two stars is 5 (not 6), the brightness of one star is about 100 times the brightness of the other star. 1.7 GMm 1 GMm 1 m 1076 2 mv 2 8 8 3.6 10 2 4 10 2 Use Put M = 5.98 x 1024 kg, we get v = 968 m/s 1.8 Consider the Doppler effect: vr 0 c 40 000 = 8 (3 10 ) (656.1 10 9 ) Δλ = 0.088 nm Since the star is moving towards the Earth, the line should be blue-shifted. Section B: Atomic World 1-5 ABADD 9. (a) (b) (c) 6-8 A B B (i) -0.66 to –0.72 eV line marked as B, downward arrow. (1A) (ii) E = hc/ 7.06 x 1000 x 1.6 x 10-19 = 6.63 x 10-34 x 3 x 108 / (1M) = 1.76 x 10-10 m (1A) (iii) X-ray The wavelength is of order 10-10 m which is of same order as atomic spacing, (1M) producing significant and suitable diffraction and interference. (1M) (i) = h/mv 1.5 x 10-10 = 6.63 x 10-34 / (9.11 x 10-31 x v) (1M) v = 4.85 x 106 m/s (1A) (ii) eV = (1/2) mv2 1.6 x 10-19 V = (1/2) x 9.11 x 10-31 x (4.85 x 106)2 (1M) V = 67 V (1A) Explanations to selected MC 2.4 Increasing wavelength means decreasing fequency, so the energy of each photo E = hf decreases, hence the maximum KE is decreased since Kmax = hf - . If the intensity is unchanged, the total amount of energy is unchanged, thus the no. of photons is increased, resulting in an increase of photoelectrons. 2.5 e Vs = Kmax = hf - Vs = (h/e) f - /e So a graph of stopping potential against frequency is a straight line with slope = h/e nh 2.6 L = mevr = 2 9.11 10–31 v 0.212 10–9 = 2 6.63 10 34 2 v = 1.09 106 m s–1 Section C: Energy and Use of Energy MC 1-5 3. BABCD (a) 6-8 C B D Energy stored = 25 1 000 3 600 = 90 MJ E = VIt [1M] 90 106 = 220 35 t t = 11 688 s (3.25 hours) [1A] (b) Cost = 0.98 x 25 = $24.5 (c) (i) 25 x 3.6 x 106 x 0.6 = 240 x 103 x d (1M for 25 x 3.6 x 106 x 0.6) d = 225 km (1A) (ii) * More energy is required if the vehicle is travelling at a higher speed because the resistance will be higher. * The vehicle gains KE when it accelerates. * The vehicle gains PE when it climbs up. * Extra energy is needed when brakes are applied. (d) The regenerative braking system converts the kinetic energy of the car to electrical energy during braking (1A). This energy is stored in the battery. (1A) (e) Any TWO of the following * Electric vehicles are quiet when they are in operation. * Electric vehicles create less pollution problems. * Easier maintenance as there are less moving parts Explanations to selected MC 3.2 E F cos A 4r 2 Statement 1, if flux is reduced by half, illuminance E is reduced by half accordingly. Statement 2, if the surface is rotated by 30o, the illuminance is reduced by cos 30o = 0.866. Statement 3, if is increased to 5 m, i.e. doubled, the illuminance is reduced to 1/4 its initial value. 3.4 Y consumes the same amount of energy as X in cooling a room. For example, to remove 4800 J of energy from a room, Y needs 2s, and the electrical energy used is 2 x 1200 = 2400 J. X needs 3s and the electrical energy used is 3 x 800 = 2400 J. So statement 2 is incorrect. 3.5 3.6 27.5 = (12.5 x 103 + 185 x 103) / (6000 + A) A = 1182 m2 Output power = mgh / t x 0.4 = 2 x 105 x 9.81 x 90 x 0.4 = 70.6 MW 3.7 (1) The higher the value of the (Eb/A), the more stable the nucleus is. (2) A heavier nucleus may not have a higher value of the (Eb/A). In fact, the mid size nuclei have the greatest (Eb/A).