Physics end of year exam advice 2014
Start preparing your notes now, by Craig Tilley
The Physics examination tests units 3 & 4. Topics are Motion in one and two dimensions and
Electronics and photonics (covered in the Herald Sun article 6th
May 2014), Electric Power and
Interactions of light and matter, then one of six Detailed Studies. Total is 150 marks in 150 minutes
so pace yourself and try to leave some time to check your answers.
You are allowed one folded A3 sheet or two taped A4 sheets of notes and one scientific calculator
in the exam. Start preparing your notes now. Use the VCAA formula sheet, or download one - it is
at the back of last years exam PDF. Have this handy when you start drafting your notes. VCAA
number the formulas, but they are grouped by topic and there is some overlap between topics.
Generally: formulas 1-11 go with Motion in one and two dimensions, 12-14 go with Electronics and
Photonics, 15-19 go with Electric Power, 20-28 go with Interactions of light and matter. Then the
Detailed Studies follow with 29-33 going with Synchrotron and its applications, 34 & 35 go with
Photonics, 36 is for Sound, 37-41 go with Einsteins special relativity, 42-44 go with Materials and
their use in structures and formula 45 goes with Further Electronics. Formulas 46 to 51 may be used
by different topics.
The formula sheet only lists some of the formulas for each topic. To draft your notes, work through
some past VCAA papers or the commercial ones bought by your school, or the A+ Exam practice
book. Attempt a question and identify the topic: Motion in one and two dimensions, Electronics and
photonics etc. Try to get the answer using your existing knowledge, dont look anything up yet. If
you can, thats good news. Correct your answer from the solutions. If you cant do the question, this
tells you something and its good news too. Learn from it. Consult the solution and work out what it
tells you. Add any formulas to your draft notes under the topic heading. Any concepts you didnt
recall? Add them to your notes too. Continue with the next question. Dont try to do a whole exam
in a set amount of time just yet, thats for closer to exam time. Doing questions and adding to your
notes is one of the best ways to study Physics (and other subjects too)! So, keep going. Get more
past and trial papers. Revise your notes from time to time and delete anything you remember well to
make more space. It is a work in progress and might not be finished until right before the exam.
Now to complete my Unit 4 advice for this year.
To determine the magnetic field direction at a point, determine the field from each magnet
separately and add as vectors.
Voltage from a generator is given by Faradays law and current direction is given by Lenzs law.
The direction of induced current has three steps:
1. What flux change is occurring?
2. What would oppose this (or restore the original)?
3. Hence what is the current direction?
DC motors and generators utilise a split ring commutator while AC utilise slip rings.
A shape of a voltage-time graph follows the negative gradient of the flux-time graph.
Transmission lines form series circuits with long wires that lose voltage and power. The voltage of
the power supply (e.g. 200 V) is lost along the sum of both lines and the output (e.g. 12 V along
each transmission line and 176 V at the load). Power values follow the same pattern. Current is the
same in each.
Interactions of light and matter
Use h = 4.14 1015
for electron volt energy (eV). Otherwise use h = 6.63 1034
momentum h = 6.63 1034
Js & energy must be in joules (J).
Energy level diagrams: longest wavelength will have lowest energy and lowest frequency. Shortest
wavelength will have highest energy and highest frequency.
Photoelectric effect involves energy. Incident light has energy (hf), and if above the minimum for
the electrons (W), any excess energy becomes the electrons kinetic energy (KEmax).
So: hf = W + KEmax
And: hf = hfo + qVo where fo = threshold frequency & Vo = stopping voltage.
If light intensity increases, everything stays the same, simply more current flows.
If light frequency increases, light energy & KEmax increase, W remains the same.
If the metal changes, f stays the same, W changes & so KEmax changes.
If f < fo ; Elight < W so no photoelectrons are ejected.
In Youngs experiment the central max is bright as PD = 0. Other maximums are bright as PD = n.
Minima are dark as PD = (n ) . The n number is the line number from the central maximum
where n = 0. The band spacing (x) is determined from: x ( L) / d and x L / (f d).
Electron diffraction compares to X-ray diffraction if the electrons de Broglie wavelength compares
to the X-ray wavelength. Electrons have NO frequency & do NOT travel at c. Wavelength and
momentum are linked for electrons but NOT wavelength and energy.
Craig Tilley has been a Physics examination assessor for over 15 years and is the author of the
A+ Physics Units 3 & 4 Exam Book and co-author of A+ Physics Notes.