1. VCE Physics: Common Exam Errors Revision Advice Exam advice Resources

2. Common Exam Errors

3. 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. Consider: Questions 3 & 4 from 2010 Exam.

4. 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 Q’n 3. Common errors: assume a = g or loss of GPE of mass 2 = gain in KE of mass 1

5. Common Errors: Connected Bodies Method: 1.Label all forces acting 2.The whole system and each mass of the system accelerates at the same rate 3.Apply Newton’s 2nd Law: Net Force = Mass x Accel’n applies to each mass in the system and to the whole system as well. 4.Forces between masses in the system are examples of Newton’s 3rd Law.

6. Accel’n = a m2gm2g T T m1gm1g N Net force on m 1 equals T, but T is unknown, so use Net force on the system of two masses: Net force on (m 1 and m 2 ) = m 2 g, but Net F = Ma, so m 2 g = (m 1 + m 2 ) x a. Substituting, 0.10 x 10 = (0.1 + 0.4) x a, solve for a. Conseq Q’n: use value of accel’n. Two methods: i) Use equations of motion to find v, the calculate KE, or ii) Use Work Done by force on m 1 = Gain in KE

7. Common Errors: Circular Motion Examples: Banked curves, crests in road Error: Include centripetal force as another force, misunderstand reaction force. Consider: Questions 5 & 6 from 2010 Exam.

8. Average: 0.9 out of 2 (45%), 51% got zero) Average: 1.5 out of 3, 48% got 3, 48% got zero

9. Common Errors: Circular Motion Examples: Banked curves, crests in road Error: Include centripetal force as another force, misunderstand reaction force. Method: Better to only refer to centripetal acceleration and then apply Newton’s 2 nd Law. Consider: Questions 5 & 6 from 2010 Exam.

10. Vertically: mg = N Sin , Horizontally: N Cos  = Net Force = ma = mv 2 /r, so combining: Tan  = gr/v 2, now solve for angle. mg N

11. Common Errors: Reaction force and Apparent weight Examples: Platforms slowing down, landing on trampoline Error: Confusing directions, and net force with actual forces. Consider: Question 8 from 2009 exam.

13. Average: 1.4 out of 3, 43% full marks, 54% got zero.

14. Common Errors: Reaction force and Apparent weight Examples: Platforms slowing down, landing on trampoline Error: Confusing directions, and net force with actual forces. Method: Define a direction as positive, Determine sign of acceleration, Draw in acting forces, Apply Newton’s 2 nd Law Consider: Question 8 from 2009 exam.

15. Downwards as +ive Accel’n = 2.0 m/s 2 mg Reaction force from platform, N Net Force = ma mg – N = ma N = mg – ma, Solve for N

16. Common Errors: Collisions Examples: Elastic, and inelastic collisions (both sticky and non-sticky) Error: Assume momentum temporarily goes into ‘storage’; assume all rebound collisions are elastic. Consider: Questions 15 - 17 from 2010 Exam.

18. 36% got full marks 56% got full marks 35% got full marks

19. Common Errors: Collisions Examples: Elastic, and inelastic collisions (both sticky and non-sticky) Error: Assume momentum temporarily goes into ‘storage’; assume all rebound collisions are elastic. Method: Include graphs on 2 page summary.

20. Common Errors: Gravitation Examples: Satellite motion Error: Confusion of net force with actual forces. Need for a tangential force. Consider: Question 13 from 2009 Exam.

21. Average 0.8 out of 2, 44% got zero, 26% got full marks. Common faults: Tangential force; wrong label; two arrows

22. Common Errors: Gravitation Examples: Satellite motion Error: Confusion of net force with actual forces. Need for a tangential force. Method: Emphasise: a force inwards is all that is necessary for circular motion - “Keys on a string”.

23. Common Errors: Electric Circuits Examples: Diode circuits Error: Don’t realise diode limits voltage. Consider: Question 2 from 2010 Exam.

24. Average: 0.7 out of 2, 62% got zero, most assumed Total R = 700 ohm

25. Common Errors: Electric Circuits Examples: Diode circuits Error: Don’t realise diode limits voltage. 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.

26. I 1 = I 2 + I 3, 6 V = V 1 + V 2 From graph V 2 = 1.0 V, so V 1 = 5.0 V, So using V = IR on 500 ohm resistor, current = 5.0 / 500 = 0.01 A, I = 10 mA Any follow up questions? I1I1 I2I2 I3I3 V1V1 V2V2

27. Common Errors: Electric Circuits Examples: Diode circuits Error: Confused about voltage and current in series and parallel circuits. Consider: Question 4 from 2009 Exam.

