6 Common Mistakes HSC Physics Students Make in Exams
Posted on September 6, 2017 by DJ Kim
Read the 6 Common Mistakes HSC Physics Students Make in Exams. Learn the errors HSC students are making and avoid them.
Mistake #1: Incorrect interpretation of Key Verbs
Do you know how to respond to the key verbs correctly?
For example, in answering ‘Explain’ questions, most students are giving a description not an explanation. Learn How to answer ‘Explain’ questions present in the HSC Physics Exam.
Assess the impact on society and the environment of the potential applications of superconductors.
Sample Response 1
|Application of superconductor||Impact on Society||Impact on Environment||Assessment|
|Superconducting Generation of Power||
Mistake #2: Insufficient Workings for Calculations
Did you know that 2 marks are allocated in a simple calculation question?
- 1 mark for correct formula and substitution and
- 1 mark for the correct answer
In questions requiring numerical answers, you should always
- show the working in a clear and logical fashion
- round-off answers at the end of the calculation instead of during the parts of the calculation.
In the example below, the student made the correct substitution but did not square the denominator and as a result got an incorrect answer. However the student was still awarded one mark
If you have made a calculation mistake, you may still be awarded marks for your working, so it must always be clearly shown.
Mistake #3: Write units. I mean correct SI Units!
Students forget to provide the correct units with their numerical answers.
What is wrong with this student’s answer regarding the magnitude of acceleration?
“The acceleration of the rocket is 15 m/s.”
Make sure you know the SI units for the following:
- potential difference
In the example below, the student lost a mark for not stating the SI Unit.
Mistake #4: Line of Best Fit?
When drawing a line of best fit, students must identify and eliminate any outliers before determining the trend. In the diagram shown below, if a student does not recognise the outlier then he/she will draw an incorrect line of best fit (dotted line). However once you remove the outlier from trend, then you can draw a correct line of best fit (solid line).
Mistake #5: Confusion about Validitiy, Reliability and Accuracy?
When students are asked how you would improve the accuracy of your experimental results, they often reply with a statement such as “repeat the experiment many times”. Does this sound like you? If so, then expect to lose at 3 – 4 marks in your HSC Exam this year.
Here is an outline of the differences between validity, reliability and accuracy:
|Definition||Technique used in pendulum experiment|
|Validity||Validity is how appropriate the pro
cedure and materials are to achieve a desired experimental result.
|Swinging the pendulum through small amplitudes to ensure the equation given could be applied.|
|Reliability||Reliability is how repeatable the experment is. Do you get very similar results every time?||Starting and stopping the stopwatch at the extremes of the motion ensures more repeatability than trying to start and stop mid-swing.|
|Accuracy||Accuracy is how close the value calculated from the experiment is to the accepted true value.||Use of more precise measuring devices such as a data logger and a sensor would improve accuracy.|
Mistake #6: Human error is not a valid type of experimental error!
When students are asked about how to improve the reliability and accuracy of the experimental results, most state “reduce human error!” Human error is not a valid type of experimental error! The two types of experimental error explored in physics experiments are random and systematic errors.
Random errors are caused by unknown and unpredictable changes in the experiment, e.g. due to the instruments or environmental conditions. These arestatistical fluctuations in both directions about the true value thus repetition and statistical analysis can reduce the effects. To help reduce random errors:
- Make sure you know how to read the scales on the instruments and that you align yourself properly each time you take a measurement.
- Take multiple measurements (repetition increases reliability!) and then take an average for the result
Systematic errors are caused by measuring instruments being used incorrectly or problems with the instrument itself. Systematic errors limit accuracy. To help reduce systematic errors:
- All instruments should be checked against a standard before use. Zero settings should be checked and adjusted (calibration!).
- Instructions for the use of the instrument should be read and followed.
- Corrections for instrument bias should be made (if necessary).
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- Revise the core topics in detail;
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