Tag: HSC physics

4 ways to avoid common errors in HSC Physics

Getting those few extra marks can be tough. Not only does the HSC Physics exam test our knowledge of the subject but also our ability to convey that to the marker for any given question. Getting everything down onto the paper itself is a milestone, and that’s before you count the challenging questions that can leave you stumped! Then you get your paper back, aside from what you expected… There are all the careless mistakes and marks taken for seemingly frivolous things like the heading to a graph. HSC Physics sure is tough, but here are four ways to avoid those unexpected surprises that we can all do without!

1. Always check the units

Everyone knows about checking the units in your final answer, but have you ever considered the units the question comes with? It seems obvious, speed is in m/s and frequency is in Hertz. But the place where many students trip up is in the Space module, most of the measurements in the question are given in kilometres however all the equations in the data sheet are based on SI units so are in metres. Remember to times by 1000 in these cases and watch out for other prefixes like micro- and nano- when doing wavelength calculations. Always think about your answer, if the altitude your orbiting satellite is 100 metres you should probably try again!

2. Underline the key words of the question

You’ve probably heard this piece of advice time and time again. However, hardly any students end up following the advice. I remember wishing I had taken the effort to underline the keywords in the question when I lost that easy mark for not giving a final evaluation in a 7 marker. Teachers and physics tutors would have told you that the main reason for underlining the words in the question is to make sure you’ve covered everything. While this is true, we all know it’s all too easy to underline and forget! Make sure you tick of each piece of underlined information so that you truly haven’t missed anything and get the most out of your efforts!

3. Use a diagram or table

Tackling those large mark questions is tough! The very thought of having to write down all that information used to dishearten me! I’ve found that the easiest way to reduce both the time and effort taken for these questions is to use a table or a diagram. At school or at physics tutoring, they normally recommend you do this for questions that have the key words "compare and contrast" but you can use this method in many more cases. A table can be used for "discuss" questions and "evaluate" questions while a diagram can help with explaining the galvanometer, induction cooktop or even the nuclear reactor to name a few. Not only are these diagrams and tables more readable, they also help you remember all the things you want to write about as you remember it in a visual fashion. Dot-points can also be used when answering questions normally in order to save on writing which can really help out on the 3 hour papers. Remember your diagrams and tables and fight back against the wall of text!

4. Leave time to check

This rule is almost universal to every exam and in a perfect world we all wish we could do it. Leaving time to check is an approach that shapes how you tackle the whole exam. If you want to save time in the exam, it’s best to practice earlier, the most straightforward way is doing all the practice papers in about 75% of the actual time in order to develop speed. Additionally, with more practice questions will become easier to answer and you will spend less time trying to remember the points. While we can save some time for checking, it isn’t infinite and needs to be prioritised. The first thing to check is always the mistakes you make most commonly so as to pick up the easiest errors first, then checking the calculations by doing them again separately and lastly by adding anything at all that could be relevant to the answer that you can think of! Remember, as long is its right, it can’t hurt. This method for checking means that even if you run out of correction time you’ve been as efficient as possible with your time meaning better exam performance.

A student’s worst enemy is the marks they could have gotten but missed out on. The above methods stem the tide against losing ‘easy marks’. Hopefully they help you get those last few marks you’ve been yearning for in HSC Physics!

HSC Physics Experiments

Experiment one: The Motor Effect

For the HSC Physics syllabus dot-points:

  • Perform a first-hand investigation to demonstrate the motor effect
  • Perform an investigation to model the generation of an electric current by moving a magnet in a coil or a coil near a magnet
  • Plan, choose equipment or resources for, and perform a first-hand investigation to predict and verify the effect on a generated electric current when: the distance between the coil and magnet is varied, the strength of the magnet is varied, the relative motion between the coil and the magnet is varied
  • Plan, choose equipment or resources for, and perform a first-hand investigation to demonstrate the production of an alternating current

For the first dot-point, we wound wires five times, threading each loop through the region between two strong permanent (neodymium) magnets. We then applied a current of 3 amps through the wire (our power supply was auto current-limiting so no excessive heat was produced). With 5 loops threaded, each with 3 amps, the total effective current was 3×5 = 15amps, and a movement of the wires were observed. The direction of force on the wire was as predicted by the right-hand push rule (aka right-hand palm rule).

For the second dot-point, we tested each condition (distance, strength and speed of magnet) on a coil connected to an ammeter and we observed a direct correlation between strength of magnet and induced current, a direct correlation between speed of magnet and induced current, and an inverse correlation between distance of magnet and induced current.

For the final dot-point, we moved a magnet in and out of a coil connected to an ammeter. The ammeter needle’s direction of movement continually reversed, indicating that an alternating current was produced. We also used a hand-wound AC generator to power an incandescent light bulb.

Experiment two: Transformers and Induction motors

For the HSC Physics ( http://www.duxcollege.com.au/ ) syllabus dot-points:

  • Perform an investigation to model the structure of a transformer to demonstrate how a secondary voltage is produced
  • Perform an investigation to demonstrate the principle of an AC induction motor

For the first dot-point, we constructed a model transformer using a 300 turn coil as the primary and a 600 turn coil as the secondary. Primary voltage was 18V AC and the secondary voltage was measured (by an AC-capable voltmeter) to be approx 35V AC when using laminated iron cores. The secondary voltage was observed to fall significantly (around 22V) when laminated iron core was replaced with a solid bar of iron (more eddy currents were possible with unlaminated iron core, decreasing efficiency of the magnetic flux transfer). We then switched the primary and secondary coil so that the primary was now 600 turns and the secondary was 300 turns. The secondary voltage was measured to be 8.5V AC. The percentage inefficiency was calculated to be the same in the step up and step down versions.

For the secondary dot-point, we constructed a single phase squirrel cage induction motor. Single phase induction motors generate initial torque due to the presence of shading coils. These coils delay the flux transfer at carefully chosen parts of the surrounding stator so that the initial change in flux produces a torque on the rotor. The squirrel cage core is not connected to any electricity — it moves only due to Lenz Law — it chases the external rotating magnetic field. We observed that the speed of the induction motor was at its highest if using a laminated core. When we changed the orientation of the rotor so that flux has to pass through a section of air, we observed the motor slow down significantly. When we bridged this gap with a solid iron bar, the rotor sped up slightly, but was still slower than its original speed. This again illustrates that air and iron bars are not as effective in transferring magnetic flux as laminated iron.

HSC Biology first-hand investigations coming soon!

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