Trial Examination VCE Physics Unit 1. Written Examination. Suggested Solutions

Transcription

1 Trial Examination 203 VCE Physics Unit Written Examination Suggested Solutions Neap Trial Exams are licensed to be photocopied or placed on the school intranet and used only within the confines of the school purchasing them, for the purpose of examining that school s students only. They may not be otherwise reproduced or distributed. The copyright of Neap Trial Exams remains with Neap. No Neap Trial Exam or any part thereof is to be issued or passed on by any person to any party inclusive of other schools, non-practising teachers, coaching colleges, tutors, parents, students, publishing agencies or websites without the express written consent of Neap. Copyright 203 Neap ABN Pelham St Carlton VIC 3053 Tel: (03) Fax: (03) TEVPHYU_SS_203.FM

2 AREA OF STUDY NUCLEAR PHYSICS AND RADIOACTIVITY Question (6 marks) a. The atomic number is the number of protons while the mass number contains the number of protons and neutrons. b. As the number of protons increases, the ratio has to be greater than one (more than one neutron for every proton) in order to maintain stability. 25 With lead the ratio is =.52, so a ratio greater than one is needed for the heavier elements. 82 c. N needs to deviate from N = Z upwards N = Z Z 2 marks Question 2 (4 marks) a. Some factors that could be listed include length of time of exposure, type of radiation (α versus γ) and method of exposure (ingested/inhaled/external only). 2 marks Any other reasonable/plausible explanation b. If the exposure to the same radiation is of relatively short duration then one would expect short-term effects. Examples of short-term effects might include burns or vomiting/nausea. Increasing the time of exposure increases the risk of long-term effects becoming a reality. An example of a long-term effect might be some form of cancer. Any other reasonable/plausible alternative 2 TEVPHYU_SS_203.FM Copyright 203 NEAP

3 Question 3 (0 marks) a. An alpha emitter will ionise the air much more readily than the other sources. The plastic case (and air) will stop the alpha radiation, whereas beta and gamma would be able to penetrate the plastic and leave the container Np b. Am + He + 2 marks γ is optional c. Am-24 is an artificial type made in a nuclear reactor. It is man-made. Artificial isotopes tend to be much less stable than natural ones and as a consequence have a shorter half-life. d. Transmutation is the conversion of one element into another, in this case by the absorption of a neutron into the nucleus. Neutron absorption is more effective as it has no charge and would not be repelled like a positive alpha particle would be. 239 e. 94 Pu+ 2 0n 94Pu 95 Am + β + γ 2 marks -- mark each for correct section 2 Question 4 (8 marks) a. y γ becquerels half-life point x time (min) 3 marks each for correct labels, plot and line of best fit b. See graph above in a. c. 4 half-lives = = 46.9 = 47 g 2 d. accept anywhere between minute range e. Ava is correct. The disintegration rate is independent of the temperature of the sample. Copyright 203 Neap TEVPHYU_SS_203.FM 3

4 Question 5 (0 marks) a. Positive charge Negative charge No charge α β γ Fastest speed Medium speed Slowest speed γ β α Strongest ioniser Medium ioniser Weakest ioniser α β γ Long-range penetration Mid-range penetration Shortest-range penetration γ β α 3 marks for each correct column b. Energy = absorbed dose mass = = 8 06 = 8 MJ 2 marks for calculation, for putting answer in correct form c. γ-rays have high penetrating power and can easily pass through the containers and sterilise the food deep inside. Alpha and beta particles may be stopped. They also can make the food unsafe to eat as they have higher levels of ionisation. (optional) d. Dose equivalent takes into the fact that different forms of radiation have different levels of ionisation and thus do different levels of damage to humans. The quality factor (QF) takes this into account. Therefore an alpha particle has a higher QF than gamma since it ionises much more when compared to either alpha or beta particles. AREA OF STUDY 2 ELECTRICITY Question a. I capacity = time 450 ma = h = 3 ma P= V I= 3.7 V 3 ma = mw b. c. Q = I t = 3 ma = 620 C R = V Ī V = ma = 233 Ω 4 TEVPHYU_SS_203.FM Copyright 203 NEAP

5 d. Since less time is used the current must be greater. Greater current of the same voltage means the resistance must be smaller. Question 2 a. R total R total V = -- I 2 V = ma = 40 Ω = = Ω R total b. c. d. I= VR 2 V = Ω = 60 ma P= V I = 2 V 300 ma = 3.6 W E t = -- P kwh = kw = 278 h Question 3 a. At first the resistance is very high since there is very little current below 0.8 V. Then it quickly become smaller and it reaches R = 0 Ω (or very low) at V =.2 V. b. LED is non-ohmic because its resistance changes as the voltage increases. c. V across the LED =.2 V, from graph V across R = 6.2 = 4.8 V Question 4 a. There is a potential difference between the heating elements (240 V) and the ground (0 V). As you put in the knife you provide a pathway for the current to flow from 240 V to 0 V. This current though your body can be fatal. b. The earth connection will not help because it is designed to direct current away from the exterior of the toaster, not its internal workings. The earth-leak switch will help because it will cut the current very quickly as it detects some current going to earth. Copyright 203 Neap TEVPHYU_SS_203.FM 5

6 AREA OF STUDY 3 DETAILED STUDIES (2 marks for each correct answer) Detailed study Astronomy Question D Constellations are patterns of stars only visible from our perspective. In reality. these stars could be varying distances from Earth. Question 2 B Because of the Earth s rotation around the Sun, the sidereal day is 4 minutes shorter than 24 hours. The 24-hour day is defined with our position relative to the Sun. Question 3 B If you have the South Celestial Pole in the Zenith, all stars would make diurnal motions parallel to the horizon. Question 4 C The CSP is observed 38 above the Southern horizon. Question 5 C Only the phases of Mercury and Venus are unable to be explained in a Ptolomeic system, as the phases result from their rotation around the Sun. Question 6 B As the period of orbital rotation of the Moon is equal to the rotation around its own axis, the Moon always shows the same face towards the Earth. This is not a coincidence, but a result of billions of years of gravitational interaction between the Moon and the Earth. Question 7 C A nebula is a volume of space filled with cool dust and gas that can obscure the starlight from behind it. Some nebulae are lit from within by young stars formed within the nebula. Question 8 A This is a refracting telescope. Galilean telescopes use a concave lens for the eyepiece. Newtonian and reflecting telescopes use mirrors for their objectives. Question 9 75 mm = 5 mm 5 B Question 0 D A greater diameter of the objective will allow more light to enter the telescope. This means more information and hence more detail. Question D Data collection in modern telescopes use CCDs and computers to record images and data. 6 TEVPHYU_SS_203.FM Copyright 203 NEAP

7 Question 2 D The Earth s atmosphere is mostly opaque in the part of the spectrum from 0 m and beyond. Detailed study 2 Astrophysics Question C The relationship is --- and Graph C best approximates this. r 2 Question 2 A The total power output remains more or less constant; it just gets spread over a larger area as the distance increases. Question 3 D The relationship is quartic and this is best given by Graph D. Question 4 B The parsec is defined using this right-angled triangle. Question 5 D AU is equal to the 50 million kilometres of Earth s radius, so using trigonometry: tan( 0.5 ) = a = tan( 0.5 ) = 5 AU adjacent (a) Question 6 A The mass of Jupiter is not sufficient to enable gravity to start the required nuclear reactions. Question 7 C Fusion is the principal reaction in a star. Question 8 D The other sequences are incorrect. Question 9 A The change in frequency for a wave is known as the Doppler effect. Question 0 B The visible light would move towards the blue end of the visible spectrum. Question D Spiral galaxies have a minimum of two arms and elliptical galaxies have older-type stars. Question 2 A It is thought that slight density variations in the mass allowed matter to clump together to eventually form galaxies. Copyright 203 Neap TEVPHYU_SS_203.FM 7

8 Detailed study 3 Energy from the nucleus Question B The nucleus is held together by the strong nuclear force and electrons are held to the nucleus by the electrostatic force of attraction. Question 2 A The binding energy is a measure of the energy required to pull nucleons apart. Question 3 C Fusion of light elements make the atom more stable; heavier elements are more unstable and fission into smaller elements increases their stability. Question 4 A The energy produced per day is W = J, and using E = mc 2, m J = = kg. ( ) 2 Question 5 Convert ev to J. D = J. Then divide total energy by energy per reaction: = reactions Question 6 D U-235 requires slow-moving neutrons while Pu-239 can capture fast-moving neutrons. Question 7 B Component S is the heat exchanger. Question 8 C Component Q are the control rods, and their main function is to slow down the reaction. Question 9 D Component T is the containment structure. Question 0 A U-235 and Pu-239 are most commonly used in nuclear reactors. Question D X is a neutron, and three neutrons are needed to complete the equation. Energy is also released. Question 2 B Current technology cannot sustain the fusion process. 8 TEVPHYU_SS_203.FM Copyright 203 NEAP

