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VCE Physics: Common Exam Errors Revision Advice Exam advice. Common Exam Errors. Common Errors: Connected Bodies. Examples : Horse pulling a cart, Mass over edge pulls another along table. Error : Apply net force on system to each mass. Misuse internal forces. - PowerPoint PPT Presentation

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<ul><li><p>VCE Physics:</p><p>Common Exam ErrorsRevision AdviceExam advice</p></li><li><p>Common Exam Errors</p></li><li><p>Common Errors: Connected BodiesExamples: Horse pulling a cart, Mass over edge pulls another along table.Error: Apply net force on system to each mass. Misuse internal forces.</p><p>Consider: Questions 3 & 4 from 2010 Exam.</p></li><li><p>Average: 0.7 out of 2 (35%), Only 10% got 2 marks.Average: 1.1 out of 2 (55%), 51% got 2 marks. Consequential on Qn 3.Common errors: assume a = g or loss of GPE of mass 2 = gain in KE of mass 1</p></li><li><p>Common Errors: Connected BodiesMethod:Label all forces actingThe whole system and each mass of the system accelerates at the same rateApply Newtons 2nd Law: Net Force = Mass x Acceln applies to each mass in the system and to the whole system as well.Forces between masses in the system are examples of Newtons 3rd Law.</p></li><li><p>Acceln = aAcceln= am2gTTm1gNNet force on m1 equals T, but T is unknown, so use Net force on the system of two masses: Net force on (m1 and m2) = m2g, but Net F = Ma, so m2g = (m1 + m2) x a.Substituting, 0.10 x 10 = (0.1 + 0.4) x a, solve for a.Conseq Qn: use value of acceln. Two methods: i) Use equations of motion to find v, the calculate KE, or ii) Use Work Done by force on m1 = Gain in KE</p></li><li><p>Common Errors: Circular MotionExamples: Banked curves, crests in roadError: Include centripetal force as another force, misunderstand reaction force.</p><p>Consider: Questions 5 & 6 from 2010 Exam.</p></li><li><p>Average: 0.9 out of 2 (45%), 51% got zero)Average: 1.5 out of 3, 48% got 3, 48% got zero</p></li><li><p>Common Errors: Circular MotionExamples: Banked curves, crests in roadError: Include centripetal force as another force, misunderstand reaction force.</p><p>Method: Better to only refer to centripetal acceleration and then apply Newtons 2nd Law.</p><p>Consider: Questions 5 & 6 from 2010 Exam.</p></li><li><p>Vertically: mg = N Sin q, Horizontally: N Cos q = Net Force = ma = mv2/r, so combining: Tan q = gr/v2, now solve for angle.mgN</p></li><li><p>Common Errors: Reaction force and Apparent weightExamples: Platforms slowing down, landing on trampolineError: Confusing directions, and net force with actual forces.</p><p>Consider: Question 8 from 2009 exam.</p></li><li><p>Average: 1.4 out of 3, 43% full marks, 54% got zero.</p></li><li><p>Common Errors: Reaction force and Apparent weightExamples: Platforms slowing down, landing on trampolineError: Confusing directions, and net force with actual forces.Method: Define a direction as positive, Determine sign of acceleration, Draw in acting forces, Apply Newtons 2nd Law</p><p>Consider: Question 8 from 2009 exam.</p></li><li><p>Downwards as +ive Acceln = 2.0 m/s2mgReaction force from platform, NNet Force = mamg N = maN = mg ma, Solve for N</p></li><li><p>Common Errors: CollisionsExamples: Elastic, and inelastic collisions (both sticky and non-sticky)Error: Assume momentum temporarily goes into storage; assume all rebound collisions are elastic.</p><p>Consider: Questions 15 - 17 from 2010 Exam.</p></li><li><p>36% got full marks56% got full marks35% got full marks</p></li><li><p>Common Errors: CollisionsExamples: Elastic, and inelastic collisions (both sticky and non-sticky)Error: Assume momentum temporarily goes into storage; assume all rebound collisions are elastic.</p><p>Method: Include graphs on 2 page summary.</p><p>Consider: Questions 15 - 17 from 2010 Exam.</p></li><li><p>Common Errors: GravitationExamples: Satellite motionError: Confusion of net force with actual forces. Need for a tangential force.</p><p>Consider: Question 13 from 2009 Exam.</p></li><li><p>Average 0.8 out of 2, 44% got zero, 26% got full marks.Common faults: Tangential force; wrong label; two arrows</p></li><li><p>Common Errors: GravitationExamples: Satellite motionError: Confusion of net force with actual forces. Need for a tangential force.</p><p>Method: Emphasise: a force inwards is all that is necessary for circular motion - Keys on a string.</p><p>Consider: Question 13 from 2009 Exam.</p></li><li><p>Common Errors: Electric CircuitsExamples: Diode circuitsError: Dont realise diode restricts voltage.</p><p>Consider: Question 2 from 2010 Exam.</p></li><li><p>Average: 0.7 out of 2, 62% got zero, most assumed Total R = 700 ohm</p></li><li><p>Common Errors: Electric CircuitsExamples: Diode circuitsError: Dont realise diode restricts voltage.</p><p>Method: Do prac showing voltage across a LED is constant and independent of resistor values, while the LED is on.Draw current arrows and voltage drops, apply current and voltage rules.</p></li><li><p>I1 = I2 + I3 , 6 V = V1 + V2From graph V2 = 1.0 V, so V1 = 5.0 V, So using V = IR on 500 ohm resistor, current = 5.0 / 500 = 0.01 A,I = 10 mAAny follow up questions?I1I2I3V1V2</p></li><li><p>Common Errors: Electric CircuitsExamples: Diode circuitsError: Confused about voltage and current in series and parallel circuits.</p><p>Consider: Question 4 from 2009 Exam.