Physics is a really easy subject to make a mistake in. I’ve made a whole bucket load of mistakes in Physics over the years. In fact, I continue to make mistakes in Physics at the tertiary level. Put simply, it’s a bloody hard area of study with many opportunities to make mistakes. The key to avoiding these mistakes is being aware of where they can happen, because once you know where they are, they become much easier to spot and even easier to avoid.
This is the next in the “Avoidable Mistakes” series. Be sure not to make these mistakes in your Physics exams.
1. Not Converting to SI Units
I start with this because no matter how many times I told myself to do it, no matter how many times I forgot… I almost always did it again, only spotting my mistake in the few minutes at the end of an exam. For every mathematical question, be sure to convert all your units to SI units before you use them. Make it part of your process!
PS – If you don’t have a process for Mathematical Physics Questions, Jake can help you out with the awesome guide he wrote here).
2. Right Hand Rule Errors
The right hand rule is used for a number of reasons in the Motors and Generators topic, primarily for determining the direction of electromagnetic forces. However, there is a trap hidden in many of these sorts of questions. Take this extract from a part of HSC 2015 Physics Paper:
Calculate the force on an electron due to the electric field between the cathode and the anode.
Without seeing the context, this question requires a magnitude (obtained via formula) and a direction. You get this direction by the right hand rule, but can you spot the trap?
The Right Hand Error gives the direction on a positively charged particle.
The question specifies an electron, which is negatively charged. Many students will not account for this and give the wrong direction.
So, make sure that if you are using the right hand rule to find the direction on a negatively charged particle, you reverse the direction you get at the end.
3. Direction and Units
Speaking of units and directions… Make sure to include both when required! Not including units in any question with a quantitative answer will automatically cost a mark, and the same is true for not including a direction with a vector quantity. This includes but is not limited to: forces, acceleration, current, magnetic fields, etc.
4. Not Using the Formula Sheet
I asked a friend of mine who did well in HSC Physics what his number one tip was. I was expecting something insightful and provocative. I got this:
“The formula sheet is really useful since it has the formulas on it.”
This may seem really stupid, but you’d be surprised how many students forget that they have the Formula Sheet at the back of the exam. They rip it off, get busy working, and then forget all about it under pressure. Obviously, you would be better off knowing the formulas off by heart anyway, it saves you time and will generally mean you know the content more effectively. However, the formula sheet can save you: Don’t forget it is there.
5. Incorrect Responses to Practical Questions
There is guaranteed to be at least one question in your HSC Exam regarding one of the many practical experiments you performed throughout the course. These questions cause issues for many students because they, quite simply, don’t think they need to know that content. But you do.
Questions in this area often revolve around concepts you may not have covered explicitly since Preliminary Physics. Be sure you know the difference between reliability (similar results as an experiment is repeated), accuracy (obtaining results close to the expected result), and validity (variables controlled and precision of measuring equipment). Further, be ready to suggest improvements to the experiments you did in class, and/or suggest sources of error.
As you can probably tell, this is quite a large chunk of content. It could be worth 4-6 marks in your exam; that is the difference between a Band 5 or Band 6. Don’t get caught out!
6. Vector Addition
Questions in various areas of the course (Motors and Generators and Projectile Motion are two examples) may require vector addition. This is covered in the preliminary course, but is a little neglected in Year 12.
Ensure that, when adding vector quantities, you are aware of and compensate for their directions. An object being pushed upwards by 9.8N and downwards by 9.8N will behave completely differently to an object being pushed sideways by 19.6N.
Compensating for vector direction may involve trigonometry (depending on the angles involved). Much more commonly, it will usually simply involve addition/subtraction along a single axis. The math is easy; as long as you remember to do it in the first place.
7. Forgetting Physics Terminology
Terminology is absolutely everything in science. So, as a more general downfall to avoid at all costs, make sure to use the proper jargon. This is especially true in the longer, 6 mark conceptual responses.
Consider the two mini-responses below to this question: How does doping affect the way a current is carried in a semiconductor? One uses jargon much more effectively than the other.
Doping involves adding extra things to a semiconductor to change the number of free positive and negative charges. The negative charges are electrons and the positive charges are where there are gaps for electrons. There are two types of doping, one type gives more electrons, one gives more gaps.
Doping involves the addition of Group 3 or Group 5 elements to create an extrinsic semiconductor, with the differences in atomic structure altering how current is carried. Group 5 doping elements introduce additional electrons to act as charge carriers, whereas Group 3 elements introduce additional electron vacancies, or “holes,” to act as charge carriers.
It is clear which of these is more effective. Using the proper terminology allows more information to be expressed more succinctly, and enables you to properly understand any question that is thrown at you. This is super important in every part of the exam. If you are looking for some great Physics notes, look no further than our Free Notes Section!
8. Working Alone
I am of the opinion that HSC Physics is one of the most difficult subjects you can do, at least in terms of the complexity of the concepts you are required to understand. You are, as a 17/18-year-old student, expected to understand and explain some of the most groundbreaking discoveries in classical and quantum physics. This is an insanely difficult task, but it is made much easier by working with others.
A massive amount of my Physics study involved working in study groups, where the confident learners take a ‘teacher’ role and help the others. This helps the confident people consolidate their knowledge, and the less confident people get better explanations from students who are doing the course. We had extra discussions with our teacher, I used to get my family to test me on terminology: I was always working with others, and you should be to. HSC Physics should not be done alone!
Obviously, the ultimate manifestation of this is getting involved on ATAR Notes. Get your questions answered, and get advice from Band 6 students such as Jake and myself. Take advantage of our free HSC Tutoring. Work together to achieve success!
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