PHYSICS EXAMINATIONS – 2006 Bruce Walsh

REMINDERS  Calculators  Study design and textbooks  Examiners report  VASS system  SSMS

JUNE EXAMINATION

STATISTICS  6712 students  Mean = 90 = 50%  Std dev = 38.7 = 21.5%  Number achieving 100% = 0

GRADE MIN (/180) MIN (%) A A12670 B B9251 C+7642 C6234 D+4827 D3821 E+3017 E2413

 Reasonably challenging paper  Detailed studies  Attempt ONE detailed study only  Explanations address specific question. – Diagrams  Show working GENERAL COMMENTS

 Converting units  Calculations – powers of 10 - raising to power eg. R 3 - raising to power eg. R 3  Care reading scale on axes  Multiple choice questions  Illegible writing

PROBLEM AREAS MOTION  Q3. Two stage – get acc from F=ma then use const acc formula. Many assumed a=9.8. Few used W=ΔE K  Q6. Net force. Many neglected gravity. Others added it instead of subtracting  Q7. Multiple steps. Net force const. Use F=ma for acc then const acc for dist. OR I=Δp for speed then const acc for dist. Many assumed acc was g

 Q8. Two components then Pythagoras. Multiple steps  Q11. I=Δp or get acc then f=ma Easier to treat space station than shuttle (3 rd law). Confusion over masses and speeds  Q12. Conservation of energy. Some fudging

 Q14. Conservation of energy. Loss of Grav PE = Gain in Spring PE. Many used F=-kx assuming f=mg at bottom

ELECTRONICS & PHOTONICS  Q1. DC biasing. Parts 2 and 3 poorly done  Q3. Signal voltage - clipping  Q4. Decoupling capacitor. Most knew what it did but not why  Q8. Modulation

RELATIVITY  Q7-9. Confusion over frames of reference.

MATERIALS & STRUCTURES  Q3. Reading axis ε =2% not 2  Q4. Calculated wrong material or misread strain axis  Q6. Work = Area of graph x Volume Many forgot volume or had calculation difficulties

FURTHER ELECTRONICS  Q7. Operation of regulator

NOVEMBER EXAMINATION

STATISTICS  6589 students  Mean = 111 = 62%  Std dev = 41 = 23%  Number achieving 100% = 20

GRADE MIN (/180) MIN (%) A A15083 B B11564 C+9854 C8246 D+6637 D5028 E+3620 E3017

GENERAL COMMENTS  Accessible paper  Detailed studies  Illegible writing  Explanations must address specific question

 Explanations – one mark per point  Show working  Unit conversions, eg. cm 2 to m 2  Read questions carefully. Answer what is asked not what you expect to be asked.

PROBLEM AREAS ELECTRIC POWER Q1. Sketching magnetic fields. Q1. Sketching magnetic fields. Q8. E.M. induction. Trouble calculating area (units) and getting correct time Q8. E.M. induction. Trouble calculating area (units) and getting correct time Q Operation of transformer Q Operation of transformer Q16. Overall distribution system Q16. Overall distribution system

LIGHT and MATTER  Q1. Incoherent light from wide spectrum sources. Confused with discrete emission spectrum.  Q2. Wave and particle predictions for PE effect.  Q6. Meaning of standing waves for electrons in stable states in atoms.

 Q11. Distinction between matter and electromagnetic radiation. Wrong Planck’s constant. Assumption that because momentum was the same, energy was also. Electron speed taken as 3x10 8.

SYNCHROTRON  Q2. Explain two advantages.  Q5. Relate greater wavelength to reduced energy.

PHOTONICS  Q5. Operation of graded index multimodal fibres  Q6-7. Snell’s law  Q10. Rayleigh scattering increases as wavelength decreases.

SOUND  Q6. Sound from front and rear out of phase, box prevents interference.  Q9. Unable to explain resonance in terms of behaviour of sound waves.