29. Average: 1.4 out of 3, 46% got zero, 41% got full marks Many said I = 12/60

30. Common Errors: Electric Circuits Examples: Diode circuits Error: Confused about voltage and current in series and parallel circuits. 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. Draw current arrows and voltage drops, then apply current and voltage rules.

31. I1I1 I2I2 V1V1 V2V2 I 1 = I 2 + I 2, 12 V = V 1 + V 2. From diode graph V 2 = 3 x 3.0 V = 9.0 V, so V 1 = 12 - 9 = 3.0 V. Using V = IR, current through R 2 = 3.0 / 60 I = 0.050 A = 50mA

32. Common Errors: Electromagnetic Induction Examples: Induced EMF with changing Flux Error: Don’t realise that only a changing magnetic flux induces an EMF. Consider: Questions 8, 9 and 11 from 2010 Exam.

34. 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.

35. 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.

36. Common Errors: Electromagnetic Induction Examples: Induced EMF with changing Flux Error: Don’t realise that only a changing magnetic flux induces an EMF. Method: Demonstration as an POE, with students drawing graph of flux (with direction) and observing induced EMF. Consider: Questions 8, 9 and 11 from 2010 Exam.

37. TimeFluxInduced EMF 0 – 1Increasing steadilyConstant and but rapidlylarge 1 – 2ConstantZero 2 – 4Decreasing steadilyConstant and but slowlysmaller Two possible answers

38. Magnetic Flux through loop BeforeAfterChange Change = Final – Initial or Initial + Change = Final Induced Magnetic FieldDirection of Current Opposes change Use Hand Rule Down the front: Q to P

39. Common Errors: Path Difference Examples: Double Slit Interference of Light Error: Assuming path difference is along the screen Consider: Question 4 from 2010 Exam.

40. Average: 1 out of 2 = 50%. 48% got zero. Two students are studying interference of light. They use a laser of wavelength 580 nm.

41. Common Errors: Path Difference Examples: Double Slit Interference of Light Error: Assuming path difference is along the screen Method: Draw the light paths. Determine the path difference at specific points in multiples of /2. Avoid stock formulae. Consider: Question 4 from 2010 Exam.

42. Y is the next node after the antinode at X, so the path difference has increased by  /2. Path diff for Y = Path Diff for X + (580 / 2) = 1160 + 290 nm = 1450 nm Two students are studying interference of light. They use a laser of wavelength 580 nm.

43. Common Errors: Momentum and energy of photons and electrons Examples: Comparing diffraction patterns between electrons and X-rays. Error: Assume if momenta of both are the same, then their energies are also the same. Consider: Question 10 from 2010 Exam.

44. Average: 0.6 out of 3, 20%

45. Common Errors: Momentum and energy of photons and electrons Examples: 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. Method: Draw up concept map linking quantities with relationships.

46. ElectronPhoton MomentumWavelengthMomentum Velocity, vKinetic EnergyEnergySpeed, c p = h/p p = h/ p p = mvE = p 2 /2mE = hc/ E = pc KE = ½ mv 2 For 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.

47. 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

48. Revision Advice for Students Vicphysics Vicphysics The Students page has: Several links to websites with advice of learning physics, Advice of revising and preparing for exams, Topic summaries.

49. Revision Advice for Students Prepare 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.

50. Revision Advice for Students In the two weeks before the exam: Use the draft with past exam and trail papers, Evaluate performance after each exam and revise draft of four page summary accordingly.

51. Exam Advice for Students Use the 15 minute reading productively, Attitude: Remember if you are finding the exam fairly hard, don’t 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.

52. Exam Advice for Students Highlight data and important information as you read the question. Show working every time. Written response: Answer in point form. Don’t look for complexities in the question. Assume the simplest explanation.

53. Resources Past Exam Papers and Solutions Chief Assessor Reports Exam Statistics Practice Papers

54. Resources Past Exam Papers and Solutions Papers VCAA: 2002 – 2013VCAA Checkpoints (Cambridge) $29 per unit Solutions Vicphysics: 1999 – 2013 (for students with marking scheme)Vicphysics

55. Resources Chief Assessor Reports VCAA General comments including:VCAA *Areas of concern, *Advice. For each question: *The percentage getting each score from 0 to max, *Specific comment, e.g. common errors

56. Resources Exam Statistics VCAA Score ranges for each letter grade and grade distributions for the exam and the internal assessment for males and females for 2013.VCAA Vicphysics Raw score cut offs for 1999 – 2013.Vicphysics

57. Resources Practice Papers STAV IARTV NEAP TSSM A+ Publishing TSFX itute