As students prepare for their exams, questions that only assessors can answer often pop into mind. Unfortunately, most students don’t have access to assessors in most of their subjects, so we took your questions and presented them to a senior VCAA assessor who has extensive experience in marking the VCE exams that you will soon sit. Here are his/her answers.
We hope that your exam preparations are going well.
What is the go in regards to rounding to significant figures in an exam? Do answers have to be to correct significant figures? Do you get penalised for significant figures?
There is no penalty for significant figures, but there are guidelines to make answers look better.
E.g. Find the acceleration when a force of 23.0 N acts on a mass of 8.1 Kg.
Apply F = ma
a=F/m = 23.0/8.1 = 2.8 ms-2
This is the correct answer, as the least accurate information had 2 significant figures. The answer 2.84 is also OK as it only adds one figure. If you include 2.839506173 it is very unlikely that marks are deducted, but this wastes time writing all the figures and makes the student look incompetent. If you shorten the correct answer of 2.8 to 3 you will almost certainly lose marks.
Can a line of best fit be extrapolated past data points?
Yes, within reason. If it is a Photoelectric graph the question may require extrapolating to intersect the EKmax (vertical) axis. This enables the work function to be estimated/read from the intercept.
If we get an answer correct but the working out is wrong for a calculation question, will we still get full marks if it’s a 2 or 3 mark question??
The instructions have changed over the last 5 years. You no longer get full marks for the correct numerical answer.
This is from the instructions in Section B last year:
‘In questions where more than one mark is available, appropriate working must be shown.’
The ‘must’ means that without correct working to match the answer then full marks cannot be awarded. In many questions it actually means zero marks, even with the correct answer.
While doing projectile motion questions do I have to use ‘uvats’ or can I use Specialist Maths techniques such as r(t)?
It is perfectly fine to use techniques learned in Specialist Maths. The same guidelines apply, no matter which way you approach the question. Ensure that the working is clear and add some explanatory words to clarify what you are doing.
How do I go about answering questions that relate to Heisenberg’s uncertainty principle or the single slit diffraction experiment that supports his theory?
The questions so far on this topic, from the exams, have been very confusing. There seems to be some misunderstanding about the coordinates of uncertainty. The first video below goes a little beyond the course, but is very clear about directions and how it works.
The second video is simpler, and gives a nice practical demonstration of single slit diffraction.
The important thing to remember is that: only becomes relevant for very small masses. The uncertainty in position and the uncertainty in momentum are in the same direction. This is very clear from the videos.
How do you allocate your working out for 3 marks? Do you need to include how you derived the formula, and then substitution of numbers?
There is no need to include derivation of formulas. There may be marks allocated for the derivation, but provided that your derived formula is correct the marks are still awarded.
GMm/R2 = m4?2R/T2
Which then gives
T = (4?2R3/GM)^2
The ability to derive the required versions is expected. Having the whole set accurately on your sheet saves a lot of time. You still get the marks for getting the correct version from your sheet.
Always include the step with the correct numbers in the correct places, followed by the answer.
When writing a formula sheet for the exam, what would be your recommendation to what should be included and what not should be included?
There are 2 parts to this answer. Each student will have different needs for the sheet. These are some ideas. (This is not meant to be the ideal list.)
Work through at least one recent exam and then include everything you needed to check. You should end up with room for examples. The examples should come from the patterns starting to emerge from the 4 exams on the current course. e.g. Have some theory answers ready for the Photoelectric Effect. The danger is in not being adaptable to the specific question. It is obvious when a prepared answer is copied but does not quite match the question. You need to be able to explain the ways that each model supports and also fails for the Photoelectric Effect. Perfect rehearsed answers will help refine your understanding of the more difficult theory. Have some answers ready about Atomic Energy levels and their relationship with standing De Broglie wavelengths.
Include everything that is difficult to remember or derive under the stress of exams.
Area 1 Fields:
- Include all versions of the formulas that have been rearranged. Include graphs of field Vs distance and force vs distance.
- Make sure you know how to get the energy from each graph.
- Motors – be able to explain how and why a motor works.
Area 2: Use of fields
- Generators – be able to explain that all generators are AC and that the only change to get DC is the connections.
- Have the reasoning steps for Lenz’s Law with only talking about flux change not fields.
- Transformers – When describing reduction of power losses always mention constant power.
- Have an example of a distribution system so you can work forwards or backwards.
Area 3: Motion
- Have examples of pulleys, towing etc. They are all based on ?F = ma
- Examples of circular motion, both horizontal and vertical. Banked tracks example.
- Projectiles examples. Conservation of momentum and inelastic collision examples.
- Relativity – make sure you understand the perspective and include it in the answer. Question 11c from 2017. If you did not include your perspective there were zero marks.
- Have a worked example of vertical spring energies.
Area 4: Waves
- Slow and fast spring interactions – have a diagram.
- Standing wave diagrams.
- Refraction examples plus dispersion.
- Interference diagrams from multiple perspectives. Be able to calculate and explain path differences.
- Electromagnetic spectrum.
Area 5: Wave-particle duality
Must be able to understand this area of study – these can be the high end questions.
- Electron Volt conversions.
- Photoelectric effect – must be able to explain. Include diagrams and calculations.
- Examples of questions that talk about particle diffraction or interference.
- Absorption and emission spectra.
- Atomic energy levels and their connection to De Broglie wavelengths of electrons.
- Heisenberg’s uncertainty – probably only have to explain the effect of reducing gap size for a particle stream.
Scales must be even and suitable for the sheet provided. Practice uncertainty bars.
Extended practical investigation:
Variables, accuracy, precision, systematic and random errors.