9 Detailed study 4 Investigations: Flight Question C Drag and thrust require a forward velocity and engine power. Neither are present in the balloon. Question 2 D Weight and drag are not usually described as reaction forces. Thrust in a jet engine is a reaction to the forceful emission of gases from the engine, and lift can be explained as the reaction to the downward force on the air by the wing. Question 3 B Conservation of momentum provides an alternative, or complimentary, explanation for lift: the wing causes a downward impulse on the air as it moves. This is matched by an equal and opposite change impulse on the wing/aircraft, thus creating lift. Question 4 D According to Bernoulli s principle, the pressure in a fluid is proportional to the velocity of the fluid. Question 5 C Since L is proportional to v 2, lift will increase fourfold. Question 6 A According to Bernoulli s principle, the faster air at the end of tube B will result in localised low pressure, and so the higher normal pressure will push the ink up into tube B. Question 7 weight = m g = = B and to achieve take-off a force greater than weight is required. Question 8 C The lower air densities at higher altitude reduce the drag and therefore less power is required to maintain airspeed. Question kg N C P = F v 40 MW = F 250 m s F = 560 kn Question 0 C The graph shows a straight line with a positive gradient for values below 0, but not going through the origin of the graph. Copyright 203 Neap TEVPHYU_SS_203.FM 9

10 Question C Stall is defined as the angle of attack at which the value for lift begins to decline. Question 2 D The increased drag would cause a reduced lift on the left-hand side of the plane, hence it would rotate anti-clockwise. In addition to this, the same drag increase would result in a reduction of torque on the left wing, causing the plane to turn left. Detailed study 5 Investigations: Sustainable energy sources Question B Nuclear energy is not renewable because uranium is a finite resource that cannot be replenished. Question 2 C maximum power at V = V and I =.6 A P = V I = 0.6 W Question 3 Question 4 Question 5 Question 6 A output efficiency = % input ( 0.72 W 00) = % 600 = 2% B 250 0% = 25 W m 2 25 W m 2 0 h = 250 W h = 0.25 kwh m = 80 m C 20 kwh = kj per year MJ = homes MJ B input = 29 MJ kg kg = MJ ouput = MJ MJ efficiency = = 8.6 % MJ 0 TEVPHYU_SS_203.FM Copyright 203 NEAP

11 Question 7 C.6 GW = about 500 turbines 3 MW Question 8 D In an effort to reduce Australia s CO 2 pollution, the government wants to close the most carbon-intensive power stations. Question 9 B Variable wind speeds mean that the average power output is always lower than the maximum. Question 0 D Since P is proportional to v 3, power output will increase 2 3 = 8 times if the wind speed doubles. Question A The differential heating of the atmosphere causes high and low pressure areas which leads to air movement. This in turn rotates the wind turbine and generates electricity. Question 2 D Replacing all fossil fuels would require a mixture of many different sources of renewable energy. Detailed study 6 Medical physics Question D X-ray has been around the longest. Question 2 A Ultrasounds typically have frequencies greater than MHz. Question 3 C The frequency remains constant, and since the speed increases as it goes from fat to muscle, the wavelength must also increase. Question 4 B X-rays can damage cells and so potentially pose a risk to a foetus. Question 5 B Bundle A must be coherent and bundle B can be incoherent. Question 6 B Increasing the number of fibres (bundles) causes the image quality to improve. Copyright 203 Neap TEVPHYU_SS_203.FM

12 Question 7 C Laser light has a much narrower wavelength than ordinary visible light. Question 8 A MRIs involve emission and detection of radio waves. Question 9 C For the radioisotope to work effectively it needs a half-life that is at least in the hours range. Question 0 D Bones absorb X-rays but not gamma-rays. Question D When a nucleus is deficient in neutrons a proton may decay into a neutron and positron. Question 2 C Plastic aprons are not a safety measure for dealing with X-rays. 2 TEVPHYU_SS_203.FM Copyright 203 NEAP