</p></li><li><p>Average: 1.4 out of 3, 46% got zero, 41% got full marksMany said I = 12/60</p></li><li><p>Common Errors: Electric CircuitsExamples: Diode circuitsError: Confused about voltage and current in series and parallel circuits.</p><p>Method: Do prac measuring current and voltages in complex circuits, e.g. students each design and assemble a circuit for a set of LEDs and a resistor and measure voltage values and current through battery, then swap circuits and calculate the values for the new circuit. </p><p>Draw current arrows and voltage drops, then apply current and voltage rules.</p></li><li><p>I1I2V1V2I1 = I2 + I2, 12 V = V1 + V2. From diode graph V2 = 3 x 3.0 V = 9.0 V, so V1 = 12 - 9 = 3.0 V. Using V = IR, current through R2 = 3.0 / 60 I = 0.050 A = 50mA</p></li><li><p>Common Errors: Electromagnetic InductionExamples: Induced EMF with changing FluxError: Dont realise that only a changing magnetic flux induces an EMF.</p><p>Consider: Questions 8, 9 and 11 from 2010 Exam.</p></li><li><p>Average: 0.8 out of 2, 51% got zero, some drew sine waves, many missed the point of different gradients.Average: 0.4 out of 1, both Faraday and Lenz were accepted.</p></li><li><p>Average: 1.0 out of 2, 33% get zero, Many said the induced flux opposed the original flux rather than the change in flux. Others had right reason, but wrong direction.</p></li><li><p>Common Errors: Electromagnetic InductionExamples: Induced EMF with changing FluxError: Dont realise that only a changing magnetic flux induces an EMF.</p><p>Method: Demonstration as an POE, with students drawing graph of flux (with direction) and observing induced EMF.</p><p>Consider: Questions 8, 9 and 11 from 2010 Exam.</p></li><li><p>TimeFluxInduced EMF0 1Increasing steadilyConstant andbut rapidlylarge1 2ConstantZero2 4Decreasing steadilyConstant and but slowlysmallerTwo possible answers</p></li><li><p>Magnetic Flux through loopBeforeAfterChangeChange = Final Initial or Initial + Change = FinalInduced Magnetic FieldDirection of CurrentOpposes changeUse Hand Rule</p><p>Down the front: Q to P</p></li><li><p>Common Errors: Path DifferenceExamples: Double Slit Interference of LightError: Assuming path difference is along the screen</p><p>Consider: Question 4 from 2010 Exam.</p></li><li><p>Average: 1 out of 2 = 50%. 48% got zero.Two students are studying interference of light. They use a laser of wavelength 580 nm.</p></li><li><p>Common Errors: Path DifferenceExamples: Double Slit Interference of LightError: Assuming path difference is along the screen</p><p>Method: Draw the light paths. Determine the path difference at specific points in multiples of l/2. Avoid stock formulae.</p><p>Consider: Question 4 from 2010 Exam.</p></li><li><p>Y is the next node after the antinode at X, so the path difference has increased by l/2.Path diff for Y = Path Diff for X + (580 / 2) = 1160 + 290 nm = 1450 nmTwo students are studying interference of light. They use a laser of wavelength 580 nm.</p></li><li><p>Common Errors: Momentum and energy of photons and electronsExamples: Comparing diffraction patterns between electrons and X-rays.Error: Assume if momenta of both are the same, then their energies are also the same.</p><p>Consider: Question 10 from 2010 Exam.</p></li><li><p>Average: 0.6 out of 3, 20%</p></li><li><p>Common Errors: Momentum and energy of photons and electronsExamples: Comparing diffraction patterns between electrons and X-rays.Error: Assume that if momenta of both are the same, then their energies are also the same.</p><p>Method: Draw up concept map linking quantities with relationships.</p><p>Consider: Question 10 from 2010 Exam.</p></li><li><p>ElectronPhotonMomentumWavelengthMomentumVelocity, vKinetic EnergyEnergySpeed, cpl = h/plp = h/lpp = mvE = p2/2mE = hc/lE = pcKE = mv2For Electrons: KE has to be in Joules to determine its momentum and wavelength.For Photons: Energy can be in either eV or Joules to determine its wavelength.</p></li><li><p>Steps: KE in eV to KE in Joules to electron momentum to electron wavelength.Wavelengths are the same, so then Wavelength to photon energy in eV</p></li><li><p>Revision Advice for Students</p></li><li><p>Revision Advice for StudentsPrepare a one page summary as soon as you finish an Area of Study,Use it with extra problems until the weeks before the exam,Maintain a regular routine of doing exam type problems after finishing an Area of Study,Two weeks before the exam prepare the first draft of the two page summary.</p></li><li><p>Revision Advice for StudentsIn the two weeks before the exam:Use the draft with past exam and trail papers,For June exam, one exam 90 min paper per day under exam conditions at home, for a fortnight is doable,Evaluate performance after each exam and revise draft of two page summary accordingly.</p></li><li><p>Exam Advice for StudentsUse the 15 minute reading productively,Attitude: Remember if you are finding the exam fairly hard, dont panic, because the rest of the state is probably also finding it hard. The reverse also applies.Read the Question Carefully: The exam will have many instances where you have to read a graph or interpret data. In many cases the values will need to be converted to SI units, e.g. cm m, kN N, MPa Pa.</p></li><li><p>Exam Advice for StudentsHighlight data and important information as you read the question. Show working every time.Written response: Answer in point form. Dont look for complexities in the question. Assume the simplest explanation.</p></li></